如何获取left join后，符合条件的有多少条

2018-05-08 05:40:09 982 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

【后端百科】mysql的join，left join，right join，full join分别是什么意思在MySQL数据库中，JOIN操作是一种强大的工具，用于将两个或多个表中的数据进行组合，以满足复杂的查询需求。本文将详细介绍MySQL中的四种主要JOIN类型：INNER JOIN、LEFT JOIN、RIGHT JOIN和FULL OUTER JOIN（虽然MySQL不直接支持FULL OUTER JOIN，但可以通过其他方式实现类似效果），并对它们进行对比分析。MySQL提供了多种类型的JOIN操作，每种JOIN都有其特定的用途和语法。在实际应用中，应根据具体需求选择合适的JOIN类型。阅读详情

SELECT a.*,

      COUNT(*) AS 'population'

    FROM   `course_degree` a

      LEFT JOIN course_package cp ON cp.`courOrDegrCode` = a.`DEGR_CODE`

      LEFT JOIN (SELECT *

        FROM contract_course_package

        WHERE CONT_PACK_STAR >= '2018-05-08'

        GROUP BY pack_code,

          chil_code) ccp ON ccp.`PACK_CODE` = cp.`PACK_CODE`

      LEFT JOIN contract c ON c.`cont_code` = ccp.`CONT_CODE`

      LEFT JOIN (SELECT  *

        FROM `fund_income_print` GROUP BY cont_code) f ON f.cont_code = c.`cont_code`

      LEFT JOIN

        (SELECT a.*,

            cp.cont_code,

            cp.pers_code,

            cp.pers_name

          FROM course_arrange a

            LEFT JOIN (SELECT *

              FROM  `course_person`

              WHERE cont_code IS NOT NULL) cp ON cp.pare_id = a.`AUTO_ID`

            LEFT JOIN sys_office o ON o.id = a.`TRAI_CODE`

          WHERE cp.cont_code IS NOT NULL AND a.`ARRA_DATE` >= '2018-05-08'

            AND ( o.id = 1 OR o.parent_ids LIKE CONCAT('%,', 1, ',%')) GROUP BY cp.pers_code,

            a.COUR_DEGR) ca ON ca.`COUR_DEGR` = a.`DEGR_CODE`

      LEFT JOIN sys_office o ON o.id = f.trai_code

    WHERE a.`del_flag` = 0

      AND f.inco_code IS NOT NULL

      AND ( o.id = 1 OR o.parent_ids LIKE CONCAT('%,', 1, ',%'))

    GROUP BY a.`DEGR_CODE`