mysql - 带有 CONCAT 条件的 MySQL 选择

Question

我试图在我的脑海中编译这个..我有一个包含名字和姓氏字段的表，我有一个像“Bob Jones”或“Bob Michael Jones”这样的字符串等等。

问题是，例如，我的名字中有 Bob，姓氏中有 Michael Jones

所以我想

SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
  FROM users 
 WHERE firstlast = "Bob Michael Jones"

但它说未知列“firstlast”..有人可以帮忙吗？

Answer 1

您提供的别名用于查询的输出 - 它们在查询本身中不可用。

您可以重复表达式：

SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
FROM users
WHERE CONCAT(firstname, ' ', lastname) = "Bob Michael Jones"

或包装查询

SELECT * FROM (
  SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
  FROM users) base 
WHERE firstLast = "Bob Michael Jones"

Answer 2

尝试这个：

SELECT * 
  FROM  (
        SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
        FROM users 
    ) a
WHERE firstlast = "Bob Michael Jones"

Answer 3

SELECT needefield, CONCAT(firstname, ' ',lastname) as firstlast 
FROM users 
WHERE CONCAT(firstname, ' ', lastname) = "Bob Michael Jones"

Answer 4

使用 CONCAT_WS()。

SELECT CONCAT_WS(' ',firstname,lastname) as firstlast FROM users 
WHERE firstlast = "Bob Michael Jones";

第一个参数是其余参数的分隔符。

Answer 5

尝试：

SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
  FROM users 
WHERE CONCAT(firstname, ' ', lastname) = "Bob Michael Jones"

除非您将查询作为子选择进行，否则您的别名 firstlast 在查询的 where 子句中不可用。

Answer 6

除了重复CONCAT表达式或使用子查询之外，还有另一种方法。您可以使用HAVING识别列别名的子句。

SELECT 
  neededfield, CONCAT(firstname, ' ', lastname) AS firstlast 
FROM
  users 
HAVING firstlast = "Bob Michael Jones"

这是一个有效的SQL Fiddle。