Question

以下查询对我来说绝对正常：

SELECT * From Customers
WHERE Customers.ContactName = (SELECT FirstName
                               FROM Employees as E, orders as O
                               WHERE <condition>
                               LIMIT 1);

但是，如果我使用LIKE而不是=来与子查询的结果进行比较，那么我没有得到任何结果。如何在上述查询中使用LIKE '%%'？

Answer 1

首先，此查询应该无法正常工作：

SELECT *
From Customers
WHERE Customers.ContactName = (SELECT FirstName
                               from Employees as E, orders as O
                               WHERE LIMIT 1);

因为WHERE LIMIT 1不是正确的SQL。而且，您应该学会使用正确的join语法。据推测，你打算：

SELECT c.*
From Customers c
WHERE c.ContactName = (SELECT FirstName
                       FROM Employees as E JOIN
                            Orders as O
                            ON . . .
                       LIMIT 1
                      );

您可以想象在子查询中添加LIKE而不是=和'％'：

WHERE c.ContactName LIKE (SELECT CONCAT('%', FirstName, '%') . . .

但我会用EXISTS来写这个：

SELECT c.*
From Customers c
WHERE EXISTS (SELECT 1
              FROM Employees as E JOIN
                   Orders as O
                   ON . . .
              WHERE c.ContactName LIKE CONCAT('%', FirstName, '%')
             );

这与您的查询完全不同。它做了更合理的事情。它将确定子查询中是否存在任何匹配，而不是比较子查询中的一个随机名称。对于查询来说，这似乎是一个更合理的意图。

Answer 2

我想这对你有用，不是吗？

SELECT * From Customers
WHERE Customers.ContactName LIKE '%' + (
        SELECT FirstName from Employees as E, orders as O
        WHERE <condition>
        LIMIT 1
    ) + '%';

Answer 3

使用您的方法，您需要使用＆＃39;％＆＃39;包装FirstName字段。任意一方将通配符放在您选择的值中。

所以，像

SELECT * From Customers 
 WHERE Customers.ContactName LIKE (SELECT '%' + FirstName + '%'
                                    from Employees as E
                                   inner join, orders as O on...
                                   WHERE <condition>
                                   LIMIT 1);

对我而言，就像你最好加入你的桌子一样。也许这会更好

SELECT c.* 
  FROM Customers c
 INNER JOIN Employees e on c.ContactName like '%' + e.FirstName + '%'
 WHERE <condition>

Answer 4

以下查询是 MSSQL 语句，而不是LIKE，我使用 CHARINSDEX 。尝试MySQL中的相关功能（检查INSTR功能）而不是CHARINDEX。

SELECT
    *
FROM
    Customers
WHERE
    CHARINDEX(( SELECT  TOP 1 FirstName
                FROM    Employees as E, orders as O
                WHERE   <condition>
                ), Customers.ContactName, 1
             ) > 0;

我不确定，但您可以在MySQL中尝试以下内容。

SELECT
    *
FROM
    Customers
WHERE
    INSTR(Customers.ContactName,
          ( SELECT  FirstName
            FROM    Employees as E, orders as O
            WHERE   <condition>
            LIMIT 1)) > 0;

Answer 5

为什么不使用简单的INNER JOIN：

SELECT Customers.*
FROM Customers
INNER JOIN Employees ON Customers.ContactName LIKE CONCAT('%', Employees.FirstName,'%')
WHERE Employees.Foo = 'Bar'

注意：+是加法运算符，不能用于连接字符串。

Answer 6

SQL Server

这将返回特定关键字

select * 
from Customers
where Customers.ContactName like (select top 1 FirstName from Employees )

如果关键字存在，则会返回

select * 
from Customers
where Customers.ContactName like '%' + (select top 1 FirstName from Employees) + '%'

Answer 7

我建议：

SELECT * From Customers as a
INNER JOIN (SELECT '%'+FirstName+'%' as FirstName from Employees as E, orders as O
                               WHERE <condition>
                               LIMIT 1) as b
ON a.ContactName LIKE b.Firstname;

Answer 8

如果您拥有员工表的外键，则无需使用 LIKE 。但是，如果您想使用它，可以尝试以下

select * 
from customers a, employees b 
where (contions on employees) 
  and customers.contactname like '%'||b.firstname||'%';

使用'LIKE'和SQL子查询的结果

8 个答案: