选择具有唯一值的id

Question

+----+--------+-----------+
| ID | ID_DEP | OPERATION |
+----+--------+-----------+
|  1 |      2 | T1        |
|  2 |      2 | T1        |
|  3 |      2 | T4        |
|  4 |      1 | T1        |
|  5 |      1 | T1        |
|  6 |      1 | T4        |
|  7 |      4 | T6        |
|  8 |      3 | T1        |
|  9 |      3 | T1        |
| 10 |      5 | T9        |
+----+--------+-----------+

嘿伙计们，帮我解决这个简单的问题。

如何仅从操作列中选择仅具有T1的ID（ID_DEP）而不是其他值。

Answer 1

我会使用WHERE NOT EXISTS

测试数据

IF OBJECT_ID('tempdb..#TestData') IS NOT NULL DROP TABLE #TestData
CREATE TABLE #TestData (ID int, ID_DEP int, OPERATION varchar(2))
INSERT INTO #TestData (ID, ID_DEP, OPERATION)
VALUES
 (1,2,'T1')
,(2,2,'T1')
,(3,2,'T4')
,(4,1,'T1')
,(5,1,'T1')
,(6,1,'T4')
,(7,4,'T6')
,(8,3,'T1')
,(9,3,'T1')
,(10,5,'T9')

查询

SELECT
td.*
FROM #TestData td
WHERE NOT EXISTS (SELECT 1 FROM #TestData sub WHERE sub.OPERATION <> 'T1' AND td.ID_DEP = sub.ID_DEP)

输出

ID  ID_DEP  OPERATION
8   3       T1
9   3       T1

基本上，NOT EXISTS会返回值IS NOT'T1'的所有行。如果存在ID_DEP，那么我们希望将其从结果集中排除。