To find the oldest statistics in SQL Server, read the last update time and the number of changes since. This post builds a small demo, lists every statistic with its age and percent changed, and shows why a high change count on its own is not a reason to update by hand.
Performance Regression After a SQL Server Upgrade: First Aid
A performance regression after an upgrade hurts most when users are waiting. This post shows a first-aid switch that brings back the old row estimates without lowering the compatibility level, and proves with a demo what changes and what stays. It also covers the undo, the per-query options and the steps that find the real cause.
Partition Switch in SQL Server: Move a Million Rows in a Moment
A partition switch moves a whole partition from one table to another without copying a single row. This post builds a partitioned table with a million rows, switches the January partition out and back in, and shows that only metadata changes. It lists the five errors that stop a switch, with the real message numbers, and ends with the sliding window pattern.
BETWEEN vs IN in SQL Server: Which One Reads Less?
BETWEEN vs IN looks like a style choice, and it is not. This post builds a demo table and measures BETWEEN, the two operators and an IN list with and without an index. It shows that BETWEEN and the operators share one plan, that IN seeks once for every value and that sparse values change the question.
SQL SERVER – Delete Statement and Index Usage
An index can help a DELETE statement locate rows to remove. A customer asked whether indexes benefit modifications alongside SELECT queries.
Statistics That Never Auto Update: Find the NORECOMPUTE Flag
Statistics that never auto update usually carry a hidden NORECOMPUTE flag, set when an index was created. This post builds a demo table, shows the flagged statistic go stale while its neighbor updates itself, and lists every flagged statistic in a database. It also shows which maintenance commands clear the flag and which keep it.
SQL SERVER – 7 Follow Up Answers to Remove Bookmark Lookup
My video on bookmark lookups brought many questions. Here are 7 follow up answers to remove bookmark lookup doubts, starting with STATISTICS IO overhead.