.\" This is -*-nroff-*- .\" XXX standard disclaimer belongs here.... .\" $Header: /cvsroot/pgsql/doc/man/Attic/sql.l,v 1.1.1.1 1996/08/18 22:14:28 scrappy Exp $ .TH INTRODUCTION SQL 11/5/95 Postgres95 Postgres95 .SH "Section 4 \(em SQL Commands (COMMANDS)" .SH "General Information" .SH DESCRIPTION The following is a description of the general syntax of SQL. Individual SQL statements and commands are treated separately in the document; this section describes the syntactic classes from which the constituent parts of SQL statements are drawn. .SH Comments A .IR comment is an arbitrary sequence of characters following double dashes up to the end of the line e.g: .nf -- This is a comment .fi .SH "Names" .IR Names in SQL are sequences of not more than NAMEDATALEN alphanumeric characters, starting with an alphabetic character. By default, NAMEDATALEN is set to 16, but at the time the system is built, NAMEDATALEN can be changed by changing the #ifdef in src/backend/include/postgres.h. Underscore (\*(lq_\*(rq) is considered an alphabetic character. .SH "Keywords" The following identifiers are reserved for use as .IR keywords and may not be used otherwise: .PP .ft B .nf .if n .ta 5 +15 +15 +15 .if t .ta 0.5i +1.5i +1.5i +1.5i .fi .ft .ft B .nf .if n .ta 5 +15 +15 +15 .if t .ta 0.5i +1.5i +1.5i +1.5i .fi .ft .PP In addition, all Postgres classes have several predefined attributes used by the system. .SH "Constants" There are six types of .IR constants for use in SQL. They are described below. .SH "String Constants" .IR Strings in SQL are arbitrary sequences of ASCII characters bounded by single quotes (' '). Uppercase alphabetics within strings are accepted literally. Non-printing characters may be embedded within strings by prepending them with a backslash, e.g., `\en'. Also, in order to embed quotes within strings, it is necessary to prefix them with `\e' . The same convention applies to `\e' itself. Because of the limitations on instance sizes, string constants are currently limited to a length of a little less than 8192 bytes. Larger objects may be created using the Postgres Large Object interface. .SH "Integer Constants" .IR "Integer constants" in SQL are collection of ASCII digits with no decimal point. Legal values range from \(mi2147483647 to +2147483647. This will vary depending on the operating system and host machine. .SH "Floating Point Constants" .IR "Floating point constants" consist of an integer part, a decimal point, and a fraction part or scientific notation of the following format: .nf {} .{} [e [+-] {}] .fi Where is a digit. You must include at least one after the period and after the [+-] if you use those options. An exponent with a missing mantissa has a mantissa of 1 inserted. There may be no extra characters embedded in the string. Floating point constaints are of type float4. .SH "Constants of Postgres User-Defined Types" A constant of an .IR arbitrary type can be entered using the notation: .nf 'string'::type-name .fi or .nf CAST 'string' AS type-name .fi The value inside the string is passed to the input conversion routine for the type called type-name. The result is a constant of the indicated type. The explicit typecast may be omitted if there is no ambiguity as to the type the constant must be, in which case it is automatically coerced. .SH "Array constants" .IR "Array constants" are arrays of any Postgres type, including other arrays, string constants, etc. The general format of an array constant is the following: .nf {} .fi Where .IR "" is the delimiter for the type stored in the \*(lqpg_type\*(rq class. (For built-in types, this is the comma character, \*(lq,\*(rq.) An example of an array constant is .nf {{1,2,3},{4,5,6},{7,8,9}} .fi This constant is a two-dimensional, 3 by 3 array consisting of three sub-arrays of integers. .PP Individual array elements can and should be placed between quotation marks whenever possible to avoid ambiguity problems with respect to leading white space. .\" Elements of single-element arrays (e.g., .\" \*(lq{"1"}\*(rq) must be quoted. .PP .SH "FIELDS AND COLUMNS" .SH "Fields" A .IR field is either an attribute of a given class or one of the following: .nf oid tmin tmax xmin xmax cmin cmax .fi .PP .IR Oid stands for the unique identifier of an instance which is added by Postgres to all instances automatically. Oids are not reused and are 32 bit quantities. .PP .IR "Tmin, tmax, xmin, cmin, xmax" and .IR cmax stand respectively for the time that the instance was inserted, the time the instance was deleted, the identity of the inserting transaction, the command identifier within the transaction, the identity of the deleting transaction and its associated deleting command. For further information on these fields consult [STON87]. Times are represented internally as instances of the \*(lqabstime\*(rq data type. Transaction identifiers are 32 bit quantities which are assigned sequentially starting at 512. Command identifiers are 16 bit objects; hence, it is an error to have more than 65535 SQL commands within one transaction. .SH "Columns" A .IR column is a construct of the form: .nf Instance-variable{.composite_field}.field `['number`]' .fi .IR Instance-variable identifies a particular class and can be thought of as standing for the instances of that class. An instance variable is either a class name, a surrogate for a class defined by means of a .IR from clause, or the keyword .BR new or .BR current. New and current can only appear in the action portion of a rule, while other instance variables can be used in any SQL statement. .IR Composite_field is a field of of one of the Postgres composite types indicated in the .IR information (l) section, while successive composite fields address attributes in the class(s) to which the composite field evaluates. Lastly, .IR field is a normal (base type) field in the class(s) last addressed. If .IR field is of type array, then the optional .IR number designator indicates a specific element in the array. If no number is indicated, then all array elements are returned. .SH "Operators" Any built-in system, or user-defined operator may be used in SQL. For the list of built-in and system operators consult .BR "introduction" "(3)." For a list of user-defined operators consult your system administrator or run a query on the pg_operator class. Parentheses may be used for arbitrary grouping of operators. .SH "Expressions (a_expr)" An .IR expression is one of the following: .nf ( a_expr ) constant attribute a_expr binary_operator a_expr a_expr right_unary_operator left_unary_operator a_expr parameter functional expressions aggregate expressions .fi We have already discussed constants and attributes. The two kinds of operator expressions indicate respectively binary and left_unary expressions. The following sections discuss the remaining options. .SH "Parameters" A .IR parameter is used to indicate a parameter in a SQL function. Typically this is used in SQL function definition statement. The form of a parameter is: .nf \'$' number .fi For example, consider the definition of a function, DEPT, as .nf create function DEPT (char16) returns dept as 'select * from dept where name=$1' language 'sql' .fi .SH "Functional Expressions" A .IR "functional expression" is the name of a legal SQL function, followed by its argument list enclosed in parentheses, e.g.: .nf fn-name (a_expr{ , a_expr}) .fi For example, the following computes the square root of an employee salary. .nf sqrt(emp.salary) .fi .SH "Aggregate Expression" An .IR "aggregate expression" represents a simple aggregate (i.e., one that computes a single value) or an aggregate function (i.e., one that computes a set of values). The syntax is the following: .nf aggregate.name (attribute) .fi Here, .IR aggregate_name must be a previously defined aggregate. .SH "Target_list" A .IR "target list" is a parenthesized, comma-separated list of one or more elements, each of which must be of the form: .nf a_expr[AS result_attname] .fi Here, result_attname is the name of the attribute to be created (or an already existing attribute name in the case of update statements.) If .IR result_attname is not present, then .IR a_expr must contain only one attribute name which is assumed to be the name of the result field. In Postgres default naming is only used if .IR a_expr is an attribute. .SH‚‚ "Qualification" A .IR qualification consists of any number of clauses connected by the logical operators: .nf not and or .fi A clause is an .IR a_expr that evaluates to a Boolean over a set of instances. .SH "From List" The .IR "from list" is a comma-separated list of .IR "from expressions" . .PP Each .IR "from expression" is of the form: .nf [class_reference] instance_variable {, [class_ref] instance_variable...} .fi where .IR class_reference is of the form .nf class_name [time_expression] [*] .fi The .IR "from expression" defines one or more instance variables to range over the class indicated in .IR class_reference . Adding a .IR time_expression will indicate that a historical class is desired. One can also request the instance variable to range over all classes that are beneath the indicated class in the inheritance hierarchy by postpending the designator \*(lq*\*(rq. .SH‚‚ "Time Expressions" A .IR "time expression" is in one of two forms: .nf ['date'] ['date-1', 'date-2'] .fi The first case requires instances that are valid at the indicated time. The second case requires instances that are valid at some time within the date range specified. If no time expression is indicated, the default is \*(lqnow\*(rq. .PP In each case, the date is a character string of the form .nf [MON-FRI] 'MMM DD [HH:MM:SS] YYYY' [Timezone] .fi where MMM is the month (Jan \- Dec), DD is a legal day number in the specified month, HH:MM:SS is an optional time in that day (24-hour clock), and YYYY is the year. If the time of day HH:MM:SS is not specified, it defaults to midnight at the start of the specified day. As of Version 3.0, times are no longer read and written using Greenwich Mean Time; the input and output routines default to the local time zone. .PP For example, .nf ['Jan 1 1990'] ['Mar 3 00:00:00 1980', 'Mar 3 23:59:59 1981r'] .fi are valid time specifications. .PP Note that this syntax is slightly different than that used by the time-range type. .SH "SEE ALSO" insert(l), delete(l), execute(l), update(l), select(l), monitor(1).