sql - 如何使用 INFORMATION_SCHEMA 找到默认约束？

Question

我正在尝试测试是否存在给定的默认约束。我不想使用 sysobjects 表，而是更标准的 INFORMATION_SCHEMA。

我以前用它来检查表和主键约束，但我在任何地方都看不到默认约束。

他们不在那里吗？（我使用的是 MS SQL Server 2000）。

编辑：我正在寻找约束的名称。

score 137 · Accepted Answer

据我了解，默认值约束不是 ISO 标准的一部分，因此它们不会出现在 INFORMATION_SCHEMA 中。INFORMATION_SCHEMA 似乎是此类任务的最佳选择，因为它是跨平台的，但如果信息不可用，则应使用对象目录视图 (sys.*) 而不是 SQL Server 中已弃用的系统表视图2005 年及以后。

以下与@user186476 的答案几乎相同。它返回给定列的默认值约束的名称。（对于非 SQL Server 用户，您需要默认名称才能删除它，如果您自己不命名默认约束，SQL Server 会创建一些疯狂的名称，例如“DF_TableN_Colum_95AFE4B5”。为了更容易更改您将来的架构，始终明确命名您的约束！）

-- returns name of a column's default value constraint 
SELECT
    default_constraints.name
FROM 
    sys.all_columns

        INNER JOIN
    sys.tables
        ON all_columns.object_id = tables.object_id

        INNER JOIN 
    sys.schemas
        ON tables.schema_id = schemas.schema_id

        INNER JOIN
    sys.default_constraints
        ON all_columns.default_object_id = default_constraints.object_id

WHERE 
        schemas.name = 'dbo'
    AND tables.name = 'tablename'
    AND all_columns.name = 'columnname'

score 47 · Accepted Answer

通过指定与默认约束相关的表名和列名，您可以使用以下内容进一步缩小结果范围：

select * from sysobjects o 
inner join syscolumns c
on o.id = c.cdefault
inner join sysobjects t
on c.id = t.id
where o.xtype = 'D'
and c.name = 'Column_Name'
and t.name = 'Table_Name'

score 41 · Accepted Answer

Information_Schema视图中似乎没有默认约束名称。

用于SELECT * FROM sysobjects WHERE xtype = 'D' AND name = @name 按名称查找默认约束

score 14 · Accepted Answer

下面的脚本列出了运行它的数据库中用户表的所有默认约束和默认值：

SELECT  
        b.name AS TABLE_NAME,
        d.name AS COLUMN_NAME,
        a.name AS CONSTRAINT_NAME,
        c.text AS DEFAULT_VALUE
FROM sys.sysobjects a INNER JOIN
        (SELECT name, id
         FROM sys.sysobjects 
         WHERE xtype = 'U') b on (a.parent_obj = b.id)
                      INNER JOIN sys.syscomments c ON (a.id = c.id)
                      INNER JOIN sys.syscolumns d ON (d.cdefault = a.id)                                          
 WHERE a.xtype = 'D'        
 ORDER BY b.name, a.name

score 8 · Accepted Answer

如果您想通过列名或表名获取约束，或者您想获取数据库中的所有约束，请查看其他答案。但是，如果您只是在寻找问题的确切内容，即“测试给定的默认约束是否存在......通过约束的名称”，那么有一个更简单的方法。

sysobjects这是一个完全不使用 the或其他sys表的面向未来的答案：

IF object_id('DF_CONSTRAINT_NAME', 'D') IS NOT NULL BEGIN
   -- constraint exists, work with it.
END

score 3 · Accepted Answer

select c.name, col.name from sys.default_constraints c
    inner join sys.columns col on col.default_object_id = c.object_id
    inner join sys.objects o  on o.object_id = c.parent_object_id
    inner join sys.schemas s on s.schema_id = o.schema_id
where s.name = @SchemaName and o.name = @TableName and col.name = @ColumnName

score 2 · Accepted Answer

2

INFORMATION_SCHEMA.COLUMNS 的 COLUMN_DEFAULT 列是您要查找的内容吗？

于 2008-09-26T20:38:17.133 回答

score 2 · Accepted Answer

死灵术。
如果您只需要检查是否存在默认约束
（默认约束可能在管理不善的数据库中具有不同的名称），请
使用 INFORMATION_SCHEMA.COLUMNS (column_default)：

IF NOT EXISTS(
    SELECT * FROM INFORMATION_SCHEMA.COLUMNS
    WHERE (1=1) 
    AND TABLE_SCHEMA = 'dbo' 
    AND TABLE_NAME = 'T_VWS_PdfBibliothek' 
    AND COLUMN_NAME = 'PB_Text'
    AND COLUMN_DEFAULT IS NOT NULL  
)
BEGIN 
    EXECUTE('ALTER TABLE dbo.T_VWS_PdfBibliothek 
                ADD CONSTRAINT DF_T_VWS_PdfBibliothek_PB_Text DEFAULT (N''image'') FOR PB_Text; 
    '); 
END

如果您只想通过约束名称进行检查：

-- Alternative way: 
IF OBJECT_ID('DF_CONSTRAINT_NAME', 'D') IS NOT NULL 
BEGIN
    -- constraint exists, deal with it.
END

最后但同样重要的是，您可以创建一个名为
INFORMATION_SCHEMA.DEFAULT_CONSTRAINTS 的视图：

CREATE VIEW INFORMATION_SCHEMA.DEFAULT_CONSTRAINTS 
AS 
SELECT 
     DB_NAME() AS CONSTRAINT_CATALOG 
    ,csch.name AS CONSTRAINT_SCHEMA
    ,dc.name AS CONSTRAINT_NAME 
    ,DB_NAME() AS TABLE_CATALOG 
    ,sch.name AS TABLE_SCHEMA 
    ,syst.name AS TABLE_NAME 
    ,sysc.name AS COLUMN_NAME 
    ,COLUMNPROPERTY(sysc.object_id, sysc.name, 'ordinal') AS ORDINAL_POSITION 
    ,dc.type_desc AS CONSTRAINT_TYPE 
    ,dc.definition AS COLUMN_DEFAULT 

    -- ,dc.create_date 
    -- ,dc.modify_date 
FROM sys.columns AS sysc -- 46918 / 3892 with inner joins + where 
-- FROM sys.all_columns AS sysc -- 55429 / 3892 with inner joins + where 

INNER JOIN sys.tables AS syst 
    ON syst.object_id = sysc.object_id 

INNER JOIN sys.schemas AS sch
    ON sch.schema_id = syst.schema_id 

INNER JOIN sys.default_constraints AS dc 
    ON sysc.default_object_id = dc.object_id

INNER JOIN sys.schemas AS csch
    ON csch.schema_id = dc.schema_id 

WHERE (1=1) 
AND dc.is_ms_shipped = 0 

/*
WHERE (1=1) 
AND sch.name = 'dbo'
AND syst.name = 'tablename'
AND sysc.name = 'columnname'
*/

score 1 · Accepted Answer

WHILE EXISTS( 
    SELECT * FROM  sys.all_columns 
    INNER JOIN sys.tables ST  ON all_columns.object_id = ST.object_id
    INNER JOIN sys.schemas ON ST.schema_id = schemas.schema_id
    INNER JOIN sys.default_constraints ON all_columns.default_object_id = default_constraints.object_id
    WHERE 
    schemas.name = 'dbo'
    AND ST.name = 'MyTable'
)
BEGIN 
DECLARE @SQL NVARCHAR(MAX) = N'';

SET @SQL = (  SELECT TOP 1
     'ALTER TABLE ['+  schemas.name + '].[' + ST.name + '] DROP CONSTRAINT ' + default_constraints.name + ';'
   FROM 
      sys.all_columns

         INNER JOIN
      sys.tables ST
         ON all_columns.object_id = ST.object_id

         INNER JOIN 
      sys.schemas
         ON ST.schema_id = schemas.schema_id

         INNER JOIN
      sys.default_constraints
         ON all_columns.default_object_id = default_constraints.object_id

   WHERE 
         schemas.name = 'dbo'
      AND ST.name = 'MyTable'
      )
   PRINT @SQL
   EXECUTE sp_executesql @SQL 

   --End if Error 
   IF @@ERROR <> 0 
   BREAK
END

score 0 · Accepted Answer

我认为它不在 INFORMATION_SCHEMA 中 - 您可能必须使用 sysobjects 或相关的已弃用表/视图。

你会认为在 INFORMATION_SCHEMA.TABLE_CONSTRAINTS 中会有这样的类型，但我没有看到。

score 0 · Accepted Answer

可能是因为在其他一些 SQL DBMS 上，“默认约束”并不是真正的约束，您不会在“INFORMATION_SCHEMA.TABLE_CONSTRAINTS”中找到它的名称，所以最好的选择是“INFORMATION_SCHEMA.COLUMNS”，正如其他人已经提到的那样。

（这里是 SQLServer-ignoramus）

当您必须知道“默认约束”的名称时，我能想到的唯一原因是 SQLServer 不支持"ALTER TABLE xxx ALTER COLUMN yyy SET DEFAULT..."命令。但是，您已经处于非标准区域，您必须使用特定于产品的方式来获得所需的东西。

score 0 · Accepted Answer

如何使用 CHECK_CONSTRAINTS 和 CONSTRAINT_COLUMN_USAGE 的组合：

    select columns.table_name,columns.column_name,columns.column_default,checks.constraint_name
          from information_schema.columns columns
             inner join information_schema.constraint_column_usage usage on 
                  columns.column_name = usage.column_name and columns.table_name = usage.table_name
             inner join information_schema.check_constraints checks on usage.constraint_name = checks.constraint_name
    where columns.column_default is not null

score 0 · Accepted Answer

我正在使用以下脚本来检索所有默认值（sp_binddefaults）和所有默认约束以及以下脚本：

SELECT 
    t.name AS TableName, c.name AS ColumnName, SC.COLUMN_DEFAULT AS DefaultValue, dc.name AS DefaultConstraintName
FROM  
    sys.all_columns c
    JOIN sys.tables t ON c.object_id = t.object_id
    JOIN sys.schemas s ON t.schema_id = s.schema_id
    LEFT JOIN sys.default_constraints dc ON c.default_object_id = dc.object_id
    LEFT JOIN INFORMATION_SCHEMA.COLUMNS SC ON (SC.TABLE_NAME = t.name AND SC.COLUMN_NAME = c.name)
WHERE 
    SC.COLUMN_DEFAULT IS NOT NULL
    --WHERE t.name = '' and c.name = ''

score 0 · Accepted Answer

对象目录视图：sys.default_constraints

信息模式视图INFORMATION_SCHEMA符合 ANSI，但默认约束不是 ISO 标准的一部分。Microsoft SQL Server 提供系统目录视图以获取有关 SQL Server 对象元数据的信息。

sys.default_constraints系统目录视图用于获取有关默认约束的信息。

SELECT so.object_id TableName,
       ss.name AS TableSchema,
       cc.name AS Name,
       cc.object_id AS ObjectID,              
       sc.name AS ColumnName,
       cc.parent_column_id AS ColumnID,
       cc.definition AS Defination,
       CONVERT(BIT,
               CASE cc.is_system_named
                   WHEN 1
                   THEN 1
                   ELSE 0
               END) AS IsSystemNamed,
       cc.create_date AS CreationDate,
       cc.modify_date AS LastModifiednDate
FROM sys.default_constraints cc WITH (NOLOCK)
     INNER JOIN sys.objects so WITH (NOLOCK) ON so.object_id = cc.parent_object_id
     LEFT JOIN sys.schemas ss WITH (NOLOCK) ON ss.schema_id = so.schema_id
     LEFT JOIN sys.columns sc WITH (NOLOCK) ON sc.column_id = cc.parent_column_id
                                               AND sc.object_id = cc.parent_object_id
ORDER BY so.name,
         cc.name;

score 0 · Accepted Answer

一种更清洁的方法来做到这一点：

SELECT DC.[name]
  FROM [sys].[default_constraints] AS DC
  WHERE DC.[parent_object_id] = OBJECT_ID('[Schema].[TableName]')

sql - 如何使用 INFORMATION_SCHEMA 找到默认约束？

15 回答 15

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