Combine results from multiple SELECT statements into a single result set. This operator can optionally remove duplicates or include all rows.
UNION is used to combine the results from multiple SELECT statements into a single result set.
UNION is used to combine the results from multiple statements into a single result set.
The column names from the first SELECT statement are used as the column names for the results returned. Selected columns listed in corresponding positions of each SELECT statement should have the same data type. (For example, the first column selected by the first statement should have the same type as the first column selected by the other statements.)
If they don't, the type and length of the columns in the result take into account the values returned by all of the SELECTs, so there is no need for explicit casting. Note that currently this is not the case for - see .
Table names can be specified as db_name.tbl_name. This permits writing UNIONs which involve multiple databases. See for syntax details.
UNION queries cannot be used with .
EXCEPT and UNION have the same operation precedence and INTERSECT has a higher precedence, unless , in which case all three have the same precedence.
The ALL keyword causes duplicate rows to be preserved. The DISTINCT keyword (the default if the keyword is omitted) causes duplicate rows to be removed by the results.
UNION ALL and UNION DISTINCT can both be present in a query. In this case, UNION DISTINCT will override any UNION ALL to its left.
The server can in most cases execute UNION ALL without creating a temporary table (see ).
Individual SELECT statements can contain their own and clauses. In this case, the individual queries need to be wrapped between parentheses. However, this does not affect the order of the UNION, so they only are useful to limit the record read by one SELECT.
The UNION can have global and clauses, which affect the whole result set. If the columns retrieved by individual SELECT statements have an alias (AS), the ORDER BY must use that alias, not the real column names.
Specifying a query as does not work inside a UNION. If applied to the first SELECT, it is ignored. Applying to a later SELECT results in a syntax error:
Individual SELECT statements cannot be written or . If the last SELECT statement specifies INTO DUMPFILE or INTO OUTFILE, the entire result of the UNION will be written. Placing the clause after any other SELECT will result in a syntax error.
If the result is a single row, can also be used.
Parentheses can be used to specify precedence.
Parentheses cannot be used to specify precedence.
UNION between tables having different column names:
Specifying the UNION global order and limiting total rows:
Adding a constant row:
Differing types:
Returning the results in order of each individual SELECT by use of a sort column:
Difference between UNION, and :
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SELECT ...
UNION [ALL | DISTINCT] SELECT ...
[UNION [ALL | DISTINCT] SELECT ...]
[ORDER BY [column [, column ...]]]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]ERROR 1234 (42000): Incorrect usage/placement of 'HIGH_PRIORITY'(SELECT e_name AS name, email FROM employees)
UNION
(SELECT c_name AS name, email FROM customers);(SELECT name, email FROM employees)
UNION
(SELECT name, email FROM customers)
ORDER BY name LIMIT 10;(SELECT 'John Doe' AS name, 'john.doe@example.net' AS email)
UNION
(SELECT name, email FROM customers);SELECT CAST('x' AS CHAR(1)) UNION SELECT REPEAT('y',4);
+----------------------+
| CAST('x' AS CHAR(1)) |
+----------------------+
| x |
| yyyy |
+----------------------+(SELECT 1 AS sort_column, e_name AS name, email FROM employees)
UNION
(SELECT 2, c_name AS name, email FROM customers) ORDER BY sort_column;CREATE TABLE seqs (i INT);
INSERT INTO seqs VALUES (1),(2),(2),(3),(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 UNION ALL SELECT i FROM seqs WHERE i>=3;
+------+
| i |
+------+
| 1 |
| 2 |
| 2 |
| 3 |
| 3 |
| 3 |
| 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 EXCEPT ALL SELECT i FROM seqs WHERE i>=3;
+------+
| i |
+------+
| 1 |
| 2 |
| 2 |
+------+
SELECT i FROM seqs WHERE i <= 3 INTERSECT SELECT i FROM seqs WHERE i>=3;
+------+
| i |
+------+
| 3 |
+------+
SELECT i FROM seqs WHERE i <= 3 INTERSECT ALL SELECT i FROM seqs WHERE i>=3;
+------+
| i |
+------+
| 3 |
| 3 |
+------+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 |
+------+