Exploring SQL Server Identity Insert for Dev

Welcome, Dev! Are you a SQL Server developer looking to learn more about using Identity Insert in SQL Server? Look no further! This article will guide you through everything you need to know about SQL Server Identity Insert, including what it is, how to use it, and common FAQs.

What is SQL Server Identity Insert?

SQL Server Identity Insert is a feature that allows you to insert explicit values into the Identity column of a table. The Identity column is a special column that automatically generates unique integer values for new rows added to the table. By default, the Identity column starts at 1 and increments by 1 for each new row.

However, there may be cases where you need to insert a specific value into the Identity column, rather than allowing SQL Server to generate its own value. This is where Identity Insert comes in handy.

How does SQL Server Identity Insert work?

To use SQL Server Identity Insert, you must first ensure that your table has an Identity column. This column must be set up with the “Identity” property, which will automatically generate new unique values for each new row added to the table. You can then use the “Set Identity_Insert” command to turn on Identity Insert for that table. Once Identity Insert is turned on, you can manually insert values into the Identity column, either by specifying the value directly or by using a subquery to retrieve the value.

After the values have been inserted, you must turn Identity Insert off again using the “Set Identity_Insert” command. This will prevent any future inserts from manually assigning values to the Identity column.

When should you use SQL Server Identity Insert?

There are a few common scenarios where SQL Server Identity Insert may be necessary:

• Migrating data from another system that used different Identity values
• Importing data from external sources where Identity values must be preserved
• Manually reordering Identity values for better performance or organization

Keep in mind that using Identity Insert can be risky, especially if you manually assign values that conflict with existing values in the table. It’s important to use caution and carefully plan your use of Identity Insert to avoid data inconsistencies and errors.

How to Use SQL Server Identity Insert

Step 1: Ensure Your Table Has an Identity Column

Before you can use SQL Server Identity Insert, you need to make sure that your table has an Identity column. This column should be set up with the “Identity” property to ensure that new rows are automatically assigned unique values.

To create a new table with an Identity column, you can use the following syntax:

CREATE TABLE MyTable (ID int PRIMARY KEY IDENTITY(1,1),Name varchar(50) NOT NULL,Age int NOT NULL)

This will create a new table called MyTable with an Identity column called “ID”. The ID column will start at 1 and increment by 1 for each new row added to the table.

Step 2: Turn on Identity Insert for Your Table

Once you have an Identity column in your table, you can use the “Set Identity_Insert” command to turn on Identity Insert:

SET Identity_Insert MyTable ON

This will allow you to manually insert values into the Identity column for the MyTable table.

Step 3: Insert Values into the Identity Column

With Identity Insert turned on, you can now manually insert values into the Identity column. You can do this by specifying the value directly, like this:

INSERT INTO MyTable (ID, Name, Age)VALUES (100, 'John', 35)

This will insert a new row into MyTable with an ID of 100, a Name of “John”, and an Age of 35. Note that you must specify the ID value in the INSERT statement when using Identity Insert.

You can also use a subquery to retrieve the value to insert, like this:

INSERT INTO MyTable (ID, Name, Age)SELECT MAX(ID) + 1, 'Jane', 30FROM MyTable

This will insert a new row into MyTable with an ID value that is one greater than the maximum ID value currently in the table, a Name of “Jane”, and an Age of 30.

Step 4: Turn off Identity Insert

After you have finished inserting values into the Identity column, you should turn off Identity Insert to prevent future inserts from manually assigning values to the Identity column:

SET Identity_Insert MyTable OFF

This will restore the default behavior of automatically generating values for the Identity column for new rows.

FAQ

What happens if I insert a value that conflicts with an existing Identity value?

If you insert a value into the Identity column that conflicts with an existing value, you will receive an error message and the insert will fail. Make sure to avoid conflicts by carefully planning your use of Identity Insert.

Can I use Identity Insert on tables with foreign key constraints?

Yes, but you must be careful to ensure that the manually inserted values do not conflict with existing values in the related tables. It’s generally best to avoid using Identity Insert on tables with foreign key constraints unless absolutely necessary.

Can I specify the starting value for an Identity column?

Yes, you can specify the starting value for an Identity column using the “IDENTITY” property when creating the table. For example:

CREATE TABLE MyTable (ID int PRIMARY KEY IDENTITY(100,1),Name varchar(50) NOT NULL,Age int NOT NULL)

This will create a new table called MyTable with an Identity column called “ID” that starts at 100 and increments by 1 for each new row added to the table.

Can I use Identity Insert with a view?

No, Identity Insert can only be used with tables, not views.

What happens if I turn on Identity Insert for a table with no Identity column?

If you turn on Identity Insert for a table with no Identity column, you will receive an error message and the insert will fail.

Can I use Identity Insert in a transaction?

Yes, you can use Identity Insert in a transaction. However, keep in mind that any Identity values that are manually inserted will not be rolled back if the transaction is rolled back. This can result in gaps or conflicts in the Identity values.

That’s it, Dev! You now have a thorough understanding of SQL Server Identity Insert and how to use it in your development projects. Remember to use caution and plan carefully when using Identity Insert to avoid data inconsistencies and errors.