mysql - SUBSTR 没有返回记录 (mysql)

Question

SELECT jour 
FROM reservations 
WHERE id_user = 57 AND SUBSTR(jour,10) = '2014_08_14' ORDER BY jour 

什么都不返回...

我在数据库中有一条符合条件的记录:

Answer 1

substr的第一个参数是开始的位置。因此，SUBSTR(jour,10) 返回 _AM，您会得到一个空结果集。相反，您应该使用树参数变体:

SELECT   jour
FROM     reservations 
WHERE    id_user = 57 AND 
         SUBSTR(jour, 1, 10) = '2014_08_14' -- Here
ORDER BY jour 

为了使您的查询更具可读性并确保不再重复此类错误，您可以使用以下变体:

SELECT   jour
FROM     reservations 
WHERE    id_user = 57 AND 
         SUBSTR(jour FROM 1 FOR 10) = '2014_08_14' -- Here
ORDER BY jour