如何在 MySQL 的 WHERE 子句中使用计算字段？

Posted 2023-05-09

【中文标题】如何在 MySQL 的 WHERE 子句中使用计算字段？

【英文标题】：How can I use calculated fields in a WHERE clause with MySQL?

【发布时间】：2015-03-05 09:06:11

【问题描述】：

我有这样的查询：

SELECT client_id,name, last_name, email,  date_arrival,
  DATE_SUB(now(),INTERVAL 6 DAY) as date6before  FROM clients WHERE agent_id = 4 
    and  date_arrival > date6before

我怎样才能做到这一点？

【参考方案1】：

你可以再次计算where中的值：

SELECT client_id,name, last_name, email,  date_arrival,
  DATE_SUB(now(),INTERVAL 6 DAY) as date6before  FROM clients WHERE agent_id = 4 
    and  date_arrival > DATE_SUB(now(),INTERVAL 6 DAY) 

或使用having 子句

SELECT client_id,name, last_name, email,  date_arrival,
  DATE_SUB(now(),INTERVAL 6 DAY) as date6before  FROM clients WHERE agent_id = 4 
    having  date_arrival > date6before   

【参考方案2】：

试试这个：

SELECT temp.* FROM (SELECT client_id,name, last_name, email,  date_arrival, DATE_SUB(now(),INTERVAL 6 DAY) as date6before  FROM clients WHERE agent_id = 4 ) as temp WHERE temp.date_arrival > date6before