既然"sql_require_primary_key"参数控制了强制检验主键,而且又是可动态修改的,临时关闭,再打开即可, bisal@mysqldb: [test]> alter table t_primary_key drop primary key; ERROR 3750 (HY000): Unable to create or change a table without a primary key, when the system variable 'sql_require_primary_key...
参数名称:sql_require_primary_key作用范围:Global & Session动态修改:Yes默认值:OFF该参数设置为ON时,SQL语句create table创建新表或者alter语句对已存在的表进行修改,将会强制检查表中是否包含主键,如果没有主键,则会报错。 针对这个场景,是否还可以将主...
To create a primary key column, you can use the graphical user interface (GUI) of SQL Server Management Studio by following these steps. 1. Start by opening your database, then find and right-click on the table where you plan to add the primary key. 2. Then, right-click on the colum...
Let's look at an example of how to drop a primary key using the ALTER TABLE statement in SQL. ALTER TABLE suppliers DROP PRIMARY KEY; In this example, we've dropped the primary key on thesupplierstable. We do not need to specify the name of the primary key as there can only be one...
SQL PRIMARY KEY Constraint SQL 主键约束 主键包含的都是Unique 不重复,Not NULL 不为空的数据。 The PRIMARY KEY constraint uniquely identifies each record in a table. 一个表格只能有一个主键,逐渐可以包含一个或者多个列。 SQL PRIMARY KEY on CREATE TABLE ...
Create a primary key in a new tableThe following example creates a table and defines a primary key on the column TransactionID in the AdventureWorks database.SQL Másolás CREATE TABLE Production.TransactionHistoryArchive1 ( TransactionID int IDENTITY (1,1) NOT NULL , CONSTRAINT PK_Transaction...
Primary key Constraints和unique Constraints都需要保证列是唯一的,不能有重复值,但是一张表只能有一个Primary key Constraints,但是可以有多个unique Constraints。 主键约束比唯一索引约束严格,当没有设定主键时,非空唯一索引自动称为主键。对于主键和唯一索引的一些区别主要如下: ...
SELECT s4.name,s3.keyno FROM sys.sysobjects s INNER JOIN sys.sysindexes s2 ON s.id = s2.id AND (s2.status=2066 OR s2.status = 2050) INNER JOIN sys.sysindexkeys s3 ON s2.id = s3.id AND s2.indid = s3.indid INNER JOIN sys.syscolumns s4 ON s3.id = s4.id AND s3.colid = s4...
SQL PRIMARY KEY 约束 PRIMARY KEY 约束唯一标识数据库表中的每条记录。主键必须包含唯一的值。主键列不能包含 NULL 值。每个表都应该有一个主键，并且每个表只能有一个主键。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:CREATE ...
primarykey_name - Represents the user defined name of the primary key. column1, column2, column3 - Represents the name of the columns which include in table. column_name - Represents the name of the column on which we going to create primary key. table_name –Represents the name of ...