diff options
Diffstat (limited to 'sql/sql_join_cache.h')
| -rw-r--r-- | sql/sql_join_cache.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/sql/sql_join_cache.h b/sql/sql_join_cache.h index d0bf4761f65..eb943b28be2 100644 --- a/sql/sql_join_cache.h +++ b/sql/sql_join_cache.h @@ -531,6 +531,22 @@ protected: /* Check matching to a partial join record from the join buffer */ bool check_match(uchar *rec_ptr); + /* + Determine whether it is enough to check only the first match for + the table and skip other possible matches. This is used for semi-joins + and 'not exists' optimization. + + NOTE: 'not exists' optimization is not yet implemented for linked + join buffers so is not applicable if prev_cache is not NULL + */ + bool check_only_first_match(JOIN_TAB *tab) + { + return tab->is_inner_table_of_semi_join_with_first_match() || + (tab->is_inner_table_of_outer_join() && + tab->table->reginfo.not_exists_optimize && + !prev_cache); + } + /* This constructor creates an unlinked join cache. The cache is to be used to join table 'tab' to the result of joining the previous tables |