SQL Server：删除所有数据库表中的所有 Not Null 约束

Question

如何使用 SQL Server 删除每个表的所有列中的所有非空约束？

希望在所有表和列中循环运行此查询， How to remove not null constraint in sql server using query

注意：要求适用于所有非主键列。

类似问题：

How to drop all Foreign Key constraints in all tables?

Answer 1

您可以使用以下查询为每列生成更改语句。 并使用生成的语句来更改表。 这不会改变主键列，但不会考虑其他外键约束。

DECLARE @Sql NVARCHAR(MAX) = ''

SELECT @Sql +=  CONCAT(N'ALTER TABLE '
, QUOTENAME(schema_name(t.schema_id))
, N'.', QUOTENAME(t.name) 
, N' ALTER COLUMN '
, QUOTENAME(c.Name
), N' '
,Type_name(c.user_type_id) + CASE 
        --types without length, precision, or scale specifiecation 
        WHEN Type_name(c.user_type_id) IN (
                N'int'
                ,N'bigint'
                ,N'smallint'
                ,N'tinyint'
                ,N'money'
                ,N'smallmoney'
                ,N'real'
                ,N'datetime'
                ,N'smalldatetime'
                ,N'bit'
                ,N'image'
                ,N'text'
                ,N'uniqueidentifier'
                ,N'date'
                ,N'ntext'
                ,N'sql_variant'
                ,N'hierarchyid'
                ,N'geography'
                ,N'geometry'
                ,N'timestamp'
                ,N'xml'
                )
            THEN N''
                --types with precision and scale specification 
        WHEN Type_name(c.user_type_id) IN (
                N'decimal'
                ,N'numeric'
                )
            THEN N'(' + Cast(c.PRECISION AS VARCHAR(5)) + N',' + Cast(c.scale AS VARCHAR(5)) + N')'
                --types with scale specification only 
        WHEN Type_name(c.user_type_id) IN (
                N'time'
                ,N'datetime2'
                ,N'datetimeoffset'
                )
            THEN N'(' + Cast(c.scale AS VARCHAR(5)) + N')'
                --float default precision is 53 - add precision when column has a different precision value 
        WHEN Type_name(c.user_type_id) IN (N'float')
            THEN CASE 
                    WHEN c.PRECISION = 53
                        THEN N''
                    ELSE N'(' + Cast(c.PRECISION AS VARCHAR(5)) + N')'
                    END
                --types with length specifiecation 
        ELSE N'(' + CASE ic.CHARACTER_MAXIMUM_LENGTH
                WHEN -1
                    THEN N'MAX'
                ELSE Cast(ic.CHARACTER_MAXIMUM_LENGTH AS NVARCHAR(20))
                END + N')'
        END + CASE 
        WHEN c.is_filestream = 1
            THEN N' FILESTREAM'
        ELSE N''
        END + COALESCE(N' COLLATE ' + c.collation_name, N'') + CASE 
        WHEN c.is_sparse = 1
            THEN N' SPARSE'
        ELSE N''
        END + CASE 
        WHEN c.is_rowguidcol = 1
            THEN N' ROWGUIDCOL'
        ELSE N''
        END
, N' NULL', '
GO
'  )
FROM sys.tables t
INNER JOIN sys.columns c on c.object_Id = t.object_Id
INNER JOIN INFORMATION_SCHEMA.COLUMNS  ic on ic.TABLE_SCHEMA = Schema_name(t.schema_id)
    AND ic.TABLE_NAME = t.name
    AND ic.COLUMN_NAME = c.name
WHERE c.is_nullable = 0
-- And is not part of the primary key
AND NOT EXISTS (
    SELECT 1
    FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS cons
    INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS K ON cons.TABLE_NAME = K.TABLE_NAME
        AND cons.CONSTRAINT_CATALOG = K.CONSTRAINT_CATALOG
        AND cons.CONSTRAINT_SCHEMA = K.CONSTRAINT_SCHEMA
        AND cons.CONSTRAINT_NAME = K.CONSTRAINT_NAME
    WHERE cons.CONSTRAINT_TYPE = 'PRIMARY KEY'
    AND k.COLUMN_NAME = c.Name
    AND k.TABLE_NAME = t.Name
    AND k.TABLE_SCHEMA = ic.TABLE_SCHEMA
)


-- PRINT(@SQL)
-- Execute the generated alter table statements
EXEC (@SQL)