Back in March 2025 when Microsoft first announced that REGEX support was coming to SQL Server 2025 and Azure SQL DB, I gave it a quick test, and the performance was horrific. It was bad in 3 different ways:
- The CPU usage was terrible, burning 60 seconds of CPU time to check a few million rows
- It refused to use an index
- The cardinality estimation was terrible, hard-coded to 30% of the table
Read on to see what has changed. It’s obviously not perfect, but just as obviously is much better than what Brent saw in Azure SQL DB at the time.