While creating Stored Procedures, User Defined Functions etc, most of us use the SET QUOTED_IDENTIFIER ON/OFF  and SET ANSI_NULLS ON/OFF. In this article will discuss on the SET QUOTED_IDENTIFIER ON/OFF Setting.

Depending on the QUOTED_IDENTIFIER setting value either ON or OFF, SQL Server treats the data defined within double quotes or single quotes as differently. If this setting value is ON, then SQL Server treats the value defined within double quotation marks as identifier. The T-SQL rules for the identifier will not apply for these double quoted identifiers, even we can use T-SQL reserved keywords as identifier. So we can use these double quoted identifiers as Stored Procedure name, table name, user defined function name, table name, column names etc.

Let us understand this with an example:

SET QUOTED_IDENTIFIER ON GO
CREATE TABLE dbo."Table"(id int,"Function" VARCHAR(20))
GO
INSERT  INTO dbo."Table" (id,"Function") VALUES (1,'Basavaraj')
GO
SELECT id,"Function" FROM dbo."Table" GO

Result of running the above query is as below:

id          Function
----------- --------------------
1           Basavaraj
(1 row(s) affected)

In the above example we are able to use the T-SQL reserve Keywords “Table” and “Function” as the Table Name and Column Name respectively.

When this setting is ON the data/characters enclosed within single quotation mark is treated as literal. We can’t use the double quoted characters or data as literal. Below example demonstrates this behaviour, in this example the first select statement succeeds where as second select statement fails because it treats the characters enclosed within double quotation mark as identifier.

SET QUOTED_IDENTIFIER ON
 GO
 SELECT 'BASAVARAJ'
 GO
 SELECT "BIRADAR"

Result of running above statement is as below:

---------
BASAVARAJ
(1 row(s) affected)
Msg 207, Level 16, State 1, Line 1 Invalid column name 'BIRADAR'.

On the other hand if SET QUOTED_IDENTIFIER setting is OFF, then SQL Server treats the values defined within single/double quotation mark as literal. Let us understand this with below two simple examples:

Example 1) This example demonstrates that, we can’t use double quoted identifiers when SET QUOTED_IDENTIFIER setting is OFF.

SET QUOTED_IDENTIFIER OFF GO
CREATE TABLE dbo."Table"(id int,"Function" VARCHAR(20))
GO

Result of running the above sql statements:

Msg 102, Level 15, State 1, Line 1 Incorrect syntax near 'Table'.

Example 2) This example demonstrates the fact that the values enclosed within either singles or double quotes is treated as literal when SET QUOTED_IDENTIFIER setting is OFF.

SET QUOTED_IDENTIFIER OFF GO
SELECT 'BASAVARAJ' GO
SELECT "BIRADAR"

Result of running the above statement is:

---------
BASAVARAJ
(1 row(s) affected)
-------
BIRADAR
(1 row(s) affected)

Another important point to note is that, the QUOTED_IDENTIFIER setting with which we create Stored Procedur will be stored in the meta data. So, whenever Stored Procedure executes, it will use these setting stored in the meta data. It will ignore the settings of the client or the calling application.

Below query can be used to find the objects which are created with SET QUOTED_IDENTIFIER setting as OFF.

SELECT OBJECT_NAME (object_id) FROM sys.sql_modules
WHERE uses_quoted_identifier = 0 -- 0 means OFF and 1 means ON

You would also like to read the article: Difference Between SET QUOTED_IDENTIFIERS ON and OFF settings.

Please correct me, if my understanding is wrong. Comments are always welcome.