Question

我有4个不同的表，为用户存储不同的事务，我想为某些特定用户联合所有事务。但问题是，所有这4个表都有大量数据，因此当我尝试UNION所有这些并与用户一起加入时，计算需要数小时。我正在做的是：

SELECT blablabla
FROM transactions1 t1
JOIN users ON (users.id = t1.user_id AND user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey')
UNION
SELECT blablabla
FROM transactions2 t2
JOIN users ON (users.id = t2.user_id AND user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey')
UNION
SELECT blablabla
FROM transactions3 t3
JOIN users ON (users.id = t3.user_id AND user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey')
UNION
SELECT blablabla
FROM transactions4 t4
JOIN users ON (users.id = t4.user_id AND user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey')
ORDER BY date DESC

问题是，我正在跑步 JOIN users ON (users.id = t1.user_id AND user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey')此过滤器通过将每个事务表与用户连接4次。

为了获得最佳实践并提高查询效率，我该如何改进查询？

谢谢！

Answer 1

使用Common Table Expression或临时表格从用户中选择“ user.state = 1 AND user.friends＆gt; 1 AND user.loc ='Turkey'”

然后在你的联盟中使用该结果。

Answer 2

您可以尝试这样的事情：

SELECT blablabla
FROM transactions1 t1, transactions2 t2,transactions3 t3,transactions4 t4
JOIN users ON (users.id = t1.user_id OR users.id = t2.user_id OR users.id = t3.user_id 
OR users.id = t4.user_id AND user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey');

Answer 3

检查所有具有条件的字段是否为INDEXED。（t.user_id，用户：州，朋友，loc）也尝试使用它：

select blablabla from
(
  select * from user where user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey'
) U1
join transactions1 t1 on (U1.Id=t1.User_id)

UNION ALL

select blablabla from
(
  select * from user where user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey'
) U1
join transactions1 t2 on (U1.Id=t2.User_id)

UNION ALL

select blablabla from
(
  select * from user where user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey'
) U1
join transactions1 t3 on (U1.Id=t3.User_id)

UNION ALL

select blablabla from
(
  select * from user where user.state = 1 AND user.friends > 1 AND user.loc = 'Turkey'
) U1
join transactions1 t4 on (U1.Id=t4.User_id)

SQL - 在union中多次加入一个子查询

3 个答案: