The syntax to create a primary key using the ALTER TABLE statement in SQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n); table_name The name of the table to modify. This is the table that you wish to add a primary key to. ...
PRIMARY KEYPRIMARY KEY 约束唯一地标识表中的每条记录。 一个表只能有一个主键,它可以由一个或多个字段组成。建表时创建 PRIMARY KEY 约束 下面的 SQL 在 "Persons" 表创建时在 "ID" 列创建 PRIMARY KEY 约束:MySQL:CREATE TABLE Persons( ID int NOT NULL, LastName varchar(255) NOT NULL, FirstName ...
SQL Másolás ALTER TABLE Production.TransactionHistoryArchive ADD CONSTRAINT PK_TransactionHistoryArchive_TransactionID PRIMARY KEY CLUSTERED (TransactionID); Create a primary key in a new tableThe following example creates a table and defines a primary key on the column TransactionID in the ...
(1)在字段级以key方式建立, 如 create table t (id int not null primary key); (2)在表级以constraint方式建立,如 create table t(id int, CONSTRAINT pk_t_id PRIMARY key (id)); (3)在表级以key方式建立,如 create table t(id int, primary key (id)); 其它key创建类似,但不管那种方式,既建...
如果"sql_require_primary_key"设置为ON,意思就是表任何的时刻都需要有主键,不能出现真空。变更主键的操作,实际包含了删除原主键和创建新的主键两个步骤,因此只需要将两个步骤合并成一个即可。 MySQL支持多个语句一次执行,因此只需要将alter table ... ...
For a relational database like PostgreSQL, it could widely be considered a sin among developers not to include a primary key in every table. It is therefore crucial that you do your utmost to add that all-important primary key column to every table, and thankfully Postgres provides two metho...
修改数据表tb_emp2,将字段id设置为主键,SQL语句如下: mysql>altertabletb_emp2addprimarykey(id); Query OK,0rowsaffected (0.02sec) Records:0Duplicates:0Warnings:0mysql>desctb_emp2;+---+---+---+---+---+---+|Field|Type|Null|Key|Default|Extra|+---+---+---+---+---+---+|id...
To create a non clustered primary key on an existing table:[cc lang=”sql”] ALTER TABLE dbo.Person ADD CONSTRAINT PK_Person PRIMARY KEY NONCLUSTERED (PersonID); [/cc]To create a composite primary key on an existing table:[cc lang=”sql”] ALTER TABLE dbo.Person ADD CONSTRAINT PK_...
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 ...
1.语法:ALTER TABLE 表名 ADD CONSTRAINT 主键名 PRIMARY KEY 表名(主键字段); 3.添加外键 1.语法:ALTER TABLE 表名 ADD CONNSTRAINT 外键名 FOREIGN KEY(外键字段) REFERENCES 关联表名(关联字段); 4.插入单(多)条数据记录(和SQL Server相同,但是不能用select多列添加数据) ...