php - 显示 9 个结果的 mysql 查询

Question

我有一个问题。

我正在运行以下查询。我的数据库中只有一条记录，但我得到了 9 个结果。

SELECT c.id, c.rk 
FROM cv AS c, employee AS e , cvCat AS cv_cat 
WHERE c.status=1 
    AND c.empIDFK = e.id 
    AND cv_cat.categoryFK IN ( 17,18,19,38,39,40,41,44,45,46 ) 
    AND cv_cat.cvFK = c.id

如果有人对此查询有任何问题，请告诉我。为什么我得到 9 个结果而不是 1 个结果。

这个查询应该只显示一条记录，但它显示了 9 个结果。

Answer 1

当你做的时候

FROM cv AS c, employee AS e , cvCat AS cv_cat

您正在对三个表进行隐式连接。如果你想获得不同的记录，你可以在你的选择之后添加 DISTINCT:

SELECT DISTINCT c.id, c.rk 
FROM cv AS c, employee AS e , cvCat AS cv_cat 
WHERE c.status=1 
    AND c.empIDFK = e.id 
    AND cv_cat.categoryFK IN ( 17,18,19,38,39,40,41,44,45,46 ) 
    AND cv_cat.cvFK = c.id