mysql左连接查询结果不准确

Posted 2021-04-04 無玑小姐

现有四张表

表(1)res_resource_catalog

表(2)res_catalog_classify

表(3)res_resource_classify

表(4)res_resource_mount

其中,表3是表1和表2的中间表,表1的主键是表4的外键

现在要统计表2中某一类型的表1的当前用户创建的数据量,以及表1相关的表4的数据量

一开始的sql如下:

SELECT rcc.id, rcc.catalog_name, COUNT(DISTINCT rrc.id) AS resourceCatalogCount,COUNT(DISTINCT rrm.id) AS resourceCount FROM
        (SELECT * FROM res_catalog_classify WHERE catalog_type = #{catalogType} AND parent_id != \'0\' AND is_publish = 1) rcc
        LEFT JOIN res_resource_classify rrc ON rcc.id = rrc.classify_id
        LEFT JOIN res_resource_catalog rrc1 ON rrc.resource_id = rrc1.id
        LEFT JOIN res_resource_mount rrm ON rrc.resource_id = rrm.resource_id
        <where>
            <if test="createUser != null and createUser != \'\'">
                AND rrc1.create_user = #{createUser}
            </if>
            AND rrc1.is_publish = 1
        </where>
        GROUP BY rcc.id

结果查询不准确,当createUser没有在表1中创建数据时,查询结果为null,实际应该是表2数据有,但是结果中的resourceCatalogCount为0,经改正后的sql如下:

SELECT rcc.id, rcc.catalog_name, COUNT(DISTINCT rrc1.id) AS resourceCatalogCount,COUNT(DISTINCT rrm.id) AS resourceCount FROM
        (SELECT * FROM res_catalog_classify WHERE catalog_type = #{catalogType} AND parent_id != \'0\' AND is_publish = 1) rcc
        LEFT JOIN res_resource_classify rrc ON rcc.id = rrc.classify_id
        LEFT JOIN (
        SELECT * FROM res_resource_catalog 
        <where>
            <if test="createUser != null and createUser != \'\'">
                AND rrc1.create_user = #{createUser}
            </if>
            AND rrc1.is_publish = 1
        </where>
        ) rrc1 ON rrc.resource_id = rrc1.id
        LEFT JOIN res_resource_mount rrm ON rrc.resource_id = rrm.resource_id
        GROUP BY rcc.id