例如,我有 3 个表:
tbl_main
-------------------------
|ID_No |Info1 |Info2 |
|------+--------+-------|
|00123 |name1 |a city |
|00567 |name2 |b city |
|00789 |name3 |c city |
-------------------------
tbl_version
--------------------------------
|ID_No |Version_Name|Version_No|
|------+------------+----------|
|00123 |version_a_01|1 |
|00567 |version_b_01|1 |
|00789 |version_c_01|1 |
--------------------------------
tbl_version_upd
--------------------------------
|ID_No |Version_Name|Version_No|
|------+------------+----------|
|00123 |version_a_02|2 |
|00123 |version_a_03|2 |
|00123 |version_a_04|4 |
|00789 |version_c_02|2 |
--------------------------------
我想根据 tbl_version 和 tbl_version_upd 中的 Version_No 获取每个 ID_No 的最新 Version_Name。
Wanted output:
--------------------------------------
|ID_No |Info1 |Info2 |Version_Name|
|------+--------+-------+------------|
|00123 |name1 |a city |version_a_04|
|00567 |name2 |b city |version_b_01|
|00789 |name3 |c city |version_c_02|
--------------------------------------
目前,我有这个查询:
Select a.ID_No, a.Info1, a.Info2, b.Version_Name
FROM tbl_main a
LEFT JOIN (tbl_version UNION ALL tbl_version_upd) b ON a.ID_No=b.ID_No
但它获取每个 ID_No 的所有版本
Current output:
--------------------------------------
|ID_No |Info1 |Info2 |Version_Name|
|------+--------+-------+------------|
|00123 |name1 |a city |version_a_01|
|00123 |name1 |a city |version_a_02|
|00123 |name1 |a city |version_a_03|
|00123 |name1 |a city |version_a_04|
|00567 |name2 |b city |version_b_01|
|00789 |name3 |c city |version_c_01|
|00789 |name3 |c city |version_c_02|
--------------------------------------
apply 是获得它的好方法,我也使用 CTE 作为联合,但只是为了可读性,子查询也能工作
;WITH allversions AS (
SELECT ID_No, Version_Name, Version_No
FROM tbl_version
UNION ALL
SELECT ID_No, Version_Name, Version_No
FROM tbl_version_upd
)
SELECT a.ID_No, a.Info1, a.Info2, b.Version_Name
FROM tbl_main a
OUTER APPLY (
SELECT TOP 1 Version_Name
FROM allversions av
WHERE av.ID_No = a.ID_No
ORDER BY Version_No DESC
) b
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我来说两句