CREATE TABLE Employees : Specifies the creation of a new table named Employees.EmployeeID INT PRIMARY KEY : Defines the EmployeeID column as an integer and sets it as the primary key to ensure each record is un
SQL UNIQUE Constraint on ALTER TABLE
Explore all SQL constraints with examples and real-world use cases. Learn PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, and more.
SQL PRIMARY KEY Constraint on CREATE TABLE 下面的 SQL 在“Persons” 表创建时在 “Id_P” 列创建 PRIMARY KEY 约束: MySQL: CREATETABLEPersons(Id_PintNOTNULL,LastNamevarchar(255)NOTNULL,FirstNamevarchar(255),Addressvarchar(255),Cityvarchar(255),PRIMARYKEY(Id_P)) 1. 2. 3. 4. 5. 6. 7. ...
We can implement theUNIQUEconstraint at the time of table creation. For example, -- create a table with unique constraintCREATETABLEColleges ( college_idINTNOTNULLUNIQUE, college_codeVARCHAR(20)UNIQUE, college_nameVARCHAR(50) );-- insert values to Colleges tableINSERTINTOColleges(college_id, coll...
If the name of a history table is specified during history table creation, you must specify the schema and table name. If the history table doesn't exist, the system generates a new history table matching the schema of the current table in the same filegroup as the current table, creating...
If the name of a history table is specified during history table creation, you must specify the schema and table name. If the history table doesn't exist, the system generates a new history table matching the schema of the current table in the same filegroup as the current table, creating...
protected virtual void CreateTableConstraints(Microsoft.EntityFrameworkCore.Migrations.Operations.CreateTableOperation operation, Microsoft.EntityFrameworkCore.Metadata.IModel? model, Microsoft.EntityFrameworkCore.Migrations.MigrationCommandListBuilder builder); 参数 operation CreateTableOperation 操作...
int, bigint, decimal(p,0), or numeric(p,0) columns. Only one identity column can be created per table. Bound defaults and DEFAULT constraints cannot be used with an identity column. Both the seed and increment or neither must be specified. If neither is specified, the default is (1,1...
1.3:Creating aTable with aForeign Key Reference 1.4:Adding aForeign Key to an Existing Table 1.5:Allowing Cascading Changes in Foreign Keys 2:Surrogate Keys 3:Constraints 3.1:Creating a Unique Constraint 3.2:Using CHECK Constraints 1:Keys