Details
Description
Looks like it is possible to skip the building sorted Ordered_key structures for subselect_rowid_merge_engine when there is only one key in the materialized subquery.
We have predicate
left_expr IN (SELECT <subq1>)
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where left_expr is a scalar (not a tuple). The logic in this case looks as follows:
if (left_expr is NULL) {
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if (subq1 produced any rows) {
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// note that we don't care if subq1 has produced
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// NULLs or not.
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NULL IN (<some values>) -> UNKNOWN, i.e. NULL.
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} else {
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NULL IN ({empty-set}) -> FALSE.
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}
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} else {
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// left_expr is a non-NULL value
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if (subq1 output has a match for left_expr) {
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left_expr IN (..., left_expr ...) -> TRUE
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} else {
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// no "known" matches.
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if (subq1 output has a NULL) {
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left_expr IN ( ... NULL ...) ->
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(NULL could have been a match or not)
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-> NULL.
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} else {
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// subq1 didn't produce any "UNKNOWNs" so
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// we're positive there weren't any matches
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-> FALSE.
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}
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}
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}
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Attachments
Issue Links
- relates to
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MDEV-34041 Additional information for materialized subqueries must be displayed in EXPLAIN/ANALYZE FORMAT=JSON
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- Closed
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