INTERSECT
MariaDB starting with 10.3.0
INTERSECT was introduced in MariaDB 10.3.0.
The result of an intersect is the intersection of right and left SELECT
results, i.e. only records that are present in both result sets will be included in the result of the operation.
Syntax
SELECT ... (INTERSECT | EXCEPT | UNION [ALL | DISTINCT]) SELECT ... [(INTERSECT | EXCEPT | UNION [ALL | DISTINCT]) SELECT ...] [ORDER BY [column [, column ...]]] [LIMIT {[offset,] row_count | row_count OFFSET offset}]
Contents
Please note:
- ALL is not supported by
INTERSECT
(and it is difficult to make sense of ALL with INTERSECT). - Brackets for explicit operation precedence are not supported; use a subquery in the
FROM
clause as a workaround).
Description
MariaDB has supported INTERSECT
(as well as EXCEPT) in addition to UNION since MariaDB 10.3.
All behavior for naming columns, ORDER BY
and LIMIT
is the same as for UNION.
INTERSECT
implicitly supposes a DISTINCT
operation.
The result of an intersect is the intersection of right and left SELECT
results, i.e. only records that are present in both result sets will be included in the result of the operation.
INTERSECT
has higher precedence than UNION
and EXCEPT
. If possible it will be executed linearly but if not it will be translated to a subquery in the FROM
clause:
(select a,b from t1) union (select c,d from t2) intersect (select e,f from t3) union (select 4,4);
will be translated to:
(select a,b from t1) union select c,d from ((select c,d from t2) intersect (select e,f from t3)) dummy_subselect union (select 4,4)
MariaDB starting with 10.4.0
Parentheses
From MariaDB 10.4.0, parentheses can be used to specify precedence. Before this, a syntax error would be returned.
Examples
Show customers which are employees:
(SELECT e_name AS name, email FROM employees) INTERSECT (SELECT c_name AS name, email FROM customers);
Difference between UNION, EXCEPT and INTERSECT:
CREATE TABLE seqs (i INT); INSERT INTO seqs VALUES (1),(2),(3),(4),(5),(6); SELECT i FROM seqs WHERE i <= 3 UNION SELECT i FROM seqs WHERE i>=3; +------+ | i | +------+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | +------+ SELECT i FROM seqs WHERE i <= 3 EXCEPT SELECT i FROM seqs WHERE i>=3; +------+ | i | +------+ | 1 | | 2 | +------+ SELECT i FROM seqs WHERE i <= 3 INTERSECT SELECT i FROM seqs WHERE i>=3; +------+ | i | +------+ | 3 | +------+
Parentheses for specifying precedence, from MariaDB 10.4.0
CREATE OR REPLACE TABLE t1 (a INT); CREATE OR REPLACE TABLE t2 (b INT); CREATE OR REPLACE TABLE t3 (c INT); INSERT INTO t1 VALUES (1),(2),(3),(4); INSERT INTO t2 VALUES (5),(6); INSERT INTO t3 VALUES (1),(6); ((SELECT a FROM t1) UNION (SELECT b FROM t2)) INTERSECT (SELECT c FROM t3); +------+ | a | +------+ | 1 | | 6 | +------+ (SELECT a FROM t1) UNION ((SELECT b FROM t2) INTERSECT (SELECT c FROM t3)); +------+ | a | +------+ | 1 | | 2 | | 3 | | 4 | | 6 | +------+