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record per key statistics on keys generated for derived tables are missing, causing a fallback to the usage of MATCHING_ROWS_IN_OTHER_TABLE in best_access_path(). This can grossly overestimate the number of rows expected during a join and cause a bad join order. This patch tries to infer a few simple things about the derived table, like when the key being created matches the group by list inside (if any) inside the derived table. Approved by Sergei Petrunia (sergey@mariadb.com) Tested by Lena Startseva (lena.startseva@mariadb.com)
11 lines
316 B
C
11 lines
316 B
C
#ifndef OPT_GROUP_BY_CARDINALITY
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#define OPT_GROUP_BY_CARDINALITY
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double estimate_post_group_cardinality(JOIN *join, double join_output_card);
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void infer_derived_key_statistics(st_select_lex_unit* derived,
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KEY *keyinfo,
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uint key_parts);
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#endif
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