如何定义sql主键（How do I define the SQL primary key）.docVIP

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如何定义sql主键（How do I define the SQL primary key）.doc

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如何定义sql主键（How do I define the SQL primary key）

如何定义sql主键（How do I define the SQL primary key） How do I define the SQL primary key? Reading: 661 times: 2010-09-24 15:52:35 font: [large, medium, small] In the SQL database, how to define SQL primary key is often encountered problems, the following will introduce you two definitions of SQL primary key method, for your reference, I hope that you can help. The SQL primary key is an important attribute of the database table. Building a primary key prevents the existence of exactly the same record in the table, that is, the record value of the SQL primary key in a table is unique. There are two ways to build SQL primary keys: one is in the GUI environment provided by the database, and the other is through the execution of the SQL statement, which are described below. 1. set up in the GUI environment provided by the database (take SQL7 as an example). After entering the table information, press the Ctrl key, select multiple rows at the same time, and then click the primary key button on it. 2. perform the creation by the SQL statement. There are two types, one is to write directly in the build statement, and the other is to change the table structure after setting up the table. Two. Write directly in the build statement: Create Table table name (field name 1, Int, Not, Null, Field name 2, nvarchar (13) Not, Null, Primary, Key (field name 1, field name 2), Field name 3 Field name N ) Alter table structure after build table: CREATE TABLE table name (field name 1, Int, Not, Null, Field name 2 nvarchar (13) Not Null Field name 3 Field name N ) GO ALTER TABLE table name WITH NOCHECK ADD CONSTRAINT [PK_ table name] PRIMARY KEY NONCLUSTERED ( [field name 1], [field name 2] ) GO [] 2. creates a primary key constraint using the SQL statement Creating a primary key constraint using the SQL statement can be created when you create a table (Create Table) or modify a table (Alter, Table). Creates a primary key constraint syntax in the modified table: ALTER TABLE table_name ADD CONSTR