如何解决SQL 根据另一个表查找缺少列的行
我有一个场景,我需要使用一个有效元素表来查找另一个表中缺少这些元素的记录,以便我可以反过来修补它们。这有点棘手,因为缺少的列数据在“嵌套”列(例如,它在另一列中具有重复条目)。我觉得某种 LEFT OUTER JOIN 可能在这里起作用,但我不能完全理解。 FWIW,我的基准是 Oracle 19c,但我最终也需要支持 Postgres 11+。问题总结为:
给定租户表:
租户 |
---|
1000 |
2000 |
3000 |
还有一个组表,其中每一天对应一个新的组id,每个组有一对多的租户,其中每个租户对应一个子组id:
日期 | 组 | 租户 | 子组 |
---|---|---|---|
2021-02-16 | G1 | 1000 | SG1 |
2021-02-16 | G1 | 2000 | SG2 |
2021-02-16 | G1 | 3000 | SG3 |
2021-02-17 | G2 | 1000 | SG4 |
2021-02-17 | G2 | 2000 | SG5 |
2021-02-18 | G3 | 2000 | SG6 |
2021-02-18 | G3 | 3000 | SG7 |
2021-02-19 | G4 | 1000 | SG8 |
查找缺少租户的组:
组 | 租户 |
---|---|
G2 | 3000 |
G3 | 1000 |
G4 | 2000 |
G4 | 3000 |
解决方法
WITH
tab1 AS
( SELECT TO_DATE('16.02.2021','DD.MM.YYYY') AS date_col,'G1' AS group_col,1000 AS tenant,'SG1' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('16.02.2021',2000 AS tenant,'SG2' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('16.02.2021',3000 AS tenant,'SG3' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('17.02.2021','G2' AS group_col,'SG4' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('17.02.2021','SG5' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('18.02.2021','G3' AS group_col,'SG6' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('18.02.2021','SG7' AS subgroup FROM DUAL
UNION ALL
SELECT TO_DATE('19.02.2021','G4' AS group_col,'SG8' AS subgroup FROM DUAL
),tab2 AS
( SELECT 1000 AS tenant FROM DUAL
UNION ALL
SELECT 2000 AS tenant FROM DUAL
UNION ALL
SELECT 3000 AS tenant FROM DUAL
)
SELECT *
FROM ( SELECT t1.group_col,t2.tenant
FROM ( SELECT DISTINCT group_col FROM tab1) t1
CROSS JOIN tab2 t2
) x
WHERE NOT EXISTS ( SELECT *
FROM tab1
WHERE tab1.group_col = x.group_col
AND tab1.tenant = x.tenant
)
ORDER BY group_col,tenant;
结果:
GR TENANT
-- ----------
G2 3000
G3 1000
G4 2000
G4 3000
该查询也适用于 Postgres(然后删除 FROM DUAL
,否则您将使其适应您的表格)。
在 Oracle 中,您可以使用 partitioned outer join 来填充缺失的行,然后您可以仅选择这些行
select g.group_col,t.tenant
from groups g partition by (group_col)
right outer join tenants t on t.tenant = g.tenant
where g.tenant is null
,
我通过使用 cross join
生成所有行然后删除存在的行来解决这个问题。以下是标准 SQL,适用于 Oracle 和 Postgres:
select g.group_id,t.tenant
from tenants t cross join
(select distinct group_id from groups) g left join
groups g2
using (tenant,group_id)
where g2.tenant is null;
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