曖昧的Mysql列

Question

我有這個疑問

SELECT t.employee_id, t.timeinhour,t.timeouthour, 
SEC_TO_TIME(SUM(TIME_TO_SEC(TIMEDIFF(t.timeouthour, t.timeinhour)))) 
AS Duration FROM timesheets t 
INNER JOIN employeetimesheets et 
ON t.employee_id=et.employee_id 
WHERE employee_id='6748372' 
AND timeinyear='2017' 
AND timeinmonth='March' 
AND isWeekNumber='1' 

它給了我這個錯誤

1052 - 列在where子句是曖昧

我 'EMPLOYEE_ID'看了here和here但我沒有使用all (*)所以我不明白爲什麼？

Answer 1

您需要where節定義表的別名，像這樣

SELECT t.employee_id, t.timeinhour,t.timeouthour, 
SEC_TO_TIME(SUM(TIME_TO_SEC(TIMEDIFF(t.timeouthour, t.timeinhour)))) 
AS Duration FROM timesheets t 
INNER JOIN employeetimesheets et 
ON t.employee_id=et.employee_id 
WHERE t.employee_id='6748372' 
AND t.timeinyear='2017' 
AND t.timeinmonth='March' 
AND t.isWeekNumber='1' 

如果從表employeetimesheets列設置et別名

Answer 2

要從中選擇表的產品包括兩個同名的列，這裏明顯：

ON t.employee_id=et.employee_id 

兩個timesheets和employeetimesheets有列。由於JOIN子句將確保產品中的這兩列始終具有相同的值，因此您指定的可能無關緊要。任何一個會做的工作：

WHERE t.employee_id='6748372' 

雖然你可能要運行在既有DESCRIBE，看看是否有在性能上有什麼區別。

Answer 3

您必須指定您指的是哪張表。試試這個，並注意更新WHERE行：

SELECT t.employee_id, t.timeinhour,t.timeouthour, 
SEC_TO_TIME(SUM(TIME_TO_SEC(TIMEDIFF(t.timeouthour, t.timeinhour)))) 
AS Duration FROM timesheets t 
INNER JOIN employeetimesheets et 
ON t.employee_id=et.employee_id 
WHERE t.employee_id='6748372' 
AND timeinyear='2017' 
AND timeinmonth='March' 
AND isWeekNumber='1'