UNION-和-UNION-ALL的区别，一个例子就看明白

tech mysql sql

发布时间 : 2020-09-01 00:00

字数:125 阅读 :

【UNION ALL】
【UNION】

【UNION ALL】

select a,b,sum(sm) AS s1, SUM(qm) AS s2 from   
(  
 select 'a' AS a, 'b' AS b, 2 AS sm, 200 AS qm   
UNION ALL  
 select 'a' AS a, 'b' AS b, 2 AS sm, 200 AS qm  
)r  
group by a,b

ab4400

【UNION】

select a,b,sum(sm) AS s1, SUM(qm) AS s2 from   
(  
 select 'a' AS a, 'b' AS b, 2 AS sm, 200 AS qm   
UNION   
 select 'a' AS a, 'b' AS b, 2 AS sm, 200 AS qm  
)r  
group by a,b

ab2200

总结：UNION ALL全部列出，UNION会去掉重复的

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