MySQL的派生最大功能列添加條件

Question

我有以下的SQL不適用於where條件。

SELECT t.PROJID,sum(t.UNITS) AS totalunits, sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` 
left join projects on projects.PROJID = t.PROJID 
where lastupdated LIKE '%2014-06-11%' 
GROUP BY t.PROJID 

Answer 1

您不應在日期使用like。正確的解決方案是簡單地截斷日期並進行比較。但是，您需要使用數據的字段：

SELECT t.PROJID, sum(t.UNITS) AS totalunits, 
     sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` left join 
    projects on projects.PROJID = t.PROJID 
where date(t.date) = date('2014-06-11') 
GROUP BY t.PROJID; 

或者，如果你有lastupdated索引，使用範圍允許使用索引：

SELECT t.PROJID, sum(t.UNITS) AS totalunits, 
     sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` left join 
    projects on projects.PROJID = t.PROJID 
where t.date >= date('2014-06-11') and t.date < date('2014-06-12') 
GROUP BY t.PROJID; 

你真的有可能想要使用having，這是使用列別名而不是基列建議的。在這種情況下：

SELECT t.PROJID, sum(t.UNITS) AS totalunits, 
     sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` left join 
    projects on projects.PROJID = t.PROJID 
GROUP BY t.PROJID 
HAVING date(lastupdated) = date('2014-06-11'); 

Answer 2

像永遠不能用於日期字段。 如果您將類型更改爲vachar，則可以使用