SQL
Trigger Use Cases and Limitations
What triggers are genuinely good at, the costs they impose, and the honest list of reasons teams end up removing them.
#Performance
Making queries and schemas faster.
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SQL
User Defined Functions
Functions return a value and can be used inside a query. Learn CREATE FUNCTION, determinism, the difference from procedures, and the performance trap.
SQL
Anomalies and Denormalisation
The three anomalies normalisation prevents, and the disciplined way to reintroduce redundancy when reads genuinely demand it.
SQL
Subqueries in SELECT, FROM and WHERE: Join vs Subquery vs EXISTS
The same question answered four ways, with a straight comparison of readability, NULL safety and cost - and a rule for choosing between them.
SQL
ORDER BY, LIMIT and Pagination
Sorting on one or many columns, NULL placement, and the four dialect specific ways to fetch page two of a result set - including why OFFSET gets slow.