如何解决哪些SQL数据库在CHECK约束中支持子查询？
| 哪些SQL数据库（如果有）支持CHECK约束中的子查询？ 目前，据我所知，Oracle，MySQL和PostgreSQL还没有。 编辑 （根据初始答案进行澄清。）我正在寻找这样的东西：CREATE TABLE personnel (
...,department VARCHAR(64) NOT NULL,salary NUMERIC NOT NULL,CHECK (salary >= (SELECT MIN(p.salary) FROM payranges p WHERE p.dept = department)
AND
salary <= (SELECT MAX(p.salary) FROM payranges p WHERE p.dept = department)
)
解决方法
Access数据库引擎（ACE，Jet等）在
CHECK
CHECK
CREATE TABLE T1
(
c INTEGER NOT NULL UNIQUE
);
ALTER TABLE T1 ADD
CONSTRAINT max_two_rows
CHECK (
NOT EXISTS (
SELECT 1
FROM T1 AS T
HAVING COUNT(*) > 2
)
);
CREATE TABLE T2
(
c INTEGER NOT NULL UNIQUE
);
ALTER TABLE T2 ADD
CONSTRAINT exactly_two_rows
CHECK (
NOT EXISTS (
SELECT 1
FROM T2 AS T
HAVING COUNT(*) <> 2
)
);
T1
SELECT DT1.c
FROM (
SELECT DISTINCT 1 AS c
FROM T1
UNION ALL
SELECT DISTINCT 2
FROM T1
) AS DT1;
Sub AccessCheckSubqueryButProblem()
On Error Resume Next
Kill Environ$(\"temp\") & \"\\DropMe.mdb\"
On Error GoTo 0
Dim cat
Set cat = CreateObject(\"ADOX.Catalog\")
With cat
.Create _
\"Provider=Microsoft.Jet.OLEDB.4.0;\" & _
\"Data Source=\" & _
Environ$(\"temp\") & \"\\DropMe.mdb\"
With .ActiveConnection
Dim Sql As String
Sql = _
\"CREATE TABLE T1 \" & vbCr & _
\"( \" & vbCr & _
\" c INTEGER NOT NULL UNIQUE \" & vbCr & _
\");\"
.Execute Sql
Sql = _
\"ALTER TABLE T1 ADD \" & vbCr & _
\" CONSTRAINT max_two_rows \" & vbCr & _
\" CHECK ( \" & vbCr & _
\" NOT EXISTS ( \" & vbCr & _
\" SELECT 1 \" & vbCr & _
\" FROM T1 AS T \" & vbCr & _
\" HAVING COUNT(*) > 2 \" & vbCr & _
\" ) \" & vbCr & _
\" );\"
.Execute Sql
Sql = _
\"INSERT INTO T1 (c) VALUES (1);\"
.Execute Sql
Sql = _
\"INSERT INTO T1 (c) VALUES (2);\"
.Execute Sql
\' The third row should (and does)
\' cause the CHECK to bite
On Error Resume Next
Sql = _
\"INSERT INTO T1 (c) VALUES (3);\"
.Execute Sql
MsgBox Err.Description
On Error GoTo 0
Sql = _
\"CREATE TABLE T2 \" & vbCr & _
\"( \" & vbCr & _
\" c INTEGER NOT NULL UNIQUE \" & vbCr & _
\");\"
.Execute Sql
Sql = _
\"ALTER TABLE T2 ADD \" & vbCr & _
\" CONSTRAINT exactly_two_rows \" & vbCr & _
\" CHECK ( \" & vbCr & _
\" NOT EXISTS ( \" & vbCr & _
\" SELECT 1 \" & vbCr & _
\" FROM T2 AS T \" & vbCr & _
\" HAVING COUNT(*) <> 2 \" & vbCr & _
\" ) \" & vbCr & _
\" );\"
.Execute Sql
\' INSERTing two rows in the same SQL statement
\' should succeed according to SQL-92
\' but fails (and we have no docs from MS
\' to indicate whether this is a bug/feature)
On Error Resume Next
Sql = _
\"INSERT INTO T2 \" & vbCr & _
\" SELECT c \" & vbCr & _
\" FROM T1;\"
.Execute Sql
MsgBox Err.Description
On Error GoTo 0
End With
Set .ActiveConnection = Nothing
End With
End Sub
ALTER TABLE Table_1 ADD CONSTRAINT constraint_1
CHECK (column_1 > (SELECT MAX(column_2) FROM Table_2) NOT DEFERRABLE;
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