Как добавить auto increment поле в существующую таблицу mysql
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MySQL 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.
MySQL AUTO_INCREMENT Keyword
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.
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:
When we insert a new record into the "Persons" table, we do NOT have to specify a value for the "Personid" column (a unique value will be added automatically):
The SQL statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned a unique value automatically. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".
How to Add Auto Increment Column in Existing Table in MySQL
Auto Increment columns automatically increase in value as you add more rows to the table. In this article we will look at how to add auto increment column in MySQL.
How to Add Auto Increment Column
Here are the steps to add auto increment column in MySQL. Let’s say you have the following sales(id, amount) table.
Now, we will modify the id column to be auto increment, using ALTER TABLE.
Here’s the syntax of ALTER TABLE statement,
In the above statement, you need to specify the table_name and column_name.
Here’s the SQL statement to add AUTO INCREMENT constraint to id column.
Next we will add a couple of rows in sales table.
As you can see, the MySQL has automatically increased and populated id column with values 7 and 8.
You can also add auto increment column during table creation. However, remember that auto increment constraint can be assigned only to primary key column.
Here’s the syntax to add auto increment column during table creation.
Here’s an example to add auto increment column in MySQL
As you can see above, the id column is automatically incremented and populated.
How to Set Auto Increment Initial Value
By default, auto increment column value starts from 1. You can change auto increment start value if you want. Here’s the syntax for it,
In the above SQL query, you need to specify the table_name as well as increment_value.
For example, here’s the SQL query to set initial increment value to 100
Hopefully, the above article will help you add auto increment column in existing table in MySQL.
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How to use Auto Increment in SQL?
Databases are known to store a humongous amount of data in a logical format. But, have you ever thought about a situation, wherein you have to mention a unique number for every new record in a table? Well, I think, it’s practically impossible to enter the numbers manually. So, instead, you can use Auto Increment in SQL, to automatically enter a unique number for every new record in the table.
The following topics will be covered in this article:
1)What is an auto-increment in SQL?
2)How do you set up Auto Increment?
- SQL Server
- MySQL
- MS Access
- Oracle
- PostgreSQL
What is an auto-increment in SQL?
I am sure the name suggests its functionality by itself. Auto Increment is a field used to generate a unique number for every new record added to a table. This is generally used for the primary key column as it becomes easy for the developers to automatically generate a unique number for every new record.
Now, that you know, what is an auto-increment in SQL, let us discuss how to use this field in various DBMS.
How do you set up Auto Increment?
For your better understanding, I will consider the following table:
Syntax and Example for SQL Server
To use the auto-increment field, in SQL Server, you have to use the IDENTITY keyword.
Syntax:
Example:
Create a table with the name Customers, and columns CustomerID, CustomerName, Age, and PhoneNumber. Here, auto-increment the CustomerID and make it the primary key for the table.
In the above example, the Also, to insert values in the above table, you have to use the starting value for IDENTITY is 1 and it should INSERT query in the following way: increment by 1 for every new record added. You can mention these values, according to your wish.
Here, if you observe, I have not mentioned the CustomerID column, as the ID will be automatically generated. So, if you see insert 4 more values using the below queries:
Then, you will see the below output:
Next, in this article on auto-increment in SQL, let us see how to auto-increment a column in MySQL.
Syntax and Example for MySQL
To use the auto-increment field, in MySQL, you have to use the AUTO_INCREMENT keyword. the starting value for AUTO_INCREMENT is 1 by default, and it will increment by 1 for each new record.
Syntax:
Example:
Create a table with the name Customers, and columns CustomerID, CustomerName, Age, and PhoneNumber. Here, auto-increment the CustomerID and make it the primary key for the table.
If you wish to start the AUTO_INCREMENT value by any other number, then you can use the keyword in the following way:
Syntax:
Example:
Similar to that of SQL Server, you can INSERT values into the table, by using the INSERT statement. On inserting values, you will see the same output, as that of the above table. Next, in this article on auto-increment in SQL, let us see how to auto-increment a column in MS Access.
Syntax and Example for MS Access
To use the auto-increment field, in MS Access, you have to use the AUTOINCREMENT keyword.
Syntax:
Example:
Create a table with the name Customers, and columns CustomerID, CustomerName, Age, and PhoneNumber. Here, auto-increment the CustomerID and make it the primary key for the table.
The default starting value of AUTOINCREMENT is 1 and it will also increment by 1 for each record. But, if you wish to change this, and let us say, you want to set the starting value to be 20 and increment by 2, you can use the auto-increment feature as below:
Similar to that of SQL Server, you can INSERT values into the table, by using the INSERT statement. On inserting values, you will see the same output, as that of the above table. Next, in this article on auto-increment in SQL, let us see how to auto-increment a column in Oracle.
Syntax and Example for Oracle
To use the auto-increment field, in Oracle, you have to create an auto-increment field with the sequence object. The sequence object generates a number sequence.
Syntax to create a sequence:
In the above syntax,
- Name_of_sequence — Creation of sequence named name_of_sequence
- START — Mentions the starting value
- INCREMENT BY — Mentions the value incremented by
- CACHE — Mentions the maximum number of values to be stored for faster access.
Example:
Create a sequence object where the starting value is 1, is incremented by 3, and a maximum number of values to be stored is 20.
Similar to that of MySQL and SQL Server, you can INSERT values into the table, by using the INSERT statement. On inserting values, you will see the same output, as that of the above table. Next, in this article on auto-increment in SQL, let us see how to auto-increment a column in PostgreSQL.
Syntax and Example for PostgreSQL
To use the auto-increment field, in PostgreSQL, you have to create an auto-increment field with the sequence object. The sequence object generates a number sequence.
Syntax:
Example:
Create a table with the name Customers, and columns CustomerID, CustomerName, Age and PhoneNumber. Here, auto-increment the CustomerID and make it the primary key for the table.
Similar to that of MySQL, SQL Server, and other DBMS you can INSERT values into the table, by using the INSERT statement. On inserting values, you will see the same output, as that of the above table. I hope you guys enjoyed this article and understood all the differences. If you wish to check out more articles on the market’s most trending technologies like Artificial Intelligence, DevOps, Ethical Hacking, then you can refer to Edureka’s official site.
Do look out for other articles in this series which will explain the various other aspects of SQL.