765 lines
30 KiB
Plaintext
765 lines
30 KiB
Plaintext
<!--
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$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.33.4.2 2010/05/13 18:29:45 tgl Exp $
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-->
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<chapter id="pltcl">
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<title>PL/Tcl - Tcl Procedural Language</title>
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<indexterm zone="pltcl">
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<primary>PL/Tcl</primary>
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</indexterm>
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<indexterm zone="pltcl">
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<primary>Tcl</primary>
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</indexterm>
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<para>
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PL/Tcl is a loadable procedural language for the
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<productname>PostgreSQL</productname> database system
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that enables the <ulink url="http://www.tcl.tk/">Tcl</ulink>
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language to be used to write functions and
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trigger procedures.
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</para>
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<!-- **** PL/Tcl overview **** -->
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<sect1 id="pltcl-overview">
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<title>Overview</title>
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<para>
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PL/Tcl offers most of the capabilities a function
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writer has in the C language, except for some restrictions.
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</para>
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<para>
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The good restriction is that everything is executed in a safe
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Tcl interpreter. In addition to the limited command set of safe Tcl, only
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a few commands are available to access the database via SPI and to raise
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messages via <function>elog()</>. There is no way to access internals of the
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database server or to gain OS-level access under the permissions of the
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<productname>PostgreSQL</productname> server process, as a C function can do.
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Thus, any unprivileged database user may be
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permitted to use this language.
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</para>
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<para>
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The other, implementation restriction is that Tcl functions cannot
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be used to create input/output functions for new data types.
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</para>
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<para>
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Sometimes it is desirable to write Tcl functions that are not restricted
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to safe Tcl. For example, one might want a Tcl function that sends
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email. To handle these cases, there is a variant of <application>PL/Tcl</> called <literal>PL/TclU</>
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(for untrusted Tcl). This is the exact same language except that a full
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Tcl interpreter is used. <emphasis>If <application>PL/TclU</> is used, it must be
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installed as an untrusted procedural language</emphasis> so that only
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database superusers can create functions in it. The writer of a <application>PL/TclU</>
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function must take care that the function cannot be used to do anything
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unwanted, since it will be able to do anything that could be done by
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a user logged in as the database administrator.
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</para>
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<para>
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The shared object for the <application>PL/Tcl</> and <application>PL/TclU</> call handlers is
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automatically built and installed in the
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<productname>PostgreSQL</productname>
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library directory if Tcl support is specified
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in the configuration step of the installation procedure. To install
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<application>PL/Tcl</> and/or <application>PL/TclU</> in a particular database, use the
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<command>createlang</command> program, for example
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<literal>createlang pltcl <replaceable>dbname</></literal> or
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<literal>createlang pltclu <replaceable>dbname</></literal>.
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</para>
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</sect1>
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<!-- **** PL/Tcl description **** -->
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<sect1 id="pltcl-functions">
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<title>PL/Tcl Functions and Arguments</title>
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<para>
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To create a function in the <application>PL/Tcl</> language, use the standard syntax:
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<programlisting>
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CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
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# PL/Tcl function body
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$$ LANGUAGE pltcl;
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</programlisting>
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<application>PL/TclU</> is the same, except that the language has to be specified as
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<literal>pltclu</>.
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</para>
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<para>
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The body of the function is simply a piece of Tcl script.
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When the function is called, the argument values are passed as
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variables <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal> to the
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Tcl script. The result is returned
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from the Tcl code in the usual way, with a <literal>return</literal>
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statement.
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</para>
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<para>
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For example, a function
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returning the greater of two integer values could be defined as:
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<programlisting>
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CREATE FUNCTION tcl_max(integer, integer) RETURNS integer AS $$
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if {$1 > $2} {return $1}
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return $2
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$$ LANGUAGE pltcl STRICT;
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</programlisting>
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Note the clause <literal>STRICT</>, which saves us from
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having to think about null input values: if a null value is passed, the
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function will not be called at all, but will just return a null
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result automatically.
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</para>
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<para>
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In a nonstrict function,
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if the actual value of an argument is null, the corresponding
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<literal>$<replaceable>n</replaceable></literal> variable will be set to an empty string.
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To detect whether a particular argument is null, use the function
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<literal>argisnull</>. For example, suppose that we wanted <function>tcl_max</function>
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with one null and one nonnull argument to return the nonnull
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argument, rather than null:
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<programlisting>
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CREATE FUNCTION tcl_max(integer, integer) RETURNS integer AS $$
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if {[argisnull 1]} {
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if {[argisnull 2]} { return_null }
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return $2
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}
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if {[argisnull 2]} { return $1 }
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if {$1 > $2} {return $1}
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return $2
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$$ LANGUAGE pltcl;
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</programlisting>
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</para>
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<para>
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As shown above,
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to return a null value from a PL/Tcl function, execute
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<literal>return_null</literal>. This can be done whether the
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function is strict or not.
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</para>
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<para>
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Composite-type arguments are passed to the function as Tcl
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arrays. The element names of the array are the attribute names
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of the composite type. If an attribute in the passed row has the
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null value, it will not appear in the array. Here is an example:
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<programlisting>
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CREATE TABLE employee (
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name text,
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salary integer,
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age integer
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);
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CREATE FUNCTION overpaid(employee) RETURNS boolean AS $$
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if {200000.0 < $1(salary)} {
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return "t"
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}
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if {$1(age) < 30 && 100000.0 < $1(salary)} {
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return "t"
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}
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return "f"
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$$ LANGUAGE pltcl;
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</programlisting>
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</para>
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<para>
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There is currently no support for returning a composite-type
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result value, nor for returning sets.
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</para>
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<para>
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<application>PL/Tcl</> does not currently have full support for
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domain types: it treats a domain the same as the underlying scalar
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type. This means that constraints associated with the domain will
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not be enforced. This is not an issue for function arguments, but
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it is a hazard if you declare a <application>PL/Tcl</> function
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as returning a domain type.
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</para>
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</sect1>
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<sect1 id="pltcl-data">
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<title>Data Values in PL/Tcl</title>
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<para>
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The argument values supplied to a PL/Tcl function's code are simply
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the input arguments converted to text form (just as if they had been
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displayed by a <command>SELECT</> statement). Conversely, the
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<literal>return</>
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command will accept any string that is acceptable input format for
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the function's declared return type. So, within the PL/Tcl function,
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all values are just text strings.
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</para>
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</sect1>
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<sect1 id="pltcl-global">
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<title>Global Data in PL/Tcl</title>
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<indexterm zone="pltcl-global">
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<primary>global data</primary>
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<secondary>in PL/Tcl</secondary>
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</indexterm>
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<para>
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Sometimes it
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is useful to have some global data that is held between two
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calls to a function or is shared between different functions.
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This is easily done in PL/Tcl, but there are some restrictions that
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must be understood.
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</para>
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<para>
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For security reasons, PL/Tcl executes functions called by any one SQL
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role in a separate Tcl interpreter for that role. This prevents
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accidental or malicious interference by one user with the behavior of
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another user's PL/Tcl functions. Each such interpreter will have its own
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values for any <quote>global</> Tcl variables. Thus, two PL/Tcl
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functions will share the same global variables if and only if they are
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executed by the same SQL role. In an application wherein a single
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session executes code under multiple SQL roles (via <literal>SECURITY
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DEFINER</> functions, use of <command>SET ROLE</>, etc) you may need to
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take explicit steps to ensure that PL/Tcl functions can share data. To
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do that, make sure that functions that should communicate are owned by
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the same user, and mark them <literal>SECURITY DEFINER</>. You must of
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course take care that such functions can't be used to do anything
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unintended.
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</para>
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<para>
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All PL/TclU functions used in a session execute in the same Tcl
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interpreter, which of course is distinct from the interpreter(s)
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used for PL/Tcl functions. So global data is automatically shared
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between PL/TclU functions. This is not considered a security risk
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because all PL/TclU functions execute at the same trust level,
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namely that of a database superuser.
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</para>
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<para>
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To help protect PL/Tcl functions from unintentionally interfering
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with each other, a global
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array is made available to each function via the <function>upvar</>
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command. The global name of this variable is the function's internal
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name, and the local name is <literal>GD</>. It is recommended that
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<literal>GD</> be used
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for persistent private data of a function. Use regular Tcl global
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variables only for values that you specifically intend to be shared among
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multiple functions. (Note that the <literal>GD</> arrays are only
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global within a particular interpreter, so they do not bypass the
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security restrictions mentioned above.)
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</para>
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<para>
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An example of using <literal>GD</> appears in the
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<function>spi_execp</function> example below.
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</para>
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</sect1>
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<sect1 id="pltcl-dbaccess">
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<title>Database Access from PL/Tcl</title>
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<para>
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The following commands are available to access the database from
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the body of a PL/Tcl function:
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<variablelist>
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<varlistentry>
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<term><literal><function>spi_exec</function> <optional role="tcl">-count <replaceable>n</replaceable></optional> <optional role="tcl">-array <replaceable>name</replaceable></optional> <replaceable>command</replaceable> <optional role="tcl"><replaceable>loop-body</replaceable></optional></literal></term>
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<listitem>
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<para>
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Executes an SQL command given as a string. An error in the command
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causes an error to be raised. Otherwise, the return value of <function>spi_exec</function>
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is the number of rows processed (selected, inserted, updated, or
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deleted) by the command, or zero if the command is a utility
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statement. In addition, if the command is a <command>SELECT</> statement, the
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values of the selected columns are placed in Tcl variables as
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described below.
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</para>
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<para>
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The optional <literal>-count</> value tells
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<function>spi_exec</function> the maximum number of rows
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to process in the command. The effect of this is comparable to
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setting up a query as a cursor and then saying <literal>FETCH <replaceable>n</></>.
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</para>
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<para>
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If the command is a <command>SELECT</> statement, the values of the
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result columns are placed into Tcl variables named after the columns.
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If the <literal>-array</> option is given, the column values are
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instead stored into the named associative array, with the
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column names used as array indexes.
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</para>
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<para>
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If the command is a <command>SELECT</> statement and no <replaceable>loop-body</>
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script is given, then only the first row of results are stored into
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Tcl variables; remaining rows, if any, are ignored. No storing occurs
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if the
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query returns no rows. (This case can be detected by checking the
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result of <function>spi_exec</function>.) For example,
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<programlisting>
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spi_exec "SELECT count(*) AS cnt FROM pg_proc"
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</programlisting>
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will set the Tcl variable <literal>$cnt</> to the number of rows in
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the <structname>pg_proc</> system catalog.
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</para>
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<para>
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If the optional <replaceable>loop-body</> argument is given, it is
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a piece of Tcl script that is executed once for each row in the
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query result. (<replaceable>loop-body</> is ignored if the given
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command is not a <command>SELECT</>.) The values of the current row's columns
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are stored into Tcl variables before each iteration. For example,
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<programlisting>
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spi_exec -array C "SELECT * FROM pg_class" {
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elog DEBUG "have table $C(relname)"
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}
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</programlisting>
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will print a log message for every row of <literal>pg_class</>. This
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feature works similarly to other Tcl looping constructs; in
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particular <literal>continue</> and <literal>break</> work in the
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usual way inside the loop body.
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</para>
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<para>
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If a column of a query result is null, the target
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variable for it is <quote>unset</> rather than being set.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><function>spi_prepare</function> <replaceable>query</replaceable> <replaceable>typelist</replaceable></term>
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<listitem>
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<para>
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Prepares and saves a query plan for later execution. The
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saved plan will be retained for the life of the current
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session.<indexterm><primary>preparing a query</><secondary>in
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PL/Tcl</></>
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</para>
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<para>
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The query may use parameters, that is, placeholders for
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values to be supplied whenever the plan is actually executed.
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In the query string, refer to parameters
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by the symbols <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal>.
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If the query uses parameters, the names of the parameter types
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must be given as a Tcl list. (Write an empty list for
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<replaceable>typelist</replaceable> if no parameters are used.)
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Presently, the parameter types must be identified by the internal
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type names shown in the system table <literal>pg_type</>; for example <literal>int4</> not
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<literal>integer</>.
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</para>
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<para>
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The return value from <function>spi_prepare</function> is a query ID
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to be used in subsequent calls to <function>spi_execp</function>. See
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<function>spi_execp</function> for an example.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal><function>spi_execp</> <optional role="tcl">-count <replaceable>n</replaceable></optional> <optional role="tcl">-array <replaceable>name</replaceable></optional> <optional role="tcl">-nulls <replaceable>string</replaceable></optional> <replaceable>queryid</replaceable> <optional role="tcl"><replaceable>value-list</replaceable></optional> <optional role="tcl"><replaceable>loop-body</replaceable></optional></literal></term>
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<listitem>
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<para>
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Executes a query previously prepared with <function>spi_prepare</>.
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<replaceable>queryid</replaceable> is the ID returned by
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<function>spi_prepare</>. If the query references parameters,
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a <replaceable>value-list</replaceable> must be supplied. This
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is a Tcl list of actual values for the parameters. The list must be
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the same length as the parameter type list previously given to
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<function>spi_prepare</>. Omit <replaceable>value-list</replaceable>
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if the query has no parameters.
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</para>
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<para>
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The optional value for <literal>-nulls</> is a string of spaces and
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<literal>'n'</> characters telling <function>spi_execp</function>
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which of the parameters are null values. If given, it must have exactly the
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same length as the <replaceable>value-list</replaceable>. If it
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is not given, all the parameter values are nonnull.
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</para>
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<para>
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Except for the way in which the query and its parameters are specified,
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<function>spi_execp</> works just like <function>spi_exec</>.
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The <literal>-count</>, <literal>-array</>, and
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<replaceable>loop-body</replaceable> options are the same,
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and so is the result value.
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</para>
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<para>
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Here's an example of a PL/Tcl function using a prepared plan:
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<programlisting>
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CREATE FUNCTION t1_count(integer, integer) RETURNS integer AS $$
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if {![ info exists GD(plan) ]} {
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# prepare the saved plan on the first call
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set GD(plan) [ spi_prepare \
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"SELECT count(*) AS cnt FROM t1 WHERE num >= \$1 AND num <= \$2" \
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[ list int4 int4 ] ]
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}
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spi_execp -count 1 $GD(plan) [ list $1 $2 ]
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return $cnt
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$$ LANGUAGE pltcl;
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</programlisting>
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We need backslashes inside the query string given to
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<function>spi_prepare</> to ensure that the
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<literal>$<replaceable>n</replaceable></> markers will be passed
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through to <function>spi_prepare</> as-is, and not replaced by Tcl
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variable substitution.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<indexterm>
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<primary>spi_lastoid</primary>
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</indexterm>
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<term><function>spi_lastoid</></term>
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<listitem>
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<para>
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Returns the OID of the row inserted by the last
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<function>spi_exec</> or <function>spi_execp</>,
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if the command was a single-row <command>INSERT</>. (If not, you get zero.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><function>quote</> <replaceable>string</replaceable></term>
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<listitem>
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<para>
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Doubles all occurrences of single quote and backslash characters
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in the given string. This may be used to safely quote strings
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that are to be inserted into SQL commands given
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to <function>spi_exec</function> or
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<function>spi_prepare</function>.
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For example, think about an SQL command string like
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<programlisting>
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"SELECT '$val' AS ret"
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</programlisting>
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where the Tcl variable <literal>val</> actually contains
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<literal>doesn't</literal>. This would result
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in the final command string
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<programlisting>
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SELECT 'doesn't' AS ret
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</programlisting>
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which would cause a parse error during
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<function>spi_exec</function> or
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<function>spi_prepare</function>.
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To work properly, the submitted command should contain
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<programlisting>
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SELECT 'doesn''t' AS ret
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</programlisting>
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which can be formed in PL/Tcl using
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<programlisting>
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"SELECT '[ quote $val ]' AS ret"
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</programlisting>
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One advantage of <function>spi_execp</function> is that you don't
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have to quote parameter values like this, since the parameters are never
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parsed as part of an SQL command string.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<indexterm>
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<primary>elog</primary>
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<secondary>in PL/Tcl</secondary>
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</indexterm>
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<term><function>elog</> <replaceable>level</replaceable> <replaceable>msg</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Emits a log or error message. Possible levels are
|
|
<literal>DEBUG</>, <literal>LOG</>, <literal>INFO</>,
|
|
<literal>NOTICE</>, <literal>WARNING</>, <literal>ERROR</>, and
|
|
<literal>FATAL</>. <literal>ERROR</>
|
|
raises an error condition; if this is not trapped by the surrounding
|
|
Tcl code, the error propagates out to the calling query, causing
|
|
the current transaction or subtransaction to be aborted. This
|
|
is effectively the same as the Tcl <literal>error</> command.
|
|
<literal>FATAL</> aborts the transaction and causes the current
|
|
session to shut down. (There is probably no good reason to use
|
|
this error level in PL/Tcl functions, but it's provided for
|
|
completeness.) The other levels only generate messages of different
|
|
priority levels.
|
|
Whether messages of a particular priority are reported to the client,
|
|
written to the server log, or both is controlled by the
|
|
<xref linkend="guc-log-min-messages"> and
|
|
<xref linkend="guc-client-min-messages"> configuration
|
|
variables. See <xref linkend="runtime-config"> for more
|
|
information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</para>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="pltcl-trigger">
|
|
<title>Trigger Procedures in PL/Tcl</title>
|
|
|
|
<indexterm>
|
|
<primary>trigger</primary>
|
|
<secondary>in PL/Tcl</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Trigger procedures can be written in PL/Tcl.
|
|
<productname>PostgreSQL</productname> requires that a procedure that is to be called
|
|
as a trigger must be declared as a function with no arguments
|
|
and a return type of <literal>trigger</>.
|
|
</para>
|
|
<para>
|
|
The information from the trigger manager is passed to the procedure body
|
|
in the following variables:
|
|
|
|
<variablelist>
|
|
|
|
<varlistentry>
|
|
<term><varname>$TG_name</varname></term>
|
|
<listitem>
|
|
<para>
|
|
The name of the trigger from the <command>CREATE TRIGGER</command> statement.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$TG_relid</varname></term>
|
|
<listitem>
|
|
<para>
|
|
The object ID of the table that caused the trigger procedure
|
|
to be invoked.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$TG_relatts</varname></term>
|
|
<listitem>
|
|
<para>
|
|
A Tcl list of the table column names, prefixed with an empty list
|
|
element. So looking up a column name in the list with <application>Tcl</>'s
|
|
<function>lsearch</> command returns the element's number starting
|
|
with 1 for the first column, the same way the columns are customarily
|
|
numbered in <productname>PostgreSQL</productname>. (Empty list
|
|
elements also appear in the positions of columns that have been
|
|
dropped, so that the attribute numbering is correct for columns
|
|
to their right.)
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$TG_when</varname></term>
|
|
<listitem>
|
|
<para>
|
|
The string <literal>BEFORE</> or <literal>AFTER</> depending on the
|
|
type of trigger call.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$TG_level</varname></term>
|
|
<listitem>
|
|
<para>
|
|
The string <literal>ROW</> or <literal>STATEMENT</> depending on the
|
|
type of trigger call.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$TG_op</varname></term>
|
|
<listitem>
|
|
<para>
|
|
The string <literal>INSERT</>, <literal>UPDATE</>, or
|
|
<literal>DELETE</> depending on the type of trigger call.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$NEW</varname></term>
|
|
<listitem>
|
|
<para>
|
|
An associative array containing the values of the new table
|
|
row for <command>INSERT</> or <command>UPDATE</> actions, or
|
|
empty for <command>DELETE</>. The array is indexed by column
|
|
name. Columns that are null will not appear in the array.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$OLD</varname></term>
|
|
<listitem>
|
|
<para>
|
|
An associative array containing the values of the old table
|
|
row for <command>UPDATE</> or <command>DELETE</> actions, or
|
|
empty for <command>INSERT</>. The array is indexed by column
|
|
name. Columns that are null will not appear in the array.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>$args</varname></term>
|
|
<listitem>
|
|
<para>
|
|
A Tcl list of the arguments to the procedure as given in the
|
|
<command>CREATE TRIGGER</command> statement. These arguments are also accessible as
|
|
<literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal> in the procedure body.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</para>
|
|
|
|
<para>
|
|
The return value from a trigger procedure can be one of the strings
|
|
<literal>OK</> or <literal>SKIP</>, or a list as returned by the
|
|
<literal>array get</> Tcl command. If the return value is <literal>OK</>,
|
|
the operation (<command>INSERT</>/<command>UPDATE</>/<command>DELETE</>) that fired the trigger will proceed
|
|
normally. <literal>SKIP</> tells the trigger manager to silently suppress
|
|
the operation for this row. If a list is returned, it tells PL/Tcl to
|
|
return a modified row to the trigger manager that will be inserted
|
|
instead of the one given in <varname>$NEW</>. (This works for <command>INSERT</> and <command>UPDATE</>
|
|
only.) Needless to say that all this is only meaningful when the trigger
|
|
is <literal>BEFORE</> and <command>FOR EACH ROW</>; otherwise the return value is ignored.
|
|
</para>
|
|
<para>
|
|
Here's a little example trigger procedure that forces an integer value
|
|
in a table to keep track of the number of updates that are performed on the
|
|
row. For new rows inserted, the value is initialized to 0 and then
|
|
incremented on every update operation.
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION trigfunc_modcount() RETURNS trigger AS $$
|
|
switch $TG_op {
|
|
INSERT {
|
|
set NEW($1) 0
|
|
}
|
|
UPDATE {
|
|
set NEW($1) $OLD($1)
|
|
incr NEW($1)
|
|
}
|
|
default {
|
|
return OK
|
|
}
|
|
}
|
|
return [array get NEW]
|
|
$$ LANGUAGE pltcl;
|
|
|
|
CREATE TABLE mytab (num integer, description text, modcnt integer);
|
|
|
|
CREATE TRIGGER trig_mytab_modcount BEFORE INSERT OR UPDATE ON mytab
|
|
FOR EACH ROW EXECUTE PROCEDURE trigfunc_modcount('modcnt');
|
|
</programlisting>
|
|
|
|
Notice that the trigger procedure itself does not know the column
|
|
name; that's supplied from the trigger arguments. This lets the
|
|
trigger procedure be reused with different tables.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="pltcl-unknown">
|
|
<title>Modules and the <function>unknown</> command</title>
|
|
<para>
|
|
PL/Tcl has support for autoloading Tcl code when used.
|
|
It recognizes a special table, <literal>pltcl_modules</>, which
|
|
is presumed to contain modules of Tcl code. If this table
|
|
exists, the module <literal>unknown</> is fetched from the table
|
|
and loaded into the Tcl interpreter immediately before the first
|
|
execution of a PL/Tcl function in a database session. (This
|
|
happens separately for each Tcl interpreter, if more than one is
|
|
used in a session; see <xref linkend="pltcl-global">.)
|
|
</para>
|
|
<para>
|
|
While the <literal>unknown</> module could actually contain any
|
|
initialization script you need, it normally defines a Tcl
|
|
<function>unknown</> procedure that is invoked whenever Tcl does
|
|
not recognize an invoked procedure name. <application>PL/Tcl</>'s standard version
|
|
of this procedure tries to find a module in <literal>pltcl_modules</>
|
|
that will define the required procedure. If one is found, it is
|
|
loaded into the interpreter, and then execution is allowed to
|
|
proceed with the originally attempted procedure call. A
|
|
secondary table <literal>pltcl_modfuncs</> provides an index of
|
|
which functions are defined by which modules, so that the lookup
|
|
is reasonably quick.
|
|
</para>
|
|
<para>
|
|
The <productname>PostgreSQL</productname> distribution includes
|
|
support scripts to maintain these tables:
|
|
<command>pltcl_loadmod</>, <command>pltcl_listmod</>,
|
|
<command>pltcl_delmod</>, as well as source for the standard
|
|
<literal>unknown</> module in <filename>share/unknown.pltcl</>. This module
|
|
must be loaded
|
|
into each database initially to support the autoloading mechanism.
|
|
</para>
|
|
<para>
|
|
The tables <literal>pltcl_modules</> and <literal>pltcl_modfuncs</>
|
|
must be readable by all, but it is wise to make them owned and
|
|
writable only by the database administrator. As a security
|
|
precaution, PL/Tcl will ignore <literal>pltcl_modules</> (and thus,
|
|
not attempt to load the <literal>unknown</> module) unless it is
|
|
owned by a superuser. But update privileges on this table can be
|
|
granted to other users, if you trust them sufficiently.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="pltcl-procnames">
|
|
<title>Tcl Procedure Names</title>
|
|
|
|
<para>
|
|
In <productname>PostgreSQL</productname>, one and the
|
|
same function name can be used for
|
|
different functions as long as the number of arguments or their types
|
|
differ. Tcl, however, requires all procedure names to be distinct.
|
|
PL/Tcl deals with this by making the internal Tcl procedure names contain
|
|
the object
|
|
ID of the function from the system table <structname>pg_proc</> as part of their name. Thus,
|
|
<productname>PostgreSQL</productname> functions with the same name
|
|
and different argument types will be different Tcl procedures, too. This
|
|
is not normally a concern for a PL/Tcl programmer, but it might be visible
|
|
when debugging.
|
|
</para>
|
|
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
Local variables:
|
|
mode:sgml
|
|
sgml-omittag:nil
|
|
sgml-shorttag:t
|
|
sgml-minimize-attributes:nil
|
|
sgml-always-quote-attributes:t
|
|
sgml-indent-step:1
|
|
sgml-indent-data:t
|
|
sgml-parent-document:nil
|
|
sgml-default-dtd-file:"./reference.ced"
|
|
sgml-exposed-tags:nil
|
|
sgml-local-catalogs:("/usr/lib/sgml/catalog")
|
|
sgml-local-ecat-files:nil
|
|
End:
|
|
-->
|