SA0058 : Avoid converting dates to string during date comparison

Comparing dates by converting them to strings can lead to inefficient queries, as it prevents the use of indexes and introduces potential errors due to format mismatches.

Description

Comparing dates through conversion to string using the CONVERT function can lead to inefficient queries and unexpected results. This approach is problematic because it bypasses the optimized date handling capabilities of SQL Server, which may result in performance degradation and incorrect comparisons.

For example:

SQL
Copy
1-- Example of problematic query
2SELECT *
3FROM Orders
4WHERE CONVERT(VARCHAR, OrderDate, 101) = '12/31/2020';

In this example, the OrderDate column is converted to a string before comparison, which can lead to a full table scan and is susceptible to format mismatches. Direct date comparisons without conversion are preferred to improve query efficiency and accuracy.

  • Performance impact: Using string conversion can prevent the query optimizer from using indexes effectively, leading to slower query execution.

  • Potential inaccuracies: Different date formats and language settings can cause errors or unexpected results in comparisons.

How to fix

Optimize date comparisons by avoiding string conversions and using native date functions like DATEADD and DATEDIFF for efficiency and accuracy.

Follow these steps to address the issue:

  1. Analyze the original query to identify any use of CONVERT function for date comparisons, which can lead to inefficient execution plans.

  2. Replace the conversion and string comparison with a direct date comparison. Ensure that both sides of the comparison are datetime data types.

  3. If necessary, utilize functions like DATEADD and DATEDIFF to manipulate and compare date values directly in their native format.

For example:

SQL
Copy
1-- Example of corrected query
2SELECT *
3FROM Orders
4WHERE OrderDate = '2020-12-31';

Scope

The rule has a Batch scope and is applied only on the SQL script.

Parameters
Name Description Default Value
MatchInWhereAndJoinOnly

Match the date conversions only in WHERE or JOIN clauses.

yes
Remarks

The rule requires Analysis Context. If context is missing, the rule will be skipped during analysis.

Effort To Fix
20 minutes per issue.
Categories

Design Rules, Bugs

Additional Information

There is no additional info for this rule.

Example Test SQL
SQL
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1DECLARE  @date2 AS DATETIME = GETDATE()
2
3SELECT CONVERT( VARCHAR( 20 ), StartDate, 103 ) AS StartDate
4FROM  vEmployeeDepartment
5WHERE  CONVERT( VARCHAR( 20 ), @date2, 103 ) <= CONVERT( VARCHAR( 20 ), StartDate, 103 )
6
7UPDATE vEmployeeDepartment SET  StartDate = DATEADD( d, 1, StartDate )
8WHERE  CONVERT( VARCHAR( 20 ), @date2, 103 ) <= '2010-03-13 00:00:12.000'
Analysis Results
  Message Line Column
1 SA0058 : Avoid converting dates to string during date comparison. 5 7
2 SA0058 : Avoid converting dates to string during date comparison. 5 48
3 SA0058 : Avoid converting dates to string during date comparison. 8 7
See Also

Other Resources

Analysis Rules