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Mysql union联合查询

super
2021-04-15 19:10
views 348

1.UNION 用于合并两个或多个 SELECT 语句的结果集,并消去表中任何重复行。
2.UNION 内部的 SELECT 语句必须拥有相同数量的列,列也必须拥有相似的数据类型,每条 SELECT 语句中的列的顺序必须相同.
3.UNION ALL允许有重复的行

 

SELECT column_name FROM table1 

UNION 

SELECT column_name FROM table2 

 

UNION ALL不消除重复行

 

SELECT column_name FROM table1

UNION ALL

SELECT column_name FROM table2

 

重复

 

(select * from talbe order by id) UNION ALL (select * from talbe order by id);

 

不重复

 

(select * from talbe order by id) UNION (select * from talbe order by id);

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