Data type precedence - SQL Server

     In SQL Server, data type precedence determines which data type takes precedence over others when two or more data types are combined or compared. It is important to understand data type precedence to ensure that the correct data type is used and that data is not lost or truncated during operations. In this blog, we will discuss data type precedence in SQL Server with examples.

Data type precedence levels

SQL Server has 16 data type precedence levels, with the highest level being 1 and the lowest level being 16. The data type with the lowest precedence is considered to be the "weakest" data type and is most likely to be converted to a higher precedence data type during operations. Here is the list of data types in SQL Server, ordered by their precedence levels:

user-defined data types (highest precedence)

sql_variant

xml

datetimeoffset

datetime2

datetime

smalldatetime

date

time

float

real

decimal/numeric

money/smallmoney

bigint/int

smallint

tinyint/bit (lowest precedence)

Data type precedence examples

Let's take a look at some examples of data type precedence in SQL Server:

Example 1:

DECLARE @result numeric(10,2)

SET @result = 10 / 3

SELECT @result

 

In this example, we are declaring a numeric variable with precision 10 and scale 2. We then set the value of the variable to the result of dividing 10 by 3. Since the result of the division is a decimal number, SQL Server will convert the result to the highest precedence data type in the expression, which is numeric. The output of this query will be 3.33.

Example 2:

DECLARE @value varchar(10)

SET @value = '123'

SELECT @value + 5

 

In this example, we are declaring a varchar variable and setting its value to '123'. We then try to add the value of the variable to the integer value 5. Since the data types of the operands are different, SQL Server will try to convert the varchar value to an integer. However, since varchar has a lower precedence than integer, the value of @value will be truncated to '12'. The output of this query will be 17.

Example 3:

DECLARE @date datetime

SET @date = '2022-03-21'

SELECT @date + 1

 In this example, we are declaring a datetime variable and setting its value to '2022-03-21'. We then try to add the value of the variable to the integer value 1. Since datetime has a higher precedence than integer, SQL Server will convert the integer value to a datetime value by adding one day to the date value. The output of this query will be '2022-03-22 00:00:00.000'.

Conclusion

In SQL Server, data type precedence determines which data type takes precedence over others during operations. It is important to understand data type precedence to ensure that the correct data type is used and that data is not lost or truncated during operations. By using the appropriate data types and being aware of data type precedence, we can ensure that our SQL Server queries and procedures are accurate, efficient, and reliable.

Reference

              https://learn.microsoft.com/en-us/sql/t-sql/data-types/data-type-precedence-transact-sql?view=sql-server-ver16