Joining Temporary Tables with Permanent Tables in MySQL
Yes — MySQL fully allows JOINs between temporary tables and permanent tables. Temporary tables behave like normal tables within the same session, so you can join them using INNER JOIN, LEFT JOIN, RIGHT JOIN, etc. However, there are important limitations to be aware of.
Temporary tables exist only for the duration of your session.
They are stored either in memory or disk depending on size.
They can be joined with permanent tables exactly like normal tables.
Indexes can be created on temporary tables and are used by the optimizer.
Temporary tables are visible only to the session that created them — no other session can join them.
You cannot create a foreign key that references or is referenced by a temporary table.
Temporary table names can shadow permanent tables with the same name (the temporary table takes precedence).
Replication with temporary tables may require careful handling in statement-based replication.
JOINs with temporary tables are generally fast, especially when the temporary table is small.
Adding indexes to temporary tables can significantly speed up JOINs.
Large temporary tables may spill to disk, increasing I/O cost.
MySQL optimizer treats them like normal tables, but cannot use statistics stored in the data dictionary — it relies on session-level statistics only.
Always index columns used in JOIN conditions.
Use temporary tables for staging, filtering, or transforming data before heavier JOIN operations.
Avoid extremely large temporary tables — consider a persistent staging table instead.
Choose names carefully to avoid conflicts with permanent tables.