T-SQL Deterministic INT Cast

Question

Given:

• SQL Server
• Table called TEST_TABLE
• Column in TEST_TABLE called TEST_FIELD of type VARCHAR(50) NOT NULL
• Row 1: 10YR3/6
• Row 2: 10YR3/2
• Query: SELECT TEST_FIELD FROM TEST_TABLE WHERE ...

Question:

In my where condition I need to test for values in the last character of the string. I notice the same behavior doing the following in the Where clause.

1. RIGHT(TEST_FIELD,1) > 3
2. CAST(RIGHT(TEST_FIELD,1) AS INT) > 3

Are they behaving the same through some inferred cast in case 1? Is case 1 deterministic?

Thanks in advance.

Matt

Answer 1

A conversion is done when you check the value for instance:

DECLARE @t varchar(100)

SET @t = (SELECT 'ABCA2')

SELECT @t    

IF RIGHT(@t, 2) > 10
  SELECT 'Hi'
ELSE
  SELECT 'Bye'

Will throw an error because SQL cannot convert A2 to an integer without throwing an error.

However if you replace @t with:

SET @t = (SELECT 'ABC12')

The above code will work as a conversion is successful and a comparison can be made. The right function itself does not convert your value. MSDN states the return type of RIGHT() explicitly:

Returns varchar when character_expression is a non-Unicode character data type.

Returns nvarchar when character_expression is a Unicode character data type.

To make it easier on yourself, eliminate the function RIGHT() altogether, when a comparison is done with text for instance:

DECLARE @t varchar(100)

SET @t = (SELECT '1')

SELECT @t

IF @t < 10
  SELECT 'Hi'
ELSE
  SELECT 'Bye'

Notice I did not make a call to Right(). The result of the above is the display of 1 and then of the text Hi.

Answer 2

And Yes case 1 is deterministic - either successful implicit conversion from string to integer(end then comparison between two integers) or exception thrown.