Concepts·MySQL
MySQL SQL Mode and Strict Behaviour
sql_mode decides whether bad data is an error or a silent correction. Relaxing it turns the out-of-range failure from the constraints guide into a row that stores 99999999.99 and says nothing.
Configuration Guide 15 of 45 Intermediate
- OSUbuntu 26.04 LTS
- MySQL8.4.10-0ubuntu0.26.04.1
- EngineInnoDB (default)
- TimeAbout 15 min
Strict mode has been the default since 5.7. Servers upgraded from 5.6 often carry a relaxed sql_mode forward in their config, which is where most surprises of this kind come from.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| db-a01 | 192.168.0.81 | Ubuntu 26.04 LTS | Primary / Source / Replica Set Member 1 | 2 Core | 4 GB | 50 GB |
This guide includes
Use this when bad data is being silently corrected instead of refused. This matters because sql_mode is what decides that - turning strict mode off makes a previously failing insert succeed, storing a value you did not mean.
- reading the modes this server actually enforces
- turning strict mode off, and repeating a statement that failed before
- confirming the bad row really is there, from an ordinary session
Before you start
- The
customerstable from the schema-data track.
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Read the modes this server enforces
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Turn strict mode off and repeat a statement that failed
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Confirm the bad row is really there