This SQL tutorial explains how to use the SQL CREATE TABLE statement with syntax, examples, and practice exercises.
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Description
The first is PRIMARY KEY, which as the name suggests, forces the specified column to behave as a completely unique index for the table, allowing for rapid searching and queries. While SQL Server only allows one PRIMARY KEY constraint assigned to a single. CREATE TABLE books (id INT NOT NULL IDENTITY PRIMARY KEY, title VARCHAR (100) NOT NULL, primaryauthor VARCHAR (100),); That’s all there is to it. Now the id column of our books table will be automatically incremented upon every INSERT and the id field is guaranteed to be a unique value as well.
The SQL CREATE TABLE statement allows you to create and define a table.
Syntax
The syntax for the CREATE TABLE statement in SQL is:
Parameters or Arguments
- table_name
- The name of the table that you wish to create.
- column1, column2
- The columns that you wish to create in the table. 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.
Example
Let's look at a SQL CREATE TABLE example.
This SQL CREATE TABLE example creates a table called suppliers which has 3 columns.
- The first column is called supplier_id which is created as a number datatype (maximum 10 digits in length) and can not contain null values.
- The second column is called supplier_name which is a char datatype (50 maximum characters in length) and also can not contain null values.
- The third column is called contact_name which is a char datatype but can contain null values.
Now the only problem with this SQL CREATE TABLE statement is that you have not defined a primary key for the table. We could modify this SQL CREATE TABLE statement and define the supplier_id as the primary key as follows:
Learn about primary keys.
Learn about foreign keys.
Practice Exercise #1:
Create a SQL table called customers that stores customer ID, name, and address information.
Solution for Practice Exercise #1:
The SQL CREATE TABLE statement for the customers table is:
Practice Exercise #2:
Create a SQL table called customers that stores customer ID, name, and address information.
But this time, the customer ID should be the primary key for the table.
Solution for Practice Exercise #2:
![Generate Primary Key When Creating A Table Sql Generate Primary Key When Creating A Table Sql](/uploads/1/2/6/1/126131775/231726934.jpg)
The SQL CREATE TABLE statement for the customers table is:
Practice Exercise #3:
Based on the departments table below, create a SQL table called employees that stores employee number, employee name, department, and salary information. The primary key for 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.
Solution for Practice Exercise #3:
The SQL CREATE TABLE statement for the employees table is:
AUTO INCREMENT Field
Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table.
Often this is the primary key field that we would like to be created automatically every time a new record is inserted.
Syntax for MySQL
The following SQL statement defines the 'Personid' column to be an auto-increment primary key field in the 'Persons' table:
CREATE TABLE Persons (
Personid int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (Personid)
);
Personid int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (Personid)
);
MySQL uses the AUTO_INCREMENT keyword to perform an auto-increment feature.
By default, the starting value for AUTO_INCREMENT is 1, and it will increment by 1 for each new record.
To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:
To insert a new record into the 'Persons' table, we will NOT have to specify a value for the 'Personid' column (a unique value will be added automatically):
INSERT INTO Persons (FirstName,LastName)
VALUES ('Lars','Monsen');
VALUES ('Lars','Monsen');
The SQL statement above would insert a new record into the 'Persons' table. The 'Personid' column would be assigned a unique value. The 'FirstName' column would be set to 'Lars' and the 'LastName' column would be set to 'Monsen'.
Syntax for SQL Server
The following SQL statement defines the 'Personid' column to be an auto-increment primary key field in the 'Persons' table:
CREATE TABLE Persons (
Personid int IDENTITY(1,1) PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
Personid int IDENTITY(1,1) PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
The MS SQL Server uses the IDENTITY keyword to perform an auto-increment feature.
In the example above, the starting value for IDENTITY is 1, and it will increment by 1 for each new record.
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Tip: To specify that the 'Personid' column should start at value 10 and increment by 5, change it to IDENTITY(10,5).
To insert a new record into the 'Persons' table, we will NOT have to specify a value for the 'Personid' column (a unique value will be added automatically):
INSERT INTO Persons (FirstName,LastName)
VALUES ('Lars','Monsen');
VALUES ('Lars','Monsen');
The SQL statement above would insert a new record into the 'Persons' table. The 'Personid' column would be assigned a unique value. The 'FirstName' column would be set to 'Lars' and the 'LastName' column would be set to 'Monsen'.
Syntax for Access
The following SQL statement defines the 'Personid' column to be an auto-increment primary key field in the 'Persons' table:
CREATE TABLE Persons (
Personid AUTOINCREMENT PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
Personid AUTOINCREMENT PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
The MS Access uses the AUTOINCREMENT keyword to perform an auto-increment feature.
By default, the starting value for AUTOINCREMENT is 1, and it will increment by 1 for each new record.
Tip: To specify that the 'Personid' column should start at value 10 and increment by 5, change the autoincrement to AUTOINCREMENT(10,5).
To insert a new record into the 'Persons' table, we will NOT have to specify a value for the 'Personid' column (a unique value will be added automatically):
![Generate Generate](/uploads/1/2/6/1/126131775/794729734.gif)
INSERT INTO Persons (FirstName,LastName)
VALUES ('Lars','Monsen');
VALUES ('Lars','Monsen');
The SQL statement above would insert a new record into the 'Persons' table. The 'Personid' column would be assigned a unique value. The 'FirstName' column would be set to 'Lars' and the 'LastName' column would be set to 'Monsen'.
Syntax for Oracle
In Oracle the code is a little bit more tricky.
You will have to create an auto-increment field with the sequence object (this object generates a number sequence).
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Use the following CREATE SEQUENCE syntax:
CREATE SEQUENCE seq_person
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10;
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10;
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The code above creates a sequence object called seq_person, that starts with 1 and will increment by 1. It will also cache up to 10 values for performance. The cache option specifies how many sequence values will be stored in memory for faster access.
To insert a new record into the 'Persons' table, we will have to use the nextval function (this function retrieves the next value from seq_person sequence):
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INSERT INTO Persons (Personid,FirstName,LastName)
VALUES (seq_person.nextval,'Lars','Monsen');
VALUES (seq_person.nextval,'Lars','Monsen');
The SQL statement above would insert a new record into the 'Persons' table. The 'Personid' column would be assigned the next number from the seq_person sequence. The 'FirstName' column would be set to 'Lars' and the 'LastName' column would be set to 'Monsen'.