MySQL查询是否加入

Question

SELECT * FROM bn_garant_tpl 
JOIN bn_garant_val
WHERE bn_garant_tpl.what_tpl IN (1, 2)
AND bn_garant_tpl.id_tpl = bn_garant_val.id_garant_tpl
ORDER BY ords ASC

如何获取what_tpl = 1的行？

问题是下一个：在表bn_garant_val中不存在行如果what_tpl = 1 。仅适用于 if what_tpl = 2 。

如果ID匹配

，则返回此查询

AND bn_garant_tpl.id_tpl = bn_garant_val.id_garant_tpl

但是，结果必须是：如果 what_tpl = 1 也是

Answer 1

如果您需要bn_garant_tpl中的记录，即使bn_garant_val中没有此类记录，请使用LEFT JOIN：

SELECT * FROM bn_garant_tpl 
LEFT JOIN bn_garant_val ON bn_garant_tpl.id_tpl = bn_garant_val.id_garant_tpl
WHERE bn_garant_tpl.what_tpl IN (1, 2)
ORDER BY ords ASC