SQL UNIQUE constraint enables the column to be free from redundant values. It helps restrict the input values to be unique. Thus, by applying a UNIQUE constraint to a column or a set of columns, we ensure that the data contains no Duplicate entries within it. SQL UNIQUE约束使列中没有多余...
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...
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,
UNIQUE A constraint that provides entity integrity for a specified column or columns through a unique index. A table can have multiple UNIQUE constraints. UNIQUE can't be specified for CLR table-valued functions. CLUSTERED | NONCLUSTERED Indicate that a clustered or a nonclustered index is created...
compression; however, compression is not compatible with sparse columns. Lesson 2: Implementing Constraints Quick Check 1. What is the difference between a primary key and a unique constraint? 2. What restrictions does the parent table have when creating a foreign key?
( logical_expression ) ] <column_set_definition> ::= column_set_name XML COLUMN_SET FOR ALL_SPARSE_COLUMNS ::= [ CONSTRAINT constraint_name ] { { PRIMARY KEY | UNIQUE } [ CLUSTERED | NONCLUSTERED ] ( column_name [ ASC | DESC ] [ ,... n ] ) [ WITH FILLFACTOR = fillfactor...
UNIQUE A constraint that provides entity integrity for a specified column or columns through a unique index. A table can have multiple UNIQUE constraints. UNIQUE can't be specified for CLR table-valued functions. CLUSTERED | NONCLUSTERED Indicate that a clustered or a nonclustered index is created...
USE of ALTER to ADD CHECK constraint in an already created table 在已创建的表中使用ALTER来添加CHECK约束 1) For single column ALTER TABLE company ADD CHECK (E_Id>0); 1. 2) For multiple columns ALTER TABLE company ADD CONSTRAINT chk_emp CHECK (E_Id>0AND E_name='Bharti'); ...
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.Collections.Generic.IList...
For more information, see FILESTREAM (SQL Server). SQL Copy UPDATE Archive.dbo.Records SET [Chart] = CAST('Xray 1' as VARBINARY(max)) WHERE [SerialNumber] = 2; Updating User-defined Types The following examples modify values in CLR user-defined type (UDT) columns. Three methods are ...