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, use the following SQL: MySQL: ALTERTABLEPersonsDROPI...
-- 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 theUNIQUEconstraint defined forcollege_...
UNIQUE(ID) ); To name aUNIQUEconstraint, and to define aUNIQUEconstraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access: CREATETABLEPersons ( ID intNOTNULL, LastName varchar(255)NOTNULL,
You can apply multiple CHECK constraints to a single column. You can also apply a single CHECK constraint to multiple columns by creating it at the table level. For example, a multiple-column CHECK constraint could be used to confirm that any row with a country_region column value of USA ...
报错:Update row with Key (id)=(xxxx) multiple times或者duplicate key value violates unique constraint 问题原因:违反唯一性约束,执行UPDATE、INSERT ON CONFLICT或INSERT操作时,主键存在重复数据。 解决方法: 若INSERT语法报错:可以改为INSERT INTO xx ON CONFLICT的语法,实现主键去重,详情请参见INSERT ON CONFLIC...
error occurs if you try to add a new row with a key value that matches an existing row. If you specify a prefix value for a column in a UNIQUE index, the column values must be unique within the prefix length. A UNIQUE index permits multiple NULL values for columns that can contain ...
UniqueConstraint.Columns 屬性 文章 12/08/2011 在此文章 語法 .NET Framework 安全性 請參閱 取得條件約束資料行的清單。 命名空間:Microsoft.Data.Schema.ScriptDom.Sql 組件:Microsoft.Data.Schema.ScriptDom.Sql (在 Microsoft.Data.Schema.ScriptDom.Sql.dll 中) ...
Now you can create INDEX on multiple columns: CREATE INDEX index-name ON table_name (column1, column2, …); Dropping Constraints Any constraint that you have defined can be dropped using the ALTER TABLE command with the DROP CONSTRAINT option. ...
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_...
UniqueConstraintDefinition.Columns Property Reference Feedback Definition Namespace: Microsoft.SqlServer.TransactSql.ScriptDom Assembly: Microsoft.SqlServer.TransactSql.ScriptDom.dll Package: Microsoft.SqlServer.TransactSql.ScriptDom v161.8901.0 Represents the constraint columns. C# 复制 public System...