How to handle NULL values in T-SQL JOIN conditions without losing performance?
I'm prototyping a solution and I'm a bit lost with This might be a silly question, but I'm currently working with a scenario with an inner join between two tables in SQL Server 2019 where some key columns contain NULL values... The join condition looks something like this: ```sql SELECT a.*, b.* FROM TableA a INNER JOIN TableB b ON a.KeyColumn = b.KeyColumn WHERE a.Status = 'Active'; ``` The question arises when `KeyColumn` in either `TableA` or `TableB` has NULL values. I want to only join the rows where both `KeyColumn` values are not NULL, but when I run the query, it returns fewer rows than expected. I tried modifying the join condition to include a check for NULL values: ```sql SELECT a.*, b.* FROM TableA a INNER JOIN TableB b ON a.KeyColumn = b.KeyColumn AND a.KeyColumn IS NOT NULL AND b.KeyColumn IS NOT NULL WHERE a.Status = 'Active'; ``` However, this seems to have caused a performance drop. The execution plan indicates more costly operations than before. I also considered using a LEFT JOIN and filtering the results afterward, but I fear that may lead to even worse performance as the datasets are quite large (over 1 million rows each). Is there an optimal way to handle this scenario while ensuring that performance remains acceptable? Any advice on indexing strategies or alternative join conditions would be greatly appreciated. This is part of a larger application I'm building. Am I missing something obvious? I'm using Sql 3.9 in this project. My team is using Sql for this desktop app. Could someone point me to the right documentation?