就是把多个结果集合并成一个结果集
比如说select userid ,name from user where sex ='男' and age <18;select userid ,name from user where sex ='女' and age <18;select userid ,name from user where sex ='女' and age >60;
这些含有相同列结果的sql可以合并成一个大的结果集
select userid ,name from user where sex ='男' and age <18 union
select userid ,name from user where sex ='女' and age <18 union
select userid ,name from user where sex ='女' and age <18;你执行这个查询就得到满足上面三个条件的并集
比如说select userid ,name from user where sex ='男' and age <18;select userid ,name from user where sex ='女' and age <18;select userid ,name from user where sex ='女' and age >60;
这些含有相同列结果的sql可以合并成一个大的结果集
select userid ,name from user where sex ='男' and age <18 union
select userid ,name from user where sex ='女' and age <18 union
select userid ,name from user where sex ='女' and age <18;你执行这个查询就得到满足上面三个条件的并集
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