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materialized_from_subquery

Short Description

materialized_from_subquery shows the optimizer materializing a subquery into a temporary table to improve efficiency

materialized_from_subquery shows the optimizer materializing a subquery into a temporary table (typically in memory) to improve efficiency. The first run of the subquery builds the temporary table (possibly with an additional hash index). Subsequently, rows are are read from the temporary table rather than having to re-execute the subquery, reducing IO.

In order to be able to materialize subqueries, the [materialization](https://dev.mysql.com/doc/refman/8.0/en/switchable-optimizations.html#optflag_materialization) optimizer switch system variable needs to be enabled.

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