Question

需要检查where案例，如果找不到where type='P'则会记录type='C'

这是表格

paper_id  | product_id  | type
    1          1           P
    2          1           P
    3          1           C
    4          1           C
    5          2           C
    6          2           C

有product_id 1和2，需要获取具有type='P'的记录，但那些记录没有type='P'的产品会从记录中获取type='C'

查询后需要此结果

paper_id  | product_id  | type
    1          1           P
    2          1           P
    5          2           C
    6          2           C

我试试

select * from table where CASE WHEN type !='P' THEN type='C' ELSE type='P'END

但没有工作

Answer 1

select paper_id, product_id, type from your_tab
where type = 'P'
union all
select t1.paper_id, t1.product_id, t1.type from your_tab t1
where t1.type = 'C'
  and not exists (select 1 from your_tab t2 
                  where t2.product_id = t1.product_id and t2.type = 'P');

Answer 2

也许这会有所帮助

SELECT DISTINCT T.PRODUCT_ID, T.PAPER_ID, T.TYPE FROM YOUR_TABLE T WHERE (CASE WHEN T.TYPE = 'P' THEN 'TRUE' WHEN T.TYPE != 'P' THEN (CASE WHEN (SELECT COUNT(*) FROM YOUR_TABLE T2 WHERE T2.PRODUCT_ID = T.PRODUCT_ID AND T2.TYPE = 'P') = 0 THEN 'TRUE' ELSE 'FALSE' END) END) = 'TRUE'

如果没有在记录中找到，那么在mysql中获取其他情况

2 个答案: