mysql筛选条件，求高手

Posted 2023-05-11

如图，该表部分数据

我要进行一个筛选。
1、比如我要取得标签为92的相册id，则得到结果的相册id有78，115，116
2、现在我又添加一个筛选条件，即在上一个筛选条件上增加取得标签为96这条件，那么取出的相册id有115和116，78就被排除了

这如何操作才好？似乎很麻烦啊，能否给个思路。
我目前想的是在上一次查询结果中再查询，但这怎么做到？或者有何其他更好的方法？

1)$sql="select infoid from tab where tagid in (92,96)";
2)$sql="select group_concat(infoid),tagid from tab where tagid in (92,96) group by tagid"; 参考技术A $的SQL？=“选择*从房子里house_price>'$ cdayprice'和定位='东城区' 参考技术B 逻辑似乎不太对吧，条件都是标签id，怎么分两次查询呢追问

不是光写成一条sql语句，估计写成一条是查不出来的。
我通过第一次筛选设定一个标签id，查询出来之后，我还要通过php语言组织下一个条件，再进行查询

MySQL数据库，内连接外连接中做条件筛选和WHERE中条件筛选的区别

最近写数据库SQL做连接、条件筛选数据操作时发现了一个问题，就是两张表在做等值连接、或者外连接时用AND对连接表数据进行筛选和最后用WHERE对结果集数据表进行筛选得到的查询结果是有区别的。

先来个简单例子看下，在对结果进行具体分析。

1.外连接

ON后用AND对连接表数据进行筛选

WITH table_1 AS(
    SELECT 'a1' AS id_1, 'b1' AS id_2, 'name_1' AS name_1
    UNION ALL
    SELECT 'a2' AS id_1, 'b2' AS id_2, 'name_2' AS name_1
    UNION ALL
    SELECT 'a3' AS id_1, 'b3' AS id_2, 'name_3' AS name_1
    UNION ALL
    SELECT 'a4' AS id_1, 'b1' AS id_2, 'name_4' AS name_1
),
table_2 AS(
    SELECT 'b1' AS id_2, 'aa' AS name_2
    UNION ALL
    SELECT 'b2' AS id_2, 'bb' AS name_2
)

SELECT
    *
FROM
    table_1
LEFT OUTER JOIN table_2
ON table_1.id_2 = table_2.id_2
AND table_2.name_2 = 'aa'
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结果

修改成WHERE对结果数据集筛选

WITH table_1 AS(
    SELECT 'a1' AS id_1, 'b1' AS id_2, 'name_1' AS name_1
    UNION ALL
    SELECT 'a2' AS id_1, 'b2' AS id_2, 'name_2' AS name_1
    UNION ALL
    SELECT 'a3' AS id_1, 'b3' AS id_2, 'name_3' AS name_1
    UNION ALL
    SELECT 'a4' AS id_1, 'b1' AS id_2, 'name_4' AS name_1
),
table_2 AS(
    SELECT 'b1' AS id_2, 'aa' AS name_2
    UNION ALL
    SELECT 'b2' AS id_2, 'bb' AS name_2
)

SELECT
    *
FROM
    table_1
LEFT OUTER JOIN table_2
ON table_1.id_2 = table_2.id_2
WHERE table_2.name_2 = 'aa'
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结果

2.等值连接

ON后用AND对连接表数据进行筛选

WITH table_1 AS(
    SELECT 'a1' AS id_1, 'b1' AS id_2, 'name_1' AS name_1
    UNION ALL
    SELECT 'a2' AS id_1, 'b2' AS id_2, 'name_2' AS name_1
    UNION ALL
    SELECT 'a3' AS id_1, 'b3' AS id_2, 'name_3' AS name_1
    UNION ALL
    SELECT 'a4' AS id_1, 'b1' AS id_2, 'name_4' AS name_1
),
table_2 AS(
    SELECT 'b1' AS id_2, 'aa' AS name_2
    UNION ALL
    SELECT 'b2' AS id_2, 'bb' AS name_2
)

SELECT
    *
FROM
    table_1
INNER JOIN table_2
ON table_1.id_2 = table_2.id_2
AND table_2.name_2 = 'aa'
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结果

修改成WHERE对结果数据集筛选

WITH table_1 AS(
    SELECT 'a1' AS id_1, 'b1' AS id_2, 'name_1' AS name_1
    UNION ALL
    SELECT 'a2' AS id_1, 'b2' AS id_2, 'name_2' AS name_1
    UNION ALL
    SELECT 'a3' AS id_1, 'b3' AS id_2, 'name_3' AS name_1
    UNION ALL
    SELECT 'a4' AS id_1, 'b1' AS id_2, 'name_4' AS name_1
),
table_2 AS(
    SELECT 'b1' AS id_2, 'aa' AS name_2
    UNION ALL
    SELECT 'b2' AS id_2, 'bb' AS name_2
)

SELECT
    *
FROM
    table_1
INNER JOIN table_2
ON table_1.id_2 = table_2.id_2
WHERE table_2.name_2 = 'aa'
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结果

原理：在等值连接、外连接ON后用AND做条件筛选数据时，是先对连接表的数据进行条件筛选，筛选后和被连接表进行相应连接，而WHERE是对结果集进行筛选，先连接后筛选数据。