Does SQL Server's `WHERE` Clause Ignore Trailing Spaces in String Comparisons?

SQL WHERE Clause: Trailing Spaces in Value Matching

In SQL Server, string comparisons using the WHERE clause exhibit a peculiar behavior that can lead to unexpected results. Specifically, the equality operator (=) ignores trailing spaces when performing comparisons.

Consider the following scenario:

• A table named Zone exists with a primary key column called ZoneReference of type varchar(50) with the NOT NULL constraint.
• A query is executed to select the QuotedZoneReference value for a ZoneReference value of 'WF11XU':

select '"' + ZoneReference + '"' as QuotedZoneReference
from Zone
where ZoneReference = 'WF11XU'

Surprisingly, the query returns the following result:

"WF11XU "

Explanation:

This behavior stems from the SQL-92 specification, which dictates that strings in comparison operations should be padded with spaces to ensure they have the same length before the comparison. In this case, the ZoneReference value in the WHERE clause ('WF11XU') is padded with a trailing space, resulting in a match with the value in the table.

Implications:

This padding can lead to issues when attempting to match exact values that may contain trailing spaces. For example, if the intended ZoneReference value was actually 'WF11XU' without the trailing space, the query would return no results.

Solutions:

To ensure accurate matches, consider the following solutions:

• Use the TRIM() function to remove trailing spaces from both the WHERE clause value and the table column value.
• Explicitly cast the strings to a data type that doesn't allow trailing spaces, such as nvarchar(50).
• Adjust the SQL Server collation settings to be case-sensitive and space-sensitive, which will prevent trailing spaces from being ignored.

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