The whole category summarised.
A BACKUP THAT HAS NEVER BEEN RESTORED IS NOT A BACKUP
Test the restore on a schedule, time it, and write the procedure down. Replication is not a backup — a deletion replicates instantly to every copy.
INDEXES EXPLAIN MOST PERFORMANCE PROBLEMS
Missing ones are why applications work for a year and degrade suddenly. Read the plan, compare rows examined against rows returned, and index every foreign key.
FIX QUERIES BEFORE TOUCHING CONFIGURATION
Tuning first spends effort where the problem is not, and scaling hardware to hide an unindexed query turns a fixable fault into a permanent cost.
RUN THE SELECT BEFORE THE UPDATE OR DELETE
It shows exactly which rows will change, and it is the habit that prevents the worst incidents.
NEVER FLOATING POINT FOR MONEY, NEVER TEXT FOR DATES, ALWAYS THE FULL ENCODING
The third one corrupts text permanently on import, and it cannot be undone.
PUT CONSTRAINTS IN THE DATABASE
Applications change, scripts bypass them, and several things may write. Cleaning bad data without adding the constraint means cleaning it again.
PARAMETERISE EVERY QUERY AND GRANT MINIMUM PRIVILEGES
One prevents injection; the other limits what it can reach.
BIND THE DATABASE TO THE LOCAL ADDRESS
Exposed databases are scanned continuously, and this single change prevents most attacks outright.
