Home > ETL Best Practices > SET IDENTITY_INSERT

SET IDENTITY_INSERT

During ETL process, if we are allowed to directly using SQL insert (rather than vendor’s own ETL tool, most of which does a great job in maintaining referential integrity, but short on performance), then we need to worry about the primaries keys and referential integrity. Most primary keys are system generated identity columns.

This SQL statement allows explicit values to be inserted into the identity column of a table.

Remarks

At any time, only one table in a session can have the IDENTITY_INSERT property set to ON. If a table already has this property set to ON, and a SET IDENTITY_INSERT ON statement is issued for another table, Microsoft® SQL Server™ returns an error message that states SET IDENTITY_INSERT is already ON and reports the table it is set ON for.

If the value inserted is larger than the current identity value for the table, SQL Server automatically uses the new inserted value as the current identity value.

The setting of SET IDENTITY_INSERT is set at execute or run time and not at parse time.

This example from MSDN creates a table with an identity column and shows how the SET IDENTITY_INSERT setting can be used to fill a gap in the identity values caused by a DELETE statement.

-- Create products table.
CREATE TABLE products (id int IDENTITY PRIMARY KEY, product varchar(40))
GO
-- Inserting values into products table.
INSERT INTO products (product) VALUES ('screwdriver')
INSERT INTO products (product) VALUES ('hammer')
INSERT INTO products (product) VALUES ('saw')
INSERT INTO products (product) VALUES ('shovel')
GO

-- Create a gap in the identity values.
DELETE products 
WHERE product = 'saw'
GO

SELECT * 
FROM products
GO

-- Attempt to insert an explicit ID value of 3;
-- should return a warning.
INSERT INTO products (id, product) VALUES(3, 'garden shovel')
GO
-- SET IDENTITY_INSERT to ON.
SET IDENTITY_INSERT products ON
GO

-- Attempt to insert an explicit ID value of 3
INSERT INTO products (id, product) VALUES(3, 'garden shovel').
GO

SELECT * 
FROM products
GO
-- Drop products table.
DROP TABLE products
GO
Categories: ETL Best Practices
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