clear markdown compare help best fiddles feedback
clear markdown feedback
By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0. 3601504 fiddles created (47950 in the last week).

select version();
version()
5.6.47
 hidden batch(es)


CREATE TABLE x1 (y INTEGER NOT NULL);
 hidden batch(es)


CREATE TABLE a1 (b INTEGER NOT NULL, INDEX(b));
 hidden batch(es)


INSERT INTO x1 VALUES (1), (1), (2), (2), (3), (3), (4), (5);
 hidden batch(es)


INSERT INTO a1 VALUES (3), (3), (4), (5), (6), (6), (7), (7), (8);
 hidden batch(es)


-- SELECT * FROM x1; SELECT * FROM a1;
 hidden batch(es)


-- Query 1 - same result as for Query 2 - DISTINCT is redundant SELECT y FROM x1 UNION SELECT b FROM a1;
y
1
2
3
4
5
6
7
8
 hidden batch(es)


-- Query 2 - same result as for Query 1 - DISTINCT is redundant SELECT y FROM x1 UNION SELECT DISTINCT b FROM a1;
y
1
2
3
4
5
6
7
8
 hidden batch(es)


-- Query 3 - UNION ALL - all dupes are included SELECT y FROM x1 UNION ALL SELECT b FROM a1;
y
1
1
2
2
3
3
4
5
3
3
4
5
6
6
7
7
8
 hidden batch(es)


SELECT y FROM x1 UNION DISTINCT SELECT b FROM a1;
y
1
2
3
4
5
6
7
8
 hidden batch(es)