How forgiving the database is.
WHAT A PERMISSIVE MODE DOES
Accepts invalid data with a warning, storing something approximate.
WHAT THAT PRODUCES
Truncated strings Zeroes where a date was invalid Values silently altered
WHY THAT IS DANGEROUS
Data is wrong, and nothing failed.
WHAT STRICT MODE DOES
Rejects the statement instead.
WHY THAT IS CORRECT
An error is recoverable; silently wrong data is not.
WHAT TO ENABLE
Strict mode, and the related settings that reject invalid dates and division by zero.
WHAT ELSE TO ENABLE
Strict grouping behaviour, so ambiguous queries are rejected.
WHY THAT ONE MATTERS
It prevents queries returning an arbitrary value from a group.
WHAT TO EXPECT ON ENABLING IT
Existing applications producing errors.
WHY THAT IS GOOD NEWS
Those errors were previously silent corruption.
WHAT TO DO
Enable it in development first, fix what breaks, then production.
WHAT TO CHECK ON AN INHERITED SYSTEM
Which modes are active.
HOW
Query the mode variable.
WHAT TO DOCUMENT
The intended modes, and keep environments matching.
WHAT TO BE CAREFUL WITH
Applications relying on permissive behaviour.
WHAT THAT INDICATES
Defects that have been masked.
