[CALCITE-1588] Add SQL syntax to allow approximate LIMIT and distinct-COUNT

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: Julian Hyde
• Created: 18/Jan/17 19:15
• Updated: 22/Feb/19 01:22

Description

Add SQL syntax to allow approximate LIMIT and distinct-COUNT. These will set the properties specified in CALCITE-1587. By default the properties are false, so the query will return exact results.

Exact syntax is to be decided. It could be at the top of the query (therefore affecting every LIMIT or aggregate in the query) or it could be more localized (e.g. COUNT(DISTINCT customerId) APPROXIMATE (WITHIN 10 PERCENT)).

Issue Links

• is related to: CALCITE-2035 Add APPROX_COUNT_DISTINCT aggregate function
• is related to: PHOENIX-3390 Custom UDAF for HyperLogLogPlus
• is related to: PHOENIX-418 Support approximate COUNT DISTINCT
• relates to: CALCITE-1670 Count distinct on druid is translated to Cardinality aggregator which is approximate
• relates to: CALCITE-1587 Druid adapter: topN returns approximate results