MySQL的子查询的WHERE子句

Question

我有一个MySQL查询这是这样的：

select 
    *, 
    (select meta_value 
     from nord_usermeta m 
     where meta_key = 'firm' and user_id = s.user_id 
     limit 1) 
     as firm, 
    (select meta_value f 
     rom nord_usermeta m 
     where meta_key = 'first_name' and user_id = s.user_id 
     limit 1) 
    as first_name, 
    (select meta_value 
     from nord_usermeta m 
     where meta_key = 'last_name' and user_id = s.user_id 
     limit 1) 
    as last_name  
    from nord_submissions s 
    order by created_at desc 

现在我需要将它缩小与where子句是这样的：

select 
    *, 
    (select meta_value 
     from nord_usermeta m 
     where meta_key = 'firm' and user_id = s.user_id 
     limit 1) 
     as firm, 
    (select meta_value 
     from nord_usermeta m 
     where meta_key = 'first_name' and user_id = s.user_id 
     limit 1) 
    as first_name, 
    (select meta_value 
     from nord_usermeta m 
     where meta_key = 'last_name' and user_id = s.user_id 
     limit 1) 
    as last_name 

    from nord_submissions s 
    where firm like '%DG%' 
    order by created_at desc 

的问题显然是在我使用子查询的方式，但我无法找到一种方法在where子句中引用它。
请帮忙。

Answer 1

为什么要这么久......尝试自连接（连接查询相同的表）..见下文（未测试）

SELECT ns.*, 
     um1.meta_value AS firmName, 
     um2.meta_value AS firstName, 
     um3.meta_value AS lastName 
FROM nord_submission ns 
INNER JOIN nord_usermeta um1 USING(id) AND meta_key = 'firm' 
INNER JOIN nord_usermeta um2 USING(id) AND meta_key = 'first_name' 
INNER JOIN nord_usermeta um3 USING(id) AND meta_key = 'last_name' 
WHERE um1.meta_value LIKE '%DG%' 
ORDER BY ns.created_at 

注：如果两个表具有不同的列名，由其中U refrence对方，那么你可以在

Answer 2

与ns.user_id = um1.user_id等取代USING(id)如果你要使用的密钥，而不是列，你必须让应用程序把它清除出来。使用这么多的子查询，您会看到性能受到影响。

SELECT * 
FROM nord_submissions 
INNER JOIN nord_usermeta 
USING (user_id) 
WHERE (meta_key='last_name' or meta_key='first_name' or (meta_key='firm' and meta_value LIKE '%DG%')) 
ORDER BY created_at desc