- Introduction To SQL
- SQL Syntax
- SQL SELECT Statement
- SQL SELECT DISTINCT Statement
- SQL WHERE Clause
- SQL AND, OR And NOT Operators
- SQL ORDER BY Keyword
- SQL INSERT INTO Statement
- SQL NULL Values
- SQL UPDATE Statement
- SQL DELETE Statement
- SQL TOP, LIMIT, FETCH FIRST Or ROWNUM Clause
- SQL MIN() And MAX() Functions
- SQL COUNT(), AVG() And SUM() Functions
- SQL LIKE Operator
- SQL Wildcards
- SQL IN Operator
- SQL BETWEEN Operator
- SQL Aliases
- SQL Joins
- SQL INNER JOIN Keyword
- SQL LEFT JOIN Keyword
- SQL RIGHT JOIN Keyword
- SQL FULL OUTER JOIN Keyword
- SQL Self Join
- SQL UNION Operator
- SQL GROUP BY Statement
- SQL HAVING Clause
- SQL EXISTS Operator
- SQL ANY And ALL Operators
- SQL SELECT INTO Statement
- SQL INSERT INTO SELECT Statement
- SQL CASE Statement
- SQL NULL Functions
- SQL Stored Procedures For SQL Server
- SQL Comments
- SQL Operators
- SQL CREATE DATABASE Statement
- SQL DROP DATABASE Statement
- SQL BACKUP DATABASE For SQL Server
- SQL CREATE TABLE Statement
- SQL DROP TABLE Statement
- SQL ALTER TABLE Statement
- SQL Constraints
- SQL NOT NULL Constraint
- SQL UNIQUE Constraint
- SQL PRIMARY KEY Constraint
- SQL FOREIGN KEY Constraint
- ALTER TABLE Orders DROP CONSTRAINT FK_PersonOrder;
- SQL DEFAULT Constraint
- SQL CREATE INDEX Statement
- SQL AUTO INCREMENT Field
- SQL Working With Dates
- SQL Views
- SQL Injection
- SQL Hosting
- SQL Data Types For MySQL, SQL Server, And MS Access
SQL AUTO INCREMENT Field
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.
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Syntax For MySQL
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
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):
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".
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Syntax For SQL Server
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
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.
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):
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".
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Syntax For Access
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
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):
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".
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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).
Use the following CREATE SEQUENCE syntax:
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10;
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):
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".
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