我从来没有为SQL Server“手工编写”对象创建代码，外键声明在SQL Server和Postgres之间似乎是不同的。这是我的sql到目前为止:
drop table exams;
drop table question_bank;
drop table anwser_bank;
create table exams
(
exam_id uniqueidentifier primary key,
exam_name varchar(50),
);
create table question_bank
(
question_id uniqueidentifier primary key,
question_exam_id uniqueidentifier not null,
question_text varchar(1024) not null,
question_point_value decimal,
constraint question_exam_id foreign key references exams(exam_id)
);
create table anwser_bank
(
anwser_id uniqueidentifier primary key,
anwser_question_id uniqueidentifier,
anwser_text varchar(1024),
anwser_is_correct bit
);
当我运行查询时，我得到这个错误:
信息8139,16级，状态0,9号线
中的引用列数
外键与number of不同
引用列、表
“question_bank”。
你能发现错误吗?
Necromancing。
实际上，正确地做这个有点棘手。
首先需要检查要将外键设置为引用的列的主键是否存在。
在本例中，创建表T_ZO_SYS_Language_Forms上的外键，引用dbo.T_SYS_Language_Forms.LANG_UID
-- First, chech if the table exists...
IF 0 < (
SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_TYPE = 'BASE TABLE'
AND TABLE_SCHEMA = 'dbo'
AND TABLE_NAME = 'T_SYS_Language_Forms'
)
BEGIN
-- Check for NULL values in the primary-key column
IF 0 = (SELECT COUNT(*) FROM T_SYS_Language_Forms WHERE LANG_UID IS NULL)
BEGIN
ALTER TABLE T_SYS_Language_Forms ALTER COLUMN LANG_UID uniqueidentifier NOT NULL
-- No, don't drop, FK references might already exist...
-- Drop PK if exists
-- ALTER TABLE T_SYS_Language_Forms DROP CONSTRAINT pk_constraint_name
--DECLARE @pkDropCommand nvarchar(1000)
--SET @pkDropCommand = N'ALTER TABLE T_SYS_Language_Forms DROP CONSTRAINT ' + QUOTENAME((SELECT CONSTRAINT_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
--WHERE CONSTRAINT_TYPE = 'PRIMARY KEY'
--AND TABLE_SCHEMA = 'dbo'
--AND TABLE_NAME = 'T_SYS_Language_Forms'
----AND CONSTRAINT_NAME = 'PK_T_SYS_Language_Forms'
--))
---- PRINT @pkDropCommand
--EXECUTE(@pkDropCommand)
-- Instead do
-- EXEC sp_rename 'dbo.T_SYS_Language_Forms.PK_T_SYS_Language_Forms1234565', 'PK_T_SYS_Language_Forms';
-- Check if they keys are unique (it is very possible they might not be)
IF 1 >= (SELECT TOP 1 COUNT(*) AS cnt FROM T_SYS_Language_Forms GROUP BY LANG_UID ORDER BY cnt DESC)
BEGIN
-- If no Primary key for this table
IF 0 =
(
SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE CONSTRAINT_TYPE = 'PRIMARY KEY'
AND TABLE_SCHEMA = 'dbo'
AND TABLE_NAME = 'T_SYS_Language_Forms'
-- AND CONSTRAINT_NAME = 'PK_T_SYS_Language_Forms'
)
ALTER TABLE T_SYS_Language_Forms ADD CONSTRAINT PK_T_SYS_Language_Forms PRIMARY KEY CLUSTERED (LANG_UID ASC)
;
-- Adding foreign key
IF 0 = (SELECT COUNT(*) FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS WHERE CONSTRAINT_NAME = 'FK_T_ZO_SYS_Language_Forms_T_SYS_Language_Forms')
ALTER TABLE T_ZO_SYS_Language_Forms WITH NOCHECK ADD CONSTRAINT FK_T_ZO_SYS_Language_Forms_T_SYS_Language_Forms FOREIGN KEY(ZOLANG_LANG_UID) REFERENCES T_SYS_Language_Forms(LANG_UID);
END -- End uniqueness check
ELSE
PRINT 'FSCK, this column has duplicate keys, and can thus not be changed to primary key...'
END -- End NULL check
ELSE
PRINT 'FSCK, need to figure out how to update NULL value(s)...'
END
我喜欢AlexCuse的答案，但是无论何时添加外键约束，都应该注意如何处理对引用表中一行中的引用列的更新，特别是如何处理对引用表中的行删除。
如果约束是这样创建的:
alter table MyTable
add constraint MyTable_MyColumn_FK FOREIGN KEY ( MyColumn )
references MyOtherTable(PKColumn)
. .然后，如果引用表中有相应的行，则引用表中的更新或删除将失败并报错。
这可能是你想要的行为，但根据我的经验，它通常不是。
如果你像这样创建它:
alter table MyTable
add constraint MyTable_MyColumn_FK FOREIGN KEY ( MyColumn )
references MyOtherTable(PKColumn)
on update cascade
on delete cascade
．．然后，父表中的更新和删除将导致引用表中相应行的更新和删除。
(我并不是建议修改默认值，默认值过于谨慎，这是好的。我只是说，这是一个创造约束的人应该经常注意的事情。)
顺便说一下，这可以在创建表时完成，就像这样:
create table ProductCategories (
Id int identity primary key,
ProductId int references Products(Id)
on update cascade on delete cascade
CategoryId int references Categories(Id)
on update cascade on delete cascade
)
