mysql>createtabledepartment4(idint,namevarchar(16),constraintprimarykey(name)); Query OK,0rows affected (0.01sec) mysql>descdepartment4;+-------+-------------+------+-----+---------+-------+|Field|Type|Null|Key|
MySQL PRIMARY KEY ConstraintThe PRIMARY KEY constraint uniquely identifies each record in a table.Primary keys must contain UNIQUE values, and cannot contain NULL values.A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields)...
(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,既建立了...
4 rows in set (0.14 sec) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 第二种方法:在定义完所有列之后,指定主键的语法格式为:[CONSTRAINT <约束名>] PRIMARY KEY [字段名] 示例2,在 demo_db 数据库中创建 demo_employee 4 数据表,其主键为 id,测试SQL语句...
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 下面是一个在persons表格里面,设定ID为主键的代码: MySQL: CREATE TABLE Persons ( ID int NOT NULL, ...
mysql> ALTER TABLE np_pk -> PARTITION BY HASH( TO_DAYS(added) ) -> PARTITIONS 4; ERROR 1503 (HY000): A PRIMARY KEY must include all columns in the table's partitioning function However, this statement using the id column for the partitioning column is valid, as shown here: ...
[CONSTRAINT <约束名>]PRIMARYKEY[字段名] 【实例 2】在 test_db 数据库中创建 tb_emp 4 数据表,其主键为 id,输入的 SQL 语句和运行结果如下所示。 mysql>CREATETABLEtb_emp4->(->idINT(11),->nameVARCHAR(25),->deptIdINT(11),->salaryFLOAT,->PRIMARYKEY(id)->); ...
4.3.2.14.3 columns The column(s) for the primary key Table 4.96 columns ParameterDescription return the column(s) for the primary key4.3.2.14.4 name Name of the primary key constraint Table 4.97 name ParameterDescription return the name of the primary key constraint...
constraint_name The name of the primary key. column1, column2, ... column_n The columns that make up the primary key. Example Let's look at an example of how to create a primary key using the CREATE TABLE statement in MySQL. CREATE TABLE contacts ( contact_id INT(11) NOT NULL AUTO...
Let us see how we to apply the PRIMARY key constraint:Suppose we are asked to create a table named "student_details" and inside this table, we have to make 6 columns named as, student_ID (this should be PRIMARY key as well as Auto incremented), student_name, student_department, year,...