APPX_COUNT_DISTINCT Query Option (Impala 2.0 or higher only)
When the APPX_COUNT_DISTINCT query option is set to
TRUE, Impala implicitly converts COUNT(DISTINCT)
operations to the NDV() function calls. The resulting count is
approximate rather than precise. Enable the query option when a tolerable amount of error
is acceptable in order to obtain faster query results than with a COUNT
(DISTINCT) queries.
Type: Boolean; recognized values are 1 and 0, or true and
false; any other value interpreted as false
Default: false (shown as 0 in output of SET
statement)
Related information: