[英]remove repeated rows while self join in sql
我正在尝试根据同一表上的连接从行中删除重复值,但无法删除 table1 中映射到 table2 中同一列的一列中的一个值。
表:注意:表中不限于只有一个日期,可以有多个带有多个sid的日期
date | sid | comp | disc
-----------------------
23 june | 1 | az | 20
23 june | 1 | ph | 22
23 june | 1 | mg | 10
23 june | 2 | mg | 8
23 june | 3 | ph | 15
23 june | 3 | az | 11
------------------------
自我加入
select t1.*, t2.comp as comp1, t2.disc as disc1
from table as t1
left join table as t2 on t1.date = t2.date and t1.sid = t2.sid and t1.comp <> t2.comp
Output from above query:
date | sid | comp | disc | comp1 | disc1
-------------------------------------------
23 june | 1 | az | 20 | ph | 22
23 june | 1 | az | 20 | mg | 10
23 june | 1 | ph | 22 | az | 20
23 june | 1 | ph | 20 | mg | 10
23 june | 1 | mg | 10 | mg | 10
23 june | 2 | mg | 10 | null | null
23 june | 3 | ph | 10 | az | 11
23 june | 3 | az | 11 | ph | 10
预期结果:(这里我试图获取 comp 和 comp1 的组合,其中对于每个 sid 和日期,不同的 comp 值仅映射为 mg 并且如果 sid 只有 mg 或非 mg 值,则 comp1 中的 null)注意:没有重复的行当 comp 映射到 comp1
date | sid | comp | disc | comp1 | disc1
-------------------------------------------
23 june | 1 | az | 20 | mg | 10
23 june | 1 | ph | 20 | mg | 10
23 june | 2 | mg | 10 | null | null
23 june | 3 | ph | 10 | null | null
23 june | 3 | az | 11 | null | null
WITH cte AS (
SELECT t1.*, t2.comp as comp1, t2.disc as disc1, SUM(1) OVER(PARTITION BY date,sid,comp) AS cnt
FROM `table` t1
LEFT JOIN `table` t2 ON t1.date = t2.date AND t1.sid = t2.sid AND t1.comp <> t2.comp
)
SELECT
date, sid, comp, disc,
CASE WHEN comp1 <> 'mg' THEN NULL ELSE comp1 END AS comp1,
CASE WHEN comp1 <> 'mg' THEN NULL ELSE disc1 END AS disc1
FROM cte
WHERE
(CASE WHEN comp <> 'mg' OR comp1 IS NULL THEN cnt END) = 1
OR
(CASE WHEN comp <> 'mg' AND comp1 = 'mg' THEN cnt END) >= 2
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