实现删除主表数据时, 判断与之关联的外键表是否有数据引用, 有标志, 无则删除_数据库技巧

问题描述：
某个基础信息表，与系统中30多个表存在外键关系，当删除基础数据时，需要判断是否已经被用过，如果用过则更改标志位，如果没有用过则直接删除，如何能很好实现这个处理？最好能够自动适应表的变化

问题解决（SQL Server 2005）
-- SQL Server 2005的错误处理容易控制, 因此，SQL Server 2005中可以直接删除, 通过错误处理来确定是否需要更新.

-- 示例如下.
USE tempdb
GO

CREATE TABLE m(
    id int PRIMARY KEY,
    bz bit)
INSERT m SELECT 1, 0
UNION ALL SELECT 2, 0

CREATE TABLE c(
    id int primary key,
    a_id int references m(id)
        ON DELETE NO ACTION)
INSERT c SELECT 1, 1
GO

-- 删除处理存储过程
CREATE PROC dbo.p_delete
    @id int
AS
SET NOCOUNT ON
BEGIN TRY
BEGIN TRAN
    DELETE FROM m WHERE id = @id
COMMIT TRAN
END TRY
BEGIN CATCH
    ROLLBACK TRAN
    IF ERROR_NUMBER() = 547 -- 如果是外键约束错误
    BEGIN
        BEGIN TRY
        BEGIN TRAN          -- 更新标志
            UPDATE m SET bz = 1
            WHERE id = @id
        COMMIT TRAN
        END TRY
        BEGIN CATCH
            SELECT ERROR_NUMBER(), ERROR_MESSAGE()
        END CATCH
    END
    ELSE
        SELECT ERROR_NUMBER(), ERROR_MESSAGE()
END CATCH
GO

-- 调用
EXEC dbo.p_delete 1
EXEC dbo.p_delete 2
SELECT * FROM m
SELECT * FROM c
GO

DROP TABLE c, m
DROP PROC dbo.p_delete

问题解决（SQL Server 2000）
-- SQL Server 2000 对错误处理不好控制, 一般还是建议做判断
-- 通过系统表查询系统表，可以获取某个表关联的所有外键表

-- 示例存储过程
CREATE PROC dbo.p_Delete
    @tbname sysname,        -- 基础数据表名
    @PkFieldName sysname,   -- 基础数据表关键字段名
    @PkValue int            -- 要删除的基础数据表关键字值
AS
SET NOCOUNT ON
DECLARE @bz bit, @s nvarchar(4000)
DECLARE tb CURSOR LOCAL
FOR
SELECT N'
SET @bz = CASE WHEN EXISTS(
        SELECT * FROM ' + QUOTENAME(@tbname)
        + N' A, ' + QUOTENAME(OBJECT_NAME(B.fkeyid))
        + N' B
        WHERE A.' + QUOTENAME((SELECT name FROM syscolumns WHERE colid = B.rkey AND id = B.rkeyid))
        + N' = B.' + QUOTENAME((SELECT name FROM syscolumns WHERE colid = B.fkey AND id = B.fkeyid))
        + N' AND A.' + QUOTENAME((SELECT name FROM syscolumns WHERE colid = B.rkey AND id = B.rkeyid))
        + N' = @id) THEN 1 ELSE 0 END'
FROM sysobjects A
    JOIN sysforeignkeys B
        ON A.id= B.constid
    JOIN sysobjects C
        ON A.parent_obj = C.id
WHERE A.xtype = 'f'
    AND C.xtype = 'U'
    AND OBJECT_NAME(B.rkeyid) = @tbname
OPEN tb
FETCH tb INTO @s
WHILE @@FETCH_STATUS = 0
BEGIN
    EXEC sp_executesql @s, N'@tbname sysname, @id int, @bz bit OUT', @tbname, @PkValue, @bz OUT
    IF @bz = 1
    BEGIN
        SET @s = N'UPDATE ' + QUOTENAME(@tbname)
            + N' SET bz = 1 WHERE ' + QUOTENAME(@PkFieldName)
            + N' = @id'
        EXEC sp_executesql @s, N'@id int', @PkValue

        RETURN
    END

    FETCH tb INTO @s
END
CLOSE tb
DEALLOCATE tb

SET @s = N'DELETE FROM ' + QUOTENAME(@tbname)
    + N' WHERE ' + QUOTENAME(@PkFieldName)
    + N' = @id'
EXEC sp_executesql @s, N'@id int', @PkValue
GO

注意事项
设置表的主/外键关系的时候，不要设置级联删除（ON DELETE CASCADE）