SQL: CREATE TABLE Statement

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这篇内容介绍了如何使用SQL的CREATE TABLE语句创建表格，包括定义列的数据类型和约束，如NOT NULL和PRIMARY KEY。提供了两个实践练习，第一个是创建一个名为`customers`的表来存储客户信息，其中customer_id是主键；第二个练习涉及创建`employees`表，包含员工信息，并设置employee_number为主键，同时创建了一个外键引用`departments`表的department_id。

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The SQL CREATE TABLE statement allows you to create and define a table.

The syntax for the SQL CREATE TABLE statement is:

CREATE TABLE table_name

  column1 datatype null/not null,

  column2 datatype null/not null,

...

);

Each column must have a datatype. The column should either be defined as "null" or "not null" and if this value is left blank, the database assumes "null" as the default.

For Example

CREATE TABLE suppliers

( supplier_id number(10) not null,

  supplier_name varchar2(50) not null,

  contact_name varchar2(50)

);

Practice Exercise #1:

Create an SQL table called customers that stores customer ID, name, and address information. The customer ID should be the primary key for the table.

Solution:

The SQL CREATE TABLE statement for the customers table is:

CREATE TABLE customers

( customer_id number(10) not null,

  customer_name varchar2(50) not null,

  address varchar2(50),

  city varchar2(50),

  state varchar2(25),

  zip_code varchar2(10),

  CONSTRAINT customers_pk PRIMARY KEY (customer_id)

);

Practice Exercise #2:

Based on the departments table below, create an SQL table called employees that stores employee number, employee name, department, and salary information. The primary keyfor the employees table should be the employee number. Create a foreign key on the employees table that references the departments table based on the department_id field.

CREATE TABLE departments

( department_id number(10) not null,

  department_name varchar2(50) not null,

  CONSTRAINT departments_pk PRIMARY KEY (department_id)

);

Solution:

The SQL CREATE TABLE statement for the employees table is:

CREATE TABLE employees

( employee_number number(10) not null,

  employee_name varchar2(50) not null,

  department_id number(10),

  salary number(6),

  CONSTRAINT employees_pk PRIMARY KEY (employee_number),

  CONSTRAINT fk_departments

    FOREIGN KEY (department_id)

    REFERENCES departments(department_id)

);