sql - 如何获得对 SQL 表列的约束

Question

我的表中有一个名为MealType( VARCHAR)的列，其CHECK约束为{"Veg", "NonVeg", "Vegan"}

这将负责插入。

我想显示这些选项以供选择，但我无法找出 SQL 查询来找出表中特定列的约束。

乍一看 MS SQL 服务器中的系统表，我似乎需要使用 MS SQL 的 API 来获取信息。我希望 SQL 查询本身能够得到它。

Answer 1

最简单快捷的方法是使用：

sp_help 'TableName'

Answer 2

此查询应向您显示表上的所有约束：

select chk.definition
from sys.check_constraints chk
inner join sys.columns col
    on chk.parent_object_id = col.object_id
inner join sys.tables st
    on chk.parent_object_id = st.object_id
where 
st.name = 'Tablename'
and col.column_id = chk.parent_column_id

可以用这个替换select语句：

select substring(chk.Definition,2,3),substring(chk.Definition,9,6),substring(chk.Definition,20,5) 

Answer 3

SELECT obj_table.NAME      AS 'table', 
        columns.NAME        AS 'column',
        obj_Constraint.NAME AS 'constraint',
        obj_Constraint.type AS 'type'

    FROM   sys.objects obj_table 
        JOIN sys.objects obj_Constraint 
            ON obj_table.object_id = obj_Constraint.parent_object_id 
        JOIN sys.sysconstraints constraints 
             ON constraints.constid = obj_Constraint.object_id 
        JOIN sys.columns columns 
             ON columns.object_id = obj_table.object_id 
            AND columns.column_id = constraints.colid 
    WHERE obj_table.NAME='table_name'
    ORDER  BY 'table'

Answer 4

您可以使用

sp_helpconstraint 'tableName', 'nomsg'

获取表的所有约束。

“sp_help”返回更多信息。

Answer 5

感谢orgtrigger的示例！我对其进行了改进，以便能够删除不必要的约束（然后在需要时创建它们的修改版本）。也许这段代码对任何人都有用。

  -- removing old constraints
DECLARE @ConstraintNames TABLE (Name VARCHAR(MAX), RowNum INT)
DECLARE @TableName VARCHAR(100) = 'HubSpot'

INSERT @ConstraintNames
  SELECT [constraint].name,
         ROW_NUMBER() OVER (ORDER BY [constraint].[name]) AS RowNum
  FROM sys.default_constraints [constraint]
  INNER JOIN sys.columns col
      ON [constraint].parent_object_id = col.object_id
  INNER JOIN sys.tables st
      ON [constraint].parent_object_id = st.object_id
  WHERE 
  st.name = @TableName 
  AND col.name IN ('ForceUpdateOnImport', 'ForceUpdateOnExport')
  AND col.column_id = [constraint].parent_column_id
  
SELECT * FROM @ConstraintNames

DECLARE @i INT = 1,
        @count INT,
        @constraintName VARCHAR(MAX),
        @sql VARCHAR(MAX)
SELECT @count = COUNT(1) FROM @ConstraintNames

WHILE @i <= @count 
  BEGIN 
    SELECT @constraintName = cn.Name FROM @ConstraintNames cn WHERE cn.RowNum = @i
    SET @sql = 'ALTER TABLE ' + @TableName + ' DROP CONSTRAINT ' + @constraintName
      
    EXEC (@sql)
    SET @i = @i + 1
  END