For Multiple Columns -- add unique constraint to multiple columnsALTERTABLECollegesADDUNIQUEUnique_College (college_id, college_code); Here, the SQL command adds theUNIQUEconstraint tocollege_idandcollege_codecolumns in the existingCollegestable. Also,Unique_Collegeis a name given to theUNIQUEconstrain...
To name aUNIQUEconstraint, and to define aUNIQUEconstraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access: ALTERTABLEPersons ADDCONSTRAINTUC_PersonUNIQUE(ID,LastName); DROP a UNIQUE Constraint
To allow naming of a UNIQUE constraint, and for defining a UNIQUE constraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access: ALTERTABLEPersonsADDCONSTRAINTuc_PersonIDUNIQUE(P_Id,LastName) To DROP a UNIQUE Constraint To drop a UNIQUE constraint, us...
To create a UNIQUE constraint on the "ID" column when the table is already created, use the following SQL:MySQL / SQL Server / Oracle / MS Access:ALTER TABLE Persons ADD UNIQUE (ID); To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following ...
alter table student add constraint fk_student_ID foreign key(ID) references achievement(ID); 1. 如图: 注意,科普一下:外键不一定要是另一个表的主键(primary key:主键约束),也可以是另一个表的唯一值(unique:唯一约束)。 因为外键和另一张表所关联的字段,值是不能重复(而主键约束是一行数据的唯一标识,...
constraint UQ_userJSID_MyUserId unique,--唯一约束 varchar(20) not null, varchar(12) null, int null, int not null --用户年龄在2-120岁之间 constraint CHK_UserAge_MyUserInfo check(UserAge >2 && UserAge <120) char(2) not null --用户性别男或女 ...
--Create a rowstore table with a unique constraint. --The unique constraint is implemented as a nonclustered index. CREATE TABLE t_account ( AccountKey int NOT NULL, AccountDescription nvarchar (50), AccountType nvarchar(50), UnitSold int, CONSTRAINT uniq_account UNIQUE (AccountKey) ); -...
SQL_ISV_COLUMNS = 标识可由给定用户访问的永久性表的列。 (FIPS 过渡级别)SQL_ISV_CONSTRAINT_COLUMN_USAGE = 类似于CONSTRAINT_TABLE_USAGE视图,为给定用户拥有的各种约束标识列。 (中级)SQL_ISV_CONSTRAINT_TABLE_USAGE = 标识约束(引用、唯一和断言)使用的表,并且由给定用户拥有。 (中级)SQL_ISV_DOMAIN_...
UNIQUE DESC ON UNPIVOT DISK OPEN UPDATE DISTINCT OPENDATASOURCE UPDATETEXT DISTRIBUTED OPENQUERY USE DOUBLE OPENROWSET USER DROP OPENXML VALUES DUMP OPTION VARYING ELSE OR VIEW END ORDER WAITFOR ERRLVL OUTER WHEN ESCAPE OVER WHERE EXCEPT PERCENT ...
42823 Multiple columns are returned from a subquery that only allows one column. INVALID_SUBQUERY_EXPRESSION 42825 The rows of UNION, INTERSECT, EXCEPT, or VALUES do not have compatible columns. CANNOT_MERGE_INCOMPATIBLE_DATA_TYPE INCOMPATIBLE_COLUMN_TYPE 42826 The rows of UNION, INTERSECT, EXCEPT...