mysql - 不符合条件的sql联合

Question

我有这个查询，它是基于条件的多项选择的联合。 问题是“AND”部分仅应用于最后一个选择，但我想将其应用于整个选择(所有联合)

select * from
(select con.id_contact as  v,substr(concat(ifnull(con.firstname,''),ifnull(con.lastname,'')),1,4) as s0,   null as s1, null as s2 from contact con, fu_rec_group_link g
where con.id_contact = g.id_rec and id_group=125801) as tbl244295 where 1=1   UNION
select * from
(select con.id_contact as v,substr(concat(ifnull(con.firstname,''),ifnull(con.lastname,'')),1,4) as s0, null as s1, null as s2 from contact con, fu_rec_group_link g where
con.id_contact = g.id_rec and id_group=125803) as tbl244296 where 1=1 UNION
select * from
(select con.id_contact as  v,substr(concat(ifnull(con.firstname,''),ifnull(con.lastname,'')),1,4) as s0,  null as s1, null as s2 from contact con, fu_rec_group_link g where
con.id_contact = g.id_rec and id_group=126270) as tbl244297 where 1=1 AND v NOT IN
(select v from (select * from (select con.id_contact as v,substr(concat(ifnull(con.firstname,''),ifnull(con.lastname,'')),1,4) as s0, null as s1, null as s2 from contact con
where id_user=11944 and unregistered is not null) as tbl244299 where 1=1) as tblMinus ) 

Answer 1

正如@jarlh 所指出的那样，您的原始查询的解决方法是将联合包装在另一个选择中，并将最后一个 where 条件应用于该选择。此外，当您使用不带 all 的 union 时，您可以消除重复项，但这种方式可能代价高昂；最好指定 union all 并使用 distinct 或 group by 子句来消除重复行。

但是......看看你的查询，它似乎可以简化很多并减少到下面的查询，它应该呈现相同的结果但性能更好。

select distinct
    con.id_contact as v, 
    substr(concat(ifnull(con.firstname,''),ifnull(con.lastname,'')),1,4) as s0, 
    null as s1, 
    null as s2 
from contact con
join fu_rec_group_link g on con.id_contact = g.id_rec 
where id_group in (125801, 125803, 126270)
and con.id_contact not in (
    select con.id_contact as v
    from contact con
    where id_user=11944 and unregistered is not null
) 

由于既没有任何关于表格设计的信息，也没有任何数据来测试我的假设可能是完全错误的，如果是这样我会立即删除答案。