Question

我有以下查询加入一堆表。

我想从INDUSTRY表中获取unity_industry_id = 1的每条记录，无论它是否与其他表匹配。我相信这需要通过LEFT JOIN来完成吗？

SELECT attr.industry_id        AS option_id,
       attr.industry           AS option_name,
       uj.ft_job_industry_id,
       Avg(CASE
             WHEN s.salary > 0 THEN s.salary
           END)                AS average,
       Count(CASE
               WHEN s.salary > 0 THEN attr.industry
             END)              AS count_non_zero,
       Count(attr.industry_id) AS count_total
FROM   industry attr,
       user_job_ft_job uj,
       salary_ft_job s,
       user_job_ft_job ut,
       [user] u,
       user_education_mba_school mba
WHERE  u.user_id = uj.user_id
       AND u.user_id = ut.user_id
       AND u.user_id = mba.user_id
       AND uj.ft_job_industry_id = attr.industry_id
       AND uj.user_job_ft_job_id = s.user_job_id
       AND u.include_in_student_site_results = 1
       AND u.site_instance_id IN ( 1 )
       AND uj.job_type_id = 1
       AND attr.consolidated_industry_id = 1
       AND mba.mba_graduation_year_id NOT IN ( 8, 9 )
       AND uj.admin_approved = 1
GROUP  BY attr.industry_id,
          attr.industry,
          uj.ft_job_industry_id

这只返回一行，但行业表中有8个匹配，其中consolidated_industry_id = 1.

---编辑：这里真正的问题是，如何将LEFT JOIN与常规连接结合起来？

Answer 1

对可能错过相应记录的表使用left join。将每个表的条件放在on的{{1}}子句中，而不是join中，因为这实际上会使它们成为内连接。类似的东西：

where

如果您知道任何表格总是有相应的记录，那么只需使用select attr.industry_id AS option_id, attr.industry AS option_name, uj.ft_job_industry_id, AVG(CASE WHEN s.salary > 0 THEN s.salary END) AS average, COUNT(CASE WHEN s.salary > 0 THEN attr.industry END) as count_non_zero, COUNT(attr.industry_id) as count_total from industry attr left join user_job_ft_job uj on uj.ft_job_industry_id = attr.industry_id and uj.job_type_id = 1 and uj.admin_approved = 1 left join salary_ft_job s on uj.user_job_ft_job_id = s.user_job_id left join [user] u on u.user_id = uj.user_id and u.include_in_student_site_results = 1 and u.site_instance_id IN (1) left join user_job_ft_job ut on u.user_id = ut.user_id left join user_education_mba_school mba on u.user_id = mba.user_id and mba.mba_graduation_year_id not in (8, 9) where attr.consolidated_industry_id = 1 group by attr.industry_id, attr.industry, uj.ft_job_industry_id即可。

SQL LEFT JOIN与常规连接相结合

1 个答案: