SQL Server suggests missing indexes in the execution plan and the DMVs, but copying them blindly creates duplicates and slows writes. Here’s how to find them, read them, and decide.
The date functions you’ll use most in SQL Server and MySQL: current date, DATEADD, DATEDIFF, month end and formatting, plus the BETWEEN mistake that makes monthly totals wrong.
UNION removes duplicates, UNION ALL keeps every row and is faster. Learn when to use each, the rules every UNION must follow, and the trap that can make your totals wrong.
WHERE filters rows before grouping. HAVING filters groups after GROUP BY. See the difference with a simple sales example, the logical query order, and common mistakes.
You created an index but SQL Server still scans the table. Here are the 8 most common reasons, from functions on columns to implicit conversions, with the fix for each.
Execution plans look confusing at first. Learn to read a SQL Server plan step by step: right to left, arrow thickness, cost percentages, the operators that matter, and a real example.
Seeing an Index Spool (Eager Spool) in your SQL Server execution plan? Here is what it means, why SQL Server builds a temporary index on every run, and the one index that makes it disappear.
Understand how SQL injection happens and how to prevent it with parameterised queries in PHP, Laravel, Delphi and C#, plus extra defences.
How database backups work: full, differential and log backups, point-in-time restore, the 3-2-1 rule, and commands for SQL Server, MySQL and PostgreSQL.
Learn what SQL triggers are, how to write them in SQL Server, MySQL and PostgreSQL, and when they help or hurt, with a price history example.
