A description of the general syntax of SQL. SQL manipulates sets of data. The language is composed of various key words. Arithmetic and procedural expressions are allowed. We will cover these topics in this chapter; subsequent chapters will include details on data types, functions, and operators. SQL92 defines key words for the language which have specific meaning. Some key words are reserved, which indicates that they are restricted to appear in only certain contexts. Other key words are not restricted, which indicates that in certain contexts they have a specific meaning but are not otherwise constrained. Postgres implements an extended subset of the SQL92 and SQL3 languages. Some language elements are not as restricted in this implementation as is called for in the language standards, in part due to the extensibility features of Postgres. Information on SQL92 and SQL3 key words is derived from . SQL92 and SQL3 have reserved key words which are not allowed as identifiers and not allowed in any usage other than as fundamental tokens in SQL statements. Postgres has additional key words which have similar restrictions. In particular, these key words are not allowed as column or table names, though in some cases they are allowed to be column labels (i.e. in AS clauses). Any string can be used as an identifier if surrounded by double quotes (like this!). Some care is required since such an identifier will be case sensitive and will retain embedded whitespace and most other special characters. The following are Postgres reserved words which are neither SQL92 nor SQL3 reserved words. These are allowed to be present as column labels, but not as identifiers: ABORT ANALYZE BINARY CLUSTER CONSTRAINT COPY DO EXPLAIN EXTEND LISTEN LOAD LOCK MOVE NEW NONE NOTIFY OFFSET RESET SETOF SHOW UNLISTEN UNTIL VACUUM VERBOSE The following are Postgres reserved words which are also SQL92 or SQL3 reserved words, and which are allowed to be present as column labels, but not as identifiers: ALL ANY ASC BETWEEN BIT BOTH CASE CAST CHAR CHARACTER CHECK COALESCE COLLATE COLUMN CONSTRAINT CROSS CURRENT CURRENT_DATE CURRENT_TIME CURRENT_TIMESTAMP CURRENT_USER DEC DECIMAL DEFAULT DESC DISTINCT ELSE END EXCEPT EXISTS EXTRACT FALSE FLOAT FOR FOREIGN FROM FULL GLOBAL GROUP HAVING IN INNER INTERSECT INTO IS JOIN LEADING LEFT LIKE LOCAL NATURAL NCHAR NOT NULL NULLIF NUMERIC ON OR ORDER OUTER OVERLAPS POSITION PRECISION PRIMARY PUBLIC REFERENCES RIGHT SELECT SESSION_USER SOME SUBSTRING TABLE THEN TO TRANSACTION TRIM TRUE UNION UNIQUE USER VARCHAR WHEN WHERE The following are Postgres reserved words which are also SQL92 or SQL3 reserved words: ADD ALTER AND AS BEGIN BY CASCADE CLOSE COMMIT CREATE CURSOR DECLARE DEFAULT DELETE DESC DISTINCT DROP EXECUTE EXISTS EXTRACT FETCH FLOAT FOR FROM FULL GRANT HAVING IN INNER INSERT INTERVAL INTO INOUT IS JOIN LEADING LEFT LIKE LOCAL NAMES NATIONAL NATURAL NCHAR NO NOT NULL ON OR OUT OUTER PARTIAL PRIMARY PRIVILEGES PROCEDURE PUBLIC REFERENCES REVOKE RIGHT ROLLBACK SELECT SESSION SET SUBSTRING TO TRAILING TRIM UNION UNIQUE UPDATE USING VALUES VARCHAR VARYING VIEW WHERE WITH WITHOUT WORK The following are SQL92 reserved key words which are not Postgres reserved key words, but which if used as function names are always translated into the function CHAR_LENGTH: CHARACTER_LENGTH The following are SQL92 or SQL3 reserved key words which are not Postgres reserved key words, but if used as type names are always translated into an alternate, native type: BOOLEAN DOUBLE FLOAT INT INTEGER INTERVAL REAL SMALLINT The following are not keywords of any kind, but when used in the context of a type name are translated into a native Postgres type, and when used in the context of a function name are translated into a native function: DATETIME TIMESPAN (translated to TIMESTAMP and INTERVAL, respectively). This feature is intended to help with transitioning to v7.0, and will be removed in the next full release (likely v7.1). The following are either SQL92 or SQL3 reserved key words which are not key words in Postgres. These have no proscribed usage in Postgres at the time of writing (v7.0) but may become reserved key words in the future: Some of these key words represent functions in SQL92. These functions are defined in Postgres, but the parser does not consider the names to be key words and they are allowed in other contexts. ALLOCATE ARE ASSERTION AT AUTHORIZATION AVG BIT_LENGTH CASCADED CATALOG CHAR_LENGTH CHARACTER_LENGTH COLLATION CONNECT CONNECTION CONTINUE CONVERT CORRESPONDING COUNT CURRENT_SESSION DATE DEALLOCATE DEC DESCRIBE DESCRIPTOR DIAGNOSTICS DISCONNECT DOMAIN ESCAPE EXCEPT EXCEPTION EXEC EXTERNAL FIRST FOUND GET GO GOTO IDENTITY INDICATOR INPUT INTERSECT LAST LOWER MAX MIN MODULE OCTET_LENGTH OPEN OUTPUT OVERLAPS PREPARE PRESERVE ROWS SCHEMA SECTION SESSION SIZE SOME SQL SQLCODE SQLERROR SQLSTATE SUM SYSTEM_USER TEMPORARY TRANSLATE TRANSLATION UNKNOWN UPPER USAGE VALUE WHENEVER WRITE SQL92 and SQL3 have non-reserved keywords which have a prescribed meaning in the language but which are also allowed as identifiers. Postgres has additional keywords which allow similar unrestricted usage. In particular, these keywords are allowed as column or table names. The following are Postgres non-reserved key words which are neither SQL92 nor SQL3 non-reserved key words: ACCESS AFTER AGGREGATE BACKWARD BEFORE CACHE COMMENT CREATEDB CREATEUSER CYCLE DATABASE DELIMITERS EACH ENCODING EXCLUSIVE FORCE FORWARD FUNCTION HANDLER INCREMENT INDEX INHERITS INSENSITIVE INSTEAD ISNULL LANCOMPILER LOCATION MAXVALUE MINVALUE MODE NOCREATEDB NOCREATEUSER NOTHING NOTIFY NOTNULL OIDS OPERATOR PASSWORD PROCEDURAL RECIPE REINDEX RENAME RETURNS ROW RULE SEQUENCE SERIAL SHARE START STATEMENT STDIN STDOUT TEMP TRUSTED UNLISTEN UNTIL VALID VERSION The following are Postgres non-reserved key words which are SQL92 or SQL3 reserved key words: ABSOLUTE ACTION CHARACTERISTICS CONSTRAINTS DAY DEFERRABLE DEFERRED HOUR IMMEDIATE INITIALLY INSENSITIVE ISOLATION KEY LANGUAGE LEVEL MATCH MINUTE MONTH NEXT OF ONLY OPTION PATH PENDANT PRIOR PRIVILEGES READ RELATIVE RESTRICT SCHEMA SCROLL SECOND TIME TIMESTAMP TIMEZONE_HOUR TIMEZONE_MINUTE TRIGGER YEAR ZONE The following are Postgres non-reserved key words which are also either SQL92 or SQL3 non-reserved key words: COMMITTED SERIALIZABLE TYPE The following are either SQL92 or SQL3 non-reserved key words which are not key words of any kind in Postgres: ADA C CATALOG_NAME CHARACTER_SET_CATALOG CHARACTER_SET_NAME CHARACTER_SET_SCHEMA CLASS_ORIGIN COBOL COLLATION_CATALOG COLLATION_NAME COLLATION_SCHEMA COLUMN_NAME COMMAND_FUNCTION CONDITION_NUMBER CONNECTION_NAME CONSTRAINT_CATALOG CONSTRAINT_NAME CONSTRAINT_SCHEMA CURSOR_NAME DATA DATE_TIME_INTERVAL_CODE DATE_TIME_INTERVAL_PRECISION DYNAMIC_FUNCTION FORTRAN LENGTH MESSAGE_LENGTH MESSAGE_OCTET_LENGTH MORE MUMPS NAME NULLABLE NUMBER PAD PASCAL PLI REPEATABLE RETURNED_LENGTH RETURNED_OCTET_LENGTH RETURNED_SQLSTATE ROW_COUNT SCALE SCHEMA_NAME SERVER_NAME SPACE SUBCLASS_ORIGIN TABLE_NAME UNCOMMITTED UNNAMED A comment is an arbitrary sequence of characters beginning with double dashes and extending to the end of the line, e.g.: -- This is a standard SQL comment We also support C-style block comments, e.g.: /* multi-line comment * with nesting: /* nested block comment */ */ where the comment begins with "/*" and extends to the matching occurrence of "*/". These block comments nest, as specified in SQL99, so that one can comment out larger blocks of code which may contain existing block comments. Names in SQL must begin with a letter (a-z) or underscore (_). Subsequent characters in a name can be letters, digits (0-9), or underscores. The system uses no more than NAMEDATALEN-1 characters of a name; longer names can be written in queries, but they will be truncated. By default, NAMEDATALEN is 32 so the maximum name length is 31 (but at the time the system is built, NAMEDATALEN can be changed in src/include/postgres_ext.h). Names containing other characters may be formed by surrounding them with double quotes ("). For example, table or column names may contain otherwise disallowed characters such as spaces, ampersands, etc. if quoted. Quoting a name also makes it case-sensitive, whereas unquoted names are always folded to lower case. For example, the names FOO, foo and "foo" are considered the same by Postgres, but "Foo" is a different name. Double quotes can also be used to protect a name that would otherwise be taken to be an SQL keyword. For example, IN is a keyword but "IN" is a name. There are three kinds of implicitly typed constants in Postgres: strings, integers, and floating point numbers. Constants can also be specified with explicit types, which can enable more accurate representation and more efficient handling by the backend. The implicit constants are described below; explicit constants are discussed afterwards. Strings in SQL are arbitrary sequences of ASCII characters bounded by single quotes ("'", e.g. 'This is a string'). SQL92 allows single quotes to be embedded in strings by typing two adjacent single quotes (e.g. 'Dianne''s horse'). In Postgres single quotes may alternatively be escaped with a backslash ("\", e.g. 'Dianne\'s horse'). To include a backslash in a string constant, type two backslashes. Non-printing characters may also be embedded within strings by prepending them with a backslash (e.g. '\tab'). Integer constants in SQL are sequences of ASCII digits with no decimal point. The range of legal values depends on which integer datatype is used, but the plain integer type accepts values ranging from -2147483648 to +2147483647. Floating point constants consist of an integer part, a decimal point, and a fraction part or scientific notation of the following format: {dig}.{dig} [e [+-] {dig}] where dig is one or more digits. You must include at least one dig 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 float8. float4 can be specified explicitly by using SQL92 string notation or Postgres type notation: float4 '1.23' -- string style '1.23'::float4 -- Postgres (historical) style A constant of an arbitrary type can be entered using any one of the following notations: type 'string' 'string'::type CAST ( 'string' AS type ) The value inside the string is passed to the input conversion routine for the type called type. 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. It is also possible to specify a type coercion using a function-like syntax: typename ( value ) although this only works for types whose names are also valid as function names. (For example, double precision can't be used this way --- but the equivalent float8 can.) The ::, CAST(), and function-call syntaxes can also be used to specify run-time type conversions. But the form type 'string' can only be used to specify the type of a literal constant. Array constants are n-dimensional arrays of any Postgres datatype. The general format of an array constant is the following: { val1 delim val2 delim ... } where delim is the delimiter character for the type, as recorded in its pg_type class entry. (For all built-in types, this is the comma character ",".) Each val is either a constant of the array element type, or a sub-array. An example of an array constant is {{1,2,3},{4,5,6},{7,8,9}} This constant is a two-dimensional, 3 by 3 array consisting of three sub-arrays of integers. Individual array elements can be placed between single-quote marks to avoid ambiguity problems with respect to leading white space. Without quote marks, the array-value parser will skip white space. Note that to write a quote mark inside a string literal that is to become an array value, you must double the quote mark as described previously. A field is either a user-defined attribute of a given class or one of the following system-defined attributes: 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. xmin The identity of the inserting transaction. xmax The identity of the deleting transaction. cmin The command identifier within the inserting transaction. cmax The command identifier within the deleting transaction. For further information on the system attributes consult . Transaction and command identifiers are 32 bit quantities. A column is a construct of the form: instance{.composite_field}.field `['subscript`]' instance 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, an alias for a class defined by means of a FROM clause, or the keyword NEW or OLD. (NEW and OLD can only appear in the action portion of a rule, while other instance variables can be used in any SQL statement.) The instance name can be omitted if the first field name is unique across all the classes being used in the current query. composite_field is a field of of one of the Postgres composite types, while successive composite fields select attributes in the class(s) to which the composite field evaluates. Lastly, field is a normal (base type) field in the class(s) last addressed. If field is of an array type, then the optional subscript selects a specific element in the array. If no subscript is provided, then the whole array is selected. Any built-in or user-defined operator may be used in SQL. For the list of built-in operators consult . 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 in expressions. SQL92 allows expressions to transform data in tables. Expressions may contain operators and functions. An expression is one of the following: constant column expression binary_operator expression expression right_unary_operator left_unary_operator expression ( expression ) parameter functional expression aggregate expression We have already discussed constants and columns. The three kinds of operator expressions indicate respectively binary (infix), right-unary (suffix) and left-unary (prefix) operators. The following sections discuss the remaining options. A parameter is used to indicate a parameter in a SQL function. Typically this is used in SQL function definition statements. The form of a parameter is: $number For example, consider the definition of a function, dept, as CREATE FUNCTION dept (name) RETURNS dept AS 'select * from dept where name = $1' LANGUAGE 'sql'; A functional expression is the name of a legal SQL function, followed by its argument list enclosed in parentheses: function (expression [, expression ... ] ) For example, the following computes the square root of an employee salary: sqrt(emp.salary) An aggregate expression represents the application of an aggregate function across the rows selected by a query. An aggregate function reduces multiple inputs to a single output value, such as the sum or average of the inputs. The syntax of an aggregate expression is one of the following: aggregate_name (expression) aggregate_name (ALL expression) aggregate_name (DISTINCT expression) aggregate_name ( * ) where aggregate_name is a previously defined aggregate, and expression is any expression that doesn't itself contain an aggregate expression. The first form of aggregate expression invokes the aggregate across all input rows for which the given expression yields a non-null value. The second form is the same as the first, since ALL is the default. The third form invokes the aggregate for all distinct non-null values of the expression found in the input rows. The last form invokes the aggregate once for each input row regardless of null or non-null values; since no particular input value is specified, it is generally only useful for the count() aggregate. For example, count(*) yields the total number of input rows; count(f1) yields the number of input rows in which f1 is non-null; count(distinct f1) yields the number of distinct non-null values of f1. A target list is a comma-separated list of one or more elements, each of which must be of the form: expression [ AS result_attname ] where result_attname is the name to be assigned to the created column. If result_attname is not present, then Postgres selects a default name based on the contents of expression. If expression is a simple attribute reference then the default name will be the same as that attribute's name, but otherwise the implementation is free to assign any default name. A qualification consists of any number of clauses connected by the logical operators: NOT AND OR A clause is an expression that evaluates to a boolean over a set of instances. The from list is a comma-separated list of from-expressions. The simplest possibility for a from-expression is: class_reference [ [ AS ] alias ] where class_reference is of the form [ ONLY ] table_name [ * ] The from-expression defines an instance variable that ranges over the rows of the specified table. The instance variable's name is either the table name, or the alias if one is given. Ordinarily, if the table has child tables then the instance variable will range over all rows in the inheritance hierarchy starting with the specified table. If ONLY is specified then child tables are not included. A trailing asterisk * can be written to specifically indicate that child tables are included (ONLY and * are mutually exclusive). A from-expression can also be a sub-query: ( select-statement ) [ AS ] alias Here, the effect is as though the SELECT were executed and its results stored in a temporary table, which then becomes available as an instance variable under the given alias. Finally, a from-expression can be built up from simpler from-expressions using JOIN clauses: from_expression [ NATURAL ] join_type from_expression [ ON join_condition | USING ( join_column_list ) ] This syntax allows specification of outer joins. For details see the reference page for SELECT. The precedence and associativity of the operators is hard-wired into the parser. Most operators have the same precedence and are left-associative. This may lead to non-intuitive behavior; for example the boolean operators "<" and ">" have a different precedence than the boolean operators "<=" and ">=". Also, you will sometimes need to add parentheses when using combinations of binary and unary operators. For instance SELECT 5 & ~ 6; will be parsed as SELECT (5 &) ~ 6; because the parser has no idea that & is defined as a binary operator. This is the price one pays for extensibility. OperatorElement Associativity Description :: left Postgres-style typecast [ ] left array element selection . left table/column name separator - right unary minus ^ left exponentiation * / % left multiplication, division, modulo + - left addition, subtraction IS test for TRUE, FALSE, NULL ISNULL test for NULL NOTNULL test for NOT NULL (any other) left all other native and user-defined operators IN set membership BETWEEN containment OVERLAPS time interval overlap LIKE ILIKE string pattern matching < > less than, greater than = right equality, assignment NOT right logical negation AND left logical conjunction OR left logical disjunction Note that the operator precedence rules also apply to user-defined operators that have the same names as the built-in operators mentioned above. For example, if you define a + operator for some custom data type it will have the same precedence as the built-in + operator, no matter what yours does.