如何查找特定行的外键依赖项？

Question

如果我有一张桌子,TableA:

Id
1
2
3
...

还有另外两张桌子:

表B:

Id, TableAId
1   1
2   1

表C:

Id, TableAId
1,  1
2,  2

TableAId与TableA.Id的FK关系.

如何确定TableA,Id 1有三行指向它？那个TableA,Id 2有一行指向它吗？更具体地说,我如何识别这些行是什么？(他们的表名和Id)

Answer 1

您可以使用INFORMATION_SCHEMA视图生成select语句以显示相关行.我只针对问题中提供的表对此进行了测试,但是可以扩展为在密钥为多列的情况下.

declare @table_schema nvarchar(50) = 'dbo',
        @table_name nvarchar(50) = 'TableA',
        @id int = 1

select fk_col.TABLE_SCHEMA, fk_col.TABLE_NAME, fk_col.COLUMN_NAME, 
    'select * from ' + fk_col.TABLE_SCHEMA + '.' + fk_col.TABLE_NAME + ' t1 '
        + ' inner join ' + @table_schema + '.' + @table_name + ' t2 '
        + ' on t1.' + fk_col.COLUMN_NAME + ' = t2.' + pk_col.COLUMN_NAME
        + ' where t2.' + pk_col.COLUMN_NAME + ' = ' + cast(@id as nvarchar)

from INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk

    join INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE pk_col
        on pk.CONSTRAINT_SCHEMA = pk_col.CONSTRAINT_SCHEMA
        and pk.CONSTRAINT_NAME = pk_col.CONSTRAINT_NAME

    join INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS fk 
        on pk.CONSTRAINT_SCHEMA = fk.UNIQUE_CONSTRAINT_SCHEMA 
        and pk.CONSTRAINT_NAME = fk.UNIQUE_CONSTRAINT_NAME

    join INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE fk_col
        on fk_col.CONSTRAINT_SCHEMA = fk.CONSTRAINT_SCHEMA
        and fk_col.CONSTRAINT_NAME = fk.CONSTRAINT_NAME

where pk.TABLE_SCHEMA = @table_schema 
    and pk.TABLE_NAME = @table_name
    and pk.CONSTRAINT_TYPE = 'PRIMARY KEY'

生成的select语句:

select * from dbo.TableB t1  inner join dbo.TableA t2  on t1.TableAId = t2.Id where t2.Id = 1
select * from dbo.TableC t1  inner join dbo.TableA t2  on t1.TableAId = t2.Id where t2.Id = 1

和查询结果:

Id          TableAId    Id
----------- ----------- -----------
1           1           1
2           1           1

Id          TableAId    Id
----------- ----------- -----------
1           1           1