sql - 如何在 T-SQL 中删除默认值或类似约束？

Question

我知道语法:

ALTER TABLE [TheTable] DROP CONSTRAINT [TheDefaultConstraint]

但是当我不知道默认约束的名称时如何删除它？ (也就是说，它是在 CREATE TABLE 时自动生成的。)

Answer 1

您可以使用此代码自动执行此操作:

DECLARE @tableName VARCHAR(MAX) = '<MYTABLENAME>'
DECLARE @columnName VARCHAR(MAX) = '<MYCOLUMNAME>'
DECLARE @ConstraintName nvarchar(200)
SELECT @ConstraintName = Name 
FROM SYS.DEFAULT_CONSTRAINTS
WHERE PARENT_OBJECT_ID = OBJECT_ID(@tableName) 
AND PARENT_COLUMN_ID = (
    SELECT column_id FROM sys.columns
    WHERE NAME = @columnName AND object_id = OBJECT_ID(@tableName))
IF @ConstraintName IS NOT NULL
    EXEC('ALTER TABLE '+@tableName+' DROP CONSTRAINT ' + @ConstraintName)

只需替换 <MYTABLENAME>和<MYCOLUMNNAME>视情况而定。