A value derived from other columns is usually maintained by application code or a trigger, and both drift. A generated column is computed by the server and cannot…
The rule that makes aggregates useful is that one transaction touches one aggregate. Everything else follows: what belongs inside, what is referenced by id, and where consistency is…
Indexing a 255-character column costs 255 characters per row in the index, and for a lookup that is unique within the first dozen characters most of that is…
Seconds_Behind_Master is the number everyone alerts on and it measures one thing: how far behind the applying thread is on the transaction it is currently executing. It reads…
EXPLAIN says what the optimiser chose. It does not say why, so when a perfectly good index is ignored there is nothing to read. The optimizer trace is…
The default sql_mode changed, and with it a decade of behaviour: inserting a string into a numeric column, a date of 0000-00-00, or more characters than the column…