The SELECT would examine more than Max_join_size rows error analysis MYSQL

Use a linked table to query a large table, 21 fields, nearly 40 million records bar. The other table is tens of thousands of of the recorded volume.
The report error message is:


#1104 the SELECT would examine more than max_join_size rows;
Check your WHERE and use set Sql_big_selects=1 or SET max_join_size=#
If the SELECT is okay.


The reasons for this analysis are:
1, the temp table is too small. The intermediate set of the query cannot be mounted.
2, or no index or settings are bad.
3, this big table is best not to query the table. 40 million * 60,000, that's 240 million.

The SELECT would examine more than Max_join_size rows error analysis MYSQL