Changes in MySQL HeatWave 8.0.25 (2021-05-11, General Availability)

Functionality Added or Changed

• Support was added for CAST() of ENUM column values to CHAR or VARCHAR where the ENUM value is cast to a FLOAT value, as in the following example:

  SELECT CAST(CAST(enum_col AS FLOAT) AS CHAR(3)) FROM tbl_name;

  (Bug #32618454)

• Support was added for SELECT DISTINCT queries that order the result set by a column that is not defined in the SELECT list. For example, the following query can now be offloaded to MySQL HeatWave for execution:

  SELECT DISTINCT a FROM t1 ORDER BY c DESC;

  (Bug #32583856)

• Query plan statistics are now collected and stored in a statistics cache when a query is executed in MySQL HeatWave. When a new query shares query execution plan nodes with previously executed queries, the actual statistics collected from previously executed queries are used instead of estimated statistics, which improves query execution plans, cost estimations, execution times, and memory efficiency.

  The statistics cache is an LRU structure. When cache capacity is reached, the least recently used entries are evicted from the cache as new entries are added. The maximum number of entries permitted in the statistics cache is defined by the rapid_stats_cache_max_entries setting. The number of entries permitted by default is 65536, which is enough to store statistics for 4000 to 5000 unique queries of medium complexity. (WL #14503)

• Support was added for:

  • CAST() AS YEAR. Both variable-length and dictionary-encoded string columns values are supported.

  • The FORMAT() function. Variable-length-encoded string columns are not supported.

  (WL #14511)