Question

我写了下面的SQL语句并得到结果，当我添加where name = statement时它不识别'name'

SELECT CONCAT( `Surname` , ' ', `firstname` ) AS NAME 
FROM Prospects
UNION 
SELECT CONCAT( `last_name` , ' ', `first_name` ) AS NAME 
FROM customer
ORDER BY name;

Answer 1

有两种选择。

为每个SELECT添加WHERE子句。在同一查询的WHERE子句中，由分配的别名引用SELECT列表中的表达式结果是不可能的。要在WHERE子句中指定谓词，您需要重复表达式：

 SELECT CONCAT(p.surname,' ',p.firstname) AS NAME 
   FROM Prospects p
  WHERE CONCAT(p.surname,' ',p.firstname)  = ?
  UNION 
 SELECT CONCAT(c.last_name,' ',c.first_name)
   FROM customer c
  WHERE CONCAT(c.last_name,' ',c.first_name)  = ?
  ORDER BY 1

MySQL扩展了SQL标准，并允许HAVING子句引用不在GROUP BY中的非聚合表达式

 SELECT CONCAT(p.Surname,' ',p.firstname) AS NAME 
   FROM Prospects p
 HAVING NAME  = ?
  UNION 
 SELECT CONCAT(c.last_name,' ',c.first_name) AS NAME 
   FROM customer c
 HAVING NAME  = ?
  ORDER BY 1

要在WHERE子句中按名称引用别名，可以使用内联视图。但请注意，可能存在显着的性能损失，因为谓词不被推入内联视图。这意味着MySQL将实现视图查询中的所有行作为派生表，然后外部查询将针对派生表运行。不要这样做，特别是对于大桌子：

SELECT v.name
  FROM ( SELECT CONCAT(p.Surname,' ',p.firstname) AS NAME 
           FROM Prospects p
          UNION
         SELECT CONCAT(c.last_name,' ',c.first_name)
           FROM customer c
       ) v
 WHERE v.name  = ? 
 ORDER BY 1

Answer 2

SELECT 
    CONCAT( Surname , ' ', firstname ) AS NAME FROM Prospects 
UNION 
SELECT 
    CONCAT( last_name , ' ', first_name ) AS NAME FROM customer 
WHERE 
    CONCAT( Surname , ' ', firstname ) = <statement> or
    CONCAT( last_name, ' ', firstname ) = <statement> 
ORDER BY name;

来自concat / union脚本的where语句

2 个答案: