1SELECT() SQL Commands SELECT()
2
6 SELECT - retrieve rows from a table or view
7
10 SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
11 * | expression [ AS output_name ] [, ...]
12 [ FROM from_item [, ...] ]
13 [ WHERE condition ]
14 [ GROUP BY expression [, ...] ]
15 [ HAVING condition [, ...] ]
16 [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]
17 [ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
18 [ LIMIT { count | ALL } ]
19 [ OFFSET start ]
20 [ FOR { UPDATE | SHARE } [ OF table_name [, ...] ] [ NOWAIT ] [...] ]
21 where from_item can be one of:
23 [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
25 ( select ) [ AS ] alias [ ( column_alias [, ...] ) ]
26 function_name ( [ argument [, ...] ] ) [ AS ] alias [ ( column_alias [, ...] | column_definition [, ...] ) ]
27 function_name ( [ argument [, ...] ] ) AS ( column_definition [, ...] )
28 from_item [ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ]
29
32 SELECT retrieves rows from zero or more tables. The general processing
33 of SELECT is as follows:
34 1. All elements in the FROM list are computed. (Each element in
36 the FROM list is a real or virtual table.) If more than one ele‐
37 ment is specified in the FROM list, they are cross-joined
38 together. (See FROM Clause [select(7)] below.)
39 2. If the WHERE clause is specified, all rows that do not satisfy
41 the condition are eliminated from the output. (See WHERE Clause
42 [select(7)] below.)
43 3. If the GROUP BY clause is specified, the output is divided into
45 groups of rows that match on one or more values. If the HAVING
46 clause is present, it eliminates groups that do not satisfy the
47 given condition. (See GROUP BY Clause [select(7)] and HAVING
48 Clause [select(7)] below.)
49 4. The actual output rows are computed using the SELECT output
51 expressions for each selected row. (See SELECT List [select(7)]
52 below.)
53 5. Using the operators UNION, INTERSECT, and EXCEPT, the output of
55 more than one SELECT statement can be combined to form a single
56 result set. The UNION operator returns all rows that are in one
57 or both of the result sets. The INTERSECT operator returns all
58 rows that are strictly in both result sets. The EXCEPT operator
59 returns the rows that are in the first result set but not in the
60 second. In all three cases, duplicate rows are eliminated unless
61 ALL is specified. (See UNION Clause [select(7)], INTERSECT
62 Clause [select(l)], and EXCEPT Clause [select(7)] below.)
63 6. If the ORDER BY clause is specified, the returned rows are
65 sorted in the specified order. If ORDER BY is not given, the
66 rows are returned in whatever order the system finds fastest to
67 produce. (See ORDER BY Clause [select(7)] below.)
68 7. DISTINCT eliminates duplicate rows from the result. DISTINCT ON
70 eliminates rows that match on all the specified expressions. ALL
71 (the default) will return all candidate rows, including dupli‐
72 cates. (See DISTINCT Clause [select(7)] below.)
73 8. If the LIMIT or OFFSET clause is specified, the SELECT statement
75 only returns a subset of the result rows. (See LIMIT Clause
76 [select(7)] below.)
77 9. If FOR UPDATE or FOR SHARE is specified, the SELECT statement
79 locks the selected rows against concurrent updates. (See FOR
80 UPDATE/FOR SHARE Clause [select(7)] below.)
81 You must have SELECT privilege on a table to read its values. The use
83 of FOR UPDATE or FOR SHARE requires UPDATE privilege as well.
84
86 FROM CLAUSE
87 The FROM clause specifies one or more source tables for the SELECT. If
88 multiple sources are specified, the result is the Cartesian product
89 (cross join) of all the sources. But usually qualification conditions
90 are added to restrict the returned rows to a small subset of the Carte‐
91 sian product.
92 The FROM clause can contain the following elements:
94 table_name
96 The name (optionally schema-qualified) of an existing table or
97 view. If ONLY is specified, only that table is scanned. If ONLY
98 is not specified, the table and all its descendant tables (if
99 any) are scanned. * can be appended to the table name to indi‐
100 cate that descendant tables are to be scanned, but in the cur‐
101 rent version, this is the default behavior. (In releases before
102 7.1, ONLY was the default behavior.) The default behavior can be
103 modified by changing the sql_inheritance configuration option.
104 alias A substitute name for the FROM item containing the alias. An
106 alias is used for brevity or to eliminate ambiguity for self-
107 joins (where the same table is scanned multiple times). When an
108 alias is provided, it completely hides the actual name of the
109 table or function; for example given FROM foo AS f, the remain‐
110 der of the SELECT must refer to this FROM item as f not foo. If
111 an alias is written, a column alias list can also be written to
112 provide substitute names for one or more columns of the table.
113 select A sub-SELECT can appear in the FROM clause. This acts as though
115 its output were created as a temporary table for the duration of
116 this single SELECT command. Note that the sub-SELECT must be
117 surrounded by parentheses, and an alias must be provided for it.
118 A VALUES [values(7)] command can also be used here.
119 function_name
121 Function calls can appear in the FROM clause. (This is espe‐
122 cially useful for functions that return result sets, but any
123 function can be used.) This acts as though its output were cre‐
124 ated as a temporary table for the duration of this single SELECT
125 command. An alias may also be used. If an alias is written, a
126 column alias list can also be written to provide substitute
127 names for one or more attributes of the function's composite
128 return type. If the function has been defined as returning the
129 record data type, then an alias or the key word AS must be
130 present, followed by a column definition list in the form ( col‐
131 umn_name data_type [, ... ] ). The column definition list must
132 match the actual number and types of columns returned by the
133 function.
134 join_type
136 One of
137 · [ INNER ] JOIN
139 · LEFT [ OUTER ] JOIN
141 · RIGHT [ OUTER ] JOIN
143 · FULL [ OUTER ] JOIN
145 · CROSS JOIN
147 For the INNER and OUTER join types, a join condition must be specified,
149 namely exactly one of NATURAL, ON join_condition, or USING (join_column
150 [, ...]). See below for the meaning. For CROSS JOIN, none of these
151 clauses may appear.
152 A JOIN clause combines two FROM items. Use parentheses if necessary to
154 determine the order of nesting. In the absence of parentheses, JOINs
155 nest left-to-right. In any case JOIN binds more tightly than the commas
156 separating FROM items.
157 CROSS JOIN and INNER JOIN produce a simple Cartesian product, the same
159 result as you get from listing the two items at the top level of FROM,
160 but restricted by the join condition (if any). CROSS JOIN is equiva‐
161 lent to INNER JOIN ON (TRUE), that is, no rows are removed by qualifi‐
162 cation. These join types are just a notational convenience, since they
163 do nothing you couldn't do with plain FROM and WHERE.
164 LEFT OUTER JOIN returns all rows in the qualified Cartesian product
166 (i.e., all combined rows that pass its join condition), plus one copy
167 of each row in the left-hand table for which there was no right-hand
168 row that passed the join condition. This left-hand row is extended to
169 the full width of the joined table by inserting null values for the
170 right-hand columns. Note that only the JOIN clause's own condition is
171 considered while deciding which rows have matches. Outer conditions are
172 applied afterwards.
173 Conversely, RIGHT OUTER JOIN returns all the joined rows, plus one row
175 for each unmatched right-hand row (extended with nulls on the left).
176 This is just a notational convenience, since you could convert it to a
177 LEFT OUTER JOIN by switching the left and right inputs.
178 FULL OUTER JOIN returns all the joined rows, plus one row for each
180 unmatched left-hand row (extended with nulls on the right), plus one
181 row for each unmatched right-hand row (extended with nulls on the
182 left).
183 ON join_condition
185 join_condition is an expression resulting in a value of type
186 boolean (similar to a WHERE clause) that specifies which rows in
187 a join are considered to match.
188 USING (join_column [, ...])
190 A clause of the form USING ( a, b, ... ) is shorthand for ON
191 left_table.a = right_table.a AND left_table.b = right_table.b
192 .... Also, USING implies that only one of each pair of equiva‐
193 lent columns will be included in the join output, not both.
194 NATURAL
196 NATURAL is shorthand for a USING list that mentions all columns
197 in the two tables that have the same names.
198 WHERE CLAUSE
200 The optional WHERE clause has the general form
201 WHERE condition
203 where condition is any expression that evaluates to a result of type
205 boolean. Any row that does not satisfy this condition will be elimi‐
206 nated from the output. A row satisfies the condition if it returns true
207 when the actual row values are substituted for any variable references.
208 GROUP BY CLAUSE
210 The optional GROUP BY clause has the general form
211 GROUP BY expression [, ...]
213 GROUP BY will condense into a single row all selected rows that share
216 the same values for the grouped expressions. expression can be an input
217 column name, or the name or ordinal number of an output column (SELECT
218 list item), or an arbitrary expression formed from input-column values.
219 In case of ambiguity, a GROUP BY name will be interpreted as an input-
220 column name rather than an output column name.
221 Aggregate functions, if any are used, are computed across all rows mak‐
223 ing up each group, producing a separate value for each group (whereas
224 without GROUP BY, an aggregate produces a single value computed across
225 all the selected rows). When GROUP BY is present, it is not valid for
226 the SELECT list expressions to refer to ungrouped columns except within
227 aggregate functions, since there would be more than one possible value
228 to return for an ungrouped column.
229 HAVING CLAUSE
231 The optional HAVING clause has the general form
232 HAVING condition
234 where condition is the same as specified for the WHERE clause.
236 HAVING eliminates group rows that do not satisfy the condition. HAVING
238 is different from WHERE: WHERE filters individual rows before the
239 application of GROUP BY, while HAVING filters group rows created by
240 GROUP BY. Each column referenced in condition must unambiguously refer‐
241 ence a grouping column, unless the reference appears within an aggre‐
242 gate function.
243 The presence of HAVING turns a query into a grouped query even if there
245 is no GROUP BY clause. This is the same as what happens when the query
246 contains aggregate functions but no GROUP BY clause. All the selected
247 rows are considered to form a single group, and the SELECT list and
248 HAVING clause can only reference table columns from within aggregate
249 functions. Such a query will emit a single row if the HAVING condition
250 is true, zero rows if it is not true.
251 SELECT LIST
253 The SELECT list (between the key words SELECT and FROM) specifies
254 expressions that form the output rows of the SELECT statement. The
255 expressions can (and usually do) refer to columns computed in the FROM
256 clause. Using the clause AS output_name, another name can be specified
257 for an output column. This name is primarily used to label the column
258 for display. It can also be used to refer to the column's value in
259 ORDER BY and GROUP BY clauses, but not in the WHERE or HAVING clauses;
260 there you must write out the expression instead.
261 Instead of an expression, * can be written in the output list as a
263 shorthand for all the columns of the selected rows. Also, one can write
264 table_name.* as a shorthand for the columns coming from just that ta‐
265 ble.
266 UNION CLAUSE
268 The UNION clause has this general form:
269 select_statement UNION [ ALL ] select_statement
271 select_statement is any SELECT statement without an ORDER BY, LIMIT,
273 FOR UPDATE, or FOR SHARE clause. (ORDER BY and LIMIT can be attached
274 to a subexpression if it is enclosed in parentheses. Without parenthe‐
275 ses, these clauses will be taken to apply to the result of the UNION,
276 not to its right-hand input expression.)
277 The UNION operator computes the set union of the rows returned by the
279 involved SELECT statements. A row is in the set union of two result
280 sets if it appears in at least one of the result sets. The two SELECT
281 statements that represent the direct operands of the UNION must produce
282 the same number of columns, and corresponding columns must be of com‐
283 patible data types.
284 The result of UNION does not contain any duplicate rows unless the ALL
286 option is specified. ALL prevents elimination of duplicates. (There‐
287 fore, UNION ALL is usually significantly quicker than UNION; use ALL
288 when you can.)
289 Multiple UNION operators in the same SELECT statement are evaluated
291 left to right, unless otherwise indicated by parentheses.
292 Currently, FOR UPDATE and FOR SHARE may not be specified either for a
294 UNION result or for any input of a UNION.
295 INTERSECT CLAUSE
297 The INTERSECT clause has this general form:
298 select_statement INTERSECT [ ALL ] select_statement
300 select_statement is any SELECT statement without an ORDER BY, LIMIT,
302 FOR UPDATE, or FOR SHARE clause.
303 The INTERSECT operator computes the set intersection of the rows
305 returned by the involved SELECT statements. A row is in the intersec‐
306 tion of two result sets if it appears in both result sets.
307 The result of INTERSECT does not contain any duplicate rows unless the
309 ALL option is specified. With ALL, a row that has m duplicates in the
310 left table and n duplicates in the right table will appear min(m,n)
311 times in the result set.
312 Multiple INTERSECT operators in the same SELECT statement are evaluated
314 left to right, unless parentheses dictate otherwise. INTERSECT binds
315 more tightly than UNION. That is, A UNION B INTERSECT C will be read as
316 A UNION (B INTERSECT C).
317 Currently, FOR UPDATE and FOR SHARE may not be specified either for an
319 INTERSECT result or for any input of an INTERSECT.
320 EXCEPT CLAUSE
322 The EXCEPT clause has this general form:
323 select_statement EXCEPT [ ALL ] select_statement
325 select_statement is any SELECT statement without an ORDER BY, LIMIT,
327 FOR UPDATE, or FOR SHARE clause.
328 The EXCEPT operator computes the set of rows that are in the result of
330 the left SELECT statement but not in the result of the right one.
331 The result of EXCEPT does not contain any duplicate rows unless the ALL
333 option is specified. With ALL, a row that has m duplicates in the left
334 table and n duplicates in the right table will appear max(m-n,0) times
335 in the result set.
336 Multiple EXCEPT operators in the same SELECT statement are evaluated
338 left to right, unless parentheses dictate otherwise. EXCEPT binds at
339 the same level as UNION.
340 Currently, FOR UPDATE and FOR SHARE may not be specified either for an
342 EXCEPT result or for any input of an EXCEPT.
343 ORDER BY CLAUSE
345 The optional ORDER BY clause has this general form:
346 ORDER BY expression [ ASC | DESC | USING operator ] [, ...]
348 expression can be the name or ordinal number of an output column
350 (SELECT list item), or it can be an arbitrary expression formed from
351 input-column values.
352 The ORDER BY clause causes the result rows to be sorted according to
354 the specified expressions. If two rows are equal according to the left‐
355 most expression, the are compared according to the next expression and
356 so on. If they are equal according to all specified expressions, they
357 are returned in an implementation-dependent order.
358 The ordinal number refers to the ordinal (left-to-right) position of
360 the result column. This feature makes it possible to define an ordering
361 on the basis of a column that does not have a unique name. This is
362 never absolutely necessary because it is always possible to assign a
363 name to a result column using the AS clause.
364 It is also possible to use arbitrary expressions in the ORDER BY
366 clause, including columns that do not appear in the SELECT result list.
367 Thus the following statement is valid:
368 SELECT name FROM distributors ORDER BY code;
370 A limitation of this feature is that an ORDER BY clause applying to the
372 result of a UNION, INTERSECT, or EXCEPT clause may only specify an out‐
373 put column name or number, not an expression.
374 If an ORDER BY expression is a simple name that matches both a result
376 column name and an input column name, ORDER BY will interpret it as the
377 result column name. This is the opposite of the choice that GROUP BY
378 will make in the same situation. This inconsistency is made to be com‐
379 patible with the SQL standard.
380 Optionally one may add the key word ASC (ascending) or DESC (descend‐
382 ing) after any expression in the ORDER BY clause. If not specified, ASC
383 is assumed by default. Alternatively, a specific ordering operator name
384 may be specified in the USING clause. ASC is usually equivalent to
385 USING < and DESC is usually equivalent to USING >. (But the creator of
386 a user-defined data type can define exactly what the default sort
387 ordering is, and it might correspond to operators with other names.)
388 The null value sorts higher than any other value. In other words, with
390 ascending sort order, null values sort at the end, and with descending
391 sort order, null values sort at the beginning.
392 Character-string data is sorted according to the locale-specific colla‐
394 tion order that was established when the database cluster was initial‐
395 ized.
396 DISTINCT CLAUSE
398 If DISTINCT is specified, all duplicate rows are removed from the
399 result set (one row is kept from each group of duplicates). ALL speci‐
400 fies the opposite: all rows are kept; that is the default.
401 DISTINCT ON ( expression [, ...] ) keeps only the first row of each set
403 of rows where the given expressions evaluate to equal. The DISTINCT ON
404 expressions are interpreted using the same rules as for ORDER BY (see
405 above). Note that the ``first row'' of each set is unpredictable unless
406 ORDER BY is used to ensure that the desired row appears first. For
407 example,
408 SELECT DISTINCT ON (location) location, time, report
410 FROM weather_reports
411 ORDER BY location, time DESC;
412 retrieves the most recent weather report for each location. But if we
414 had not used ORDER BY to force descending order of time values for each
415 location, we'd have gotten a report from an unpredictable time for each
416 location.
417 The DISTINCT ON expression(s) must match the leftmost ORDER BY expres‐
419 sion(s). The ORDER BY clause will normally contain additional expres‐
420 sion(s) that determine the desired precedence of rows within each DIS‐
421 TINCT ON group.
422 LIMIT CLAUSE
424 The LIMIT clause consists of two independent sub-clauses:
425 LIMIT { count | ALL }
427 OFFSET start
428 count specifies the maximum number of rows to return, while start spec‐
430 ifies the number of rows to skip before starting to return rows. When
431 both are specified, start rows are skipped before starting to count the
432 count rows to be returned.
433 When using LIMIT, it is a good idea to use an ORDER BY clause that con‐
435 strains the result rows into a unique order. Otherwise you will get an
436 unpredictable subset of the query's rows — you may be asking for the
437 tenth through twentieth rows, but tenth through twentieth in what
438 ordering? You don't know what ordering unless you specify ORDER BY.
439 The query planner takes LIMIT into account when generating a query
441 plan, so you are very likely to get different plans (yielding different
442 row orders) depending on what you use for LIMIT and OFFSET. Thus, using
443 different LIMIT/OFFSET values to select different subsets of a query
444 result will give inconsistent results unless you enforce a predictable
445 result ordering with ORDER BY. This is not a bug; it is an inherent
446 consequence of the fact that SQL does not promise to deliver the
447 results of a query in any particular order unless ORDER BY is used to
448 constrain the order.
449 FOR UPDATE/FOR SHARE CLAUSE
451 The FOR UPDATE clause has this form:
452 FOR UPDATE [ OF table_name [, ...] ] [ NOWAIT ]
454 The closely related FOR SHARE clause has this form:
457 FOR SHARE [ OF table_name [, ...] ] [ NOWAIT ]
459 FOR UPDATE causes the rows retrieved by the SELECT statement to be
462 locked as though for update. This prevents them from being modified or
463 deleted by other transactions until the current transaction ends. That
464 is, other transactions that attempt UPDATE, DELETE, or SELECT FOR
465 UPDATE of these rows will be blocked until the current transaction
466 ends. Also, if an UPDATE, DELETE, or SELECT FOR UPDATE from another
467 transaction has already locked a selected row or rows, SELECT FOR
468 UPDATE will wait for the other transaction to complete, and will then
469 lock and return the updated row (or no row, if the row was deleted).
470 For further discussion see in the documentation.
471 To prevent the operation from waiting for other transactions to commit,
473 use the NOWAIT option. SELECT FOR UPDATE NOWAIT reports an error,
474 rather than waiting, if a selected row cannot be locked immediately.
475 Note that NOWAIT applies only to the row-level lock(s) — the required
476 ROW SHARE table-level lock is still taken in the ordinary way (see in
477 the documentation). You can use the NOWAIT option of LOCK [lock(7)] if
478 you need to acquire the table-level lock without waiting.
479 FOR SHARE behaves similarly, except that it acquires a shared rather
481 than exclusive lock on each retrieved row. A shared lock blocks other
482 transactions from performing UPDATE, DELETE, or SELECT FOR UPDATE on
483 these rows, but it does not prevent them from performing SELECT FOR
484 SHARE.
485 If specific tables are named in FOR UPDATE or FOR SHARE, then only rows
487 coming from those tables are locked; any other tables used in the
488 SELECT are simply read as usual. A FOR UPDATE or FOR SHARE clause with‐
489 out a table list affects all tables used in the command. If FOR UPDATE
490 or FOR SHARE is applied to a view or sub-query, it affects all tables
491 used in the view or sub-query.
492 Multiple FOR UPDATE and FOR SHARE clauses can be written if it is nec‐
494 essary to specify different locking behavior for different tables. If
495 the same table is mentioned (or implicitly affected) by both FOR UPDATE
496 and FOR SHARE clauses, then it is processed as FOR UPDATE. Similarly, a
497 table is processed as NOWAIT if that is specified in any of the clauses
498 affecting it.
499 FOR UPDATE and FOR SHARE cannot be used in contexts where returned rows
501 can't be clearly identified with individual table rows; for example
502 they can't be used with aggregation.
503 Caution: Avoid locking a row and then modifying it within a
505 later savepoint or PL/pgSQL exception block. A subsequent roll‐
506 back would cause the lock to be lost. For example,
507 BEGIN;
509 SELECT * FROM mytable WHERE key = 1 FOR UPDATE;
510 SAVEPOINT s;
511 UPDATE mytable SET ... WHERE key = 1;
512 ROLLBACK TO s;
513 After the ROLLBACK, the row is effectively unlocked, rather than
515 returned to its pre-savepoint state of being locked but not mod‐
516 ified. This hazard occurs if a row locked in the current trans‐
517 action is updated or deleted, or if a shared lock is upgraded to
518 exclusive: in all these cases, the former lock state is forgot‐
519 ten. If the transaction is then rolled back to a state between
520 the original locking command and the subsequent change, the row
521 will appear not to be locked at all. This is an implementation
522 deficiency which will be addressed in a future release of Post‐
523 greSQL.
524 Caution: It is possible for a SELECT command using both LIMIT
527 and FOR UPDATE/SHARE clauses to return fewer rows than specified
528 by LIMIT. This is because LIMIT is applied first. The command
529 selects the specified number of rows, but might then block try‐
530 ing to obtain lock on one or more of them. Once the SELECT
531 unblocks, the row might have been deleted or updated so that it
532 does not meet the query WHERE condition anymore, in which case
533 it will not be returned.
534
537 To join the table films with the table distributors:
538 SELECT f.title, f.did, d.name, f.date_prod, f.kind
540 FROM distributors d, films f
541 WHERE f.did = d.did
542 title | did | name | date_prod | kind
544 -------------------+-----+--------------+------------+----------
545 The Third Man | 101 | British Lion | 1949-12-23 | Drama
546 The African Queen | 101 | British Lion | 1951-08-11 | Romantic
547 ...
548 To sum the column len of all films and group the results by kind:
551 SELECT kind, sum(len) AS total FROM films GROUP BY kind;
553 kind | total
555 ----------+-------
556 Action | 07:34
557 Comedy | 02:58
558 Drama | 14:28
559 Musical | 06:42
560 Romantic | 04:38
561 To sum the column len of all films, group the results by kind and show
564 those group totals that are less than 5 hours:
565 SELECT kind, sum(len) AS total
567 FROM films
568 GROUP BY kind
569 HAVING sum(len) < interval '5 hours';
570 kind | total
572 ----------+-------
573 Comedy | 02:58
574 Romantic | 04:38
575 The following two examples are identical ways of sorting the individual
578 results according to the contents of the second column (name):
579 SELECT * FROM distributors ORDER BY name;
581 SELECT * FROM distributors ORDER BY 2;
582 did | name
584 -----+------------------
585 109 | 20th Century Fox
586 110 | Bavaria Atelier
587 101 | British Lion
588 107 | Columbia
589 102 | Jean Luc Godard
590 113 | Luso films
591 104 | Mosfilm
592 103 | Paramount
593 106 | Toho
594 105 | United Artists
595 111 | Walt Disney
596 112 | Warner Bros.
597 108 | Westward
598 The next example shows how to obtain the union of the tables distribu‐
601 tors and actors, restricting the results to those that begin with the
602 letter W in each table. Only distinct rows are wanted, so the key word
603 ALL is omitted.
604 distributors: actors:
606 did | name id | name
607 -----+-------------- ----+----------------
608 108 | Westward 1 | Woody Allen
609 111 | Walt Disney 2 | Warren Beatty
610 112 | Warner Bros. 3 | Walter Matthau
611 ... ...
612 SELECT distributors.name
614 FROM distributors
615 WHERE distributors.name LIKE 'W%'
616 UNION
617 SELECT actors.name
618 FROM actors
619 WHERE actors.name LIKE 'W%';
620 name
622 ----------------
623 Walt Disney
624 Walter Matthau
625 Warner Bros.
626 Warren Beatty
627 Westward
628 Woody Allen
629 This example shows how to use a function in the FROM clause, both with
632 and without a column definition list:
633 CREATE FUNCTION distributors(int) RETURNS SETOF distributors AS $$
635 SELECT * FROM distributors WHERE did = $1;
636 $$ LANGUAGE SQL;
637 SELECT * FROM distributors(111);
639 did | name
640 -----+-------------
641 111 | Walt Disney
642 CREATE FUNCTION distributors_2(int) RETURNS SETOF record AS $$
644 SELECT * FROM distributors WHERE did = $1;
645 $$ LANGUAGE SQL;
646 SELECT * FROM distributors_2(111) AS (f1 int, f2 text);
648 f1 | f2
649 -----+-------------
650 111 | Walt Disney
651
654 Of course, the SELECT statement is compatible with the SQL standard.
655 But there are some extensions and some missing features.
656 OMITTED FROM CLAUSES
658 PostgreSQL allows one to omit the FROM clause. It has a straightforward
659 use to compute the results of simple expressions:
660 SELECT 2+2;
662 ?column?
664 ----------
665 4
666 Some other SQL databases cannot do this except by introducing a dummy
668 one-row table from which to do the SELECT.
669 Note that if a FROM clause is not specified, the query cannot reference
671 any database tables. For example, the following query is invalid:
672 SELECT distributors.* WHERE distributors.name = 'Westward';
674 PostgreSQL releases prior to 8.1 would accept queries of this form, and
676 add an implicit entry to the query's FROM clause for each table refer‐
677 enced by the query. This is no longer the default behavior, because it
678 does not comply with the SQL standard, and is considered by many to be
679 error-prone. For compatibility with applications that rely on this
680 behavior the add_missing_from configuration variable can be enabled.
681 THE AS KEY WORD
683 In the SQL standard, the optional key word AS is just noise and can be
684 omitted without affecting the meaning. The PostgreSQL parser requires
685 this key word when renaming output columns because the type extensibil‐
686 ity features lead to parsing ambiguities without it. AS is optional in
687 FROM items, however.
688 NAMESPACE AVAILABLE TO GROUP BY AND ORDER BY
690 In the SQL-92 standard, an ORDER BY clause may only use result column
691 names or numbers, while a GROUP BY clause may only use expressions
692 based on input column names. PostgreSQL extends each of these clauses
693 to allow the other choice as well (but it uses the standard's interpre‐
694 tation if there is ambiguity). PostgreSQL also allows both clauses to
695 specify arbitrary expressions. Note that names appearing in an expres‐
696 sion will always be taken as input-column names, not as result-column
697 names.
698 SQL:1999 and later use a slightly different definition which is not
700 entirely upward compatible with SQL-92. In most cases, however, Post‐
701 greSQL will interpret an ORDER BY or GROUP BY expression the same way
702 SQL:1999 does.
703 NONSTANDARD CLAUSES
705 The clauses DISTINCT ON, LIMIT, and OFFSET are not defined in the SQL
706 standard.
707SQL - Language Statements 2008-06-08 SELECT()