UNION-MINUS-INTERSECT-UNIONALL

SQL> select * from a;

A
----------
1
2
3

SQL> select * from b;

B
----------
1
4
=========================UNION；列出所有，但重复项只列出一次=========================
SQL> select * from a union select * from b;

A
----------
1
2
3
4
=========================差集；列出不重复的项========================================
SQL> select * from a minus select * from b;

A
----------
2
3
=========================交集；列出重复的项========================================
SQL> select * from a intersect select * from b;

A
----------
1
========================全并集；列出所有的项======================================
SQL> select * from a union all select * from b;

A
----------
1
2
3
1
4

[@more@]

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