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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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bool fix_fields(THD *thd, Item **ref);
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virtual bool exec(bool full_scan);
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virtual void fix_length_and_dec();
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table_map used_tables() const;
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table_map not_null_tables() const { return 0; }
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bool transformed;
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/* Used to trigger on/off conditions that were pushed down to subselect */
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bool enable_pushed_conds;
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bool *pushed_cond_guards;
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bool *get_cond_guard(int i)
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return pushed_cond_guards ? pushed_cond_guards + i : NULL;
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void set_cond_guard_var(int i, bool v) { pushed_cond_guards[i]= v; }
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bool have_guarded_conds() { return test(pushed_cond_guards); }
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Item_func_not_all *upper_item; // point on NOT/NOP before ALL/SOME subquery
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Item_in_subselect(Item * left_expr, st_select_lex *select_lex);
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Item_in_subselect()
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:Item_exists_subselect(), optimizer(0), abort_on_null(0), transformed(0),
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enable_pushed_conds(TRUE), upper_item(0)
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pushed_cond_guards(NULL), upper_item(0)
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subs_type substype() { return IN_SUBS; }
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full_scan TRUE - Pushed-down predicates are disabled, the engine
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must disable made based on those predicates.
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FALSE - Pushed-down predicates are in effect.
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Execute the engine. The result of execution is subquery value that is
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either captured by previously set up select_result-based 'sink' or
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stored somewhere by the exec() method itself.
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A required side effect: if full_scan==TRUE, subselect_engine->no_rows()
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should return correct result.
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A required side effect: If at least one pushed-down predicate is
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disabled, subselect_engine->no_rows() must return correct result after
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1 - Either an execution error, or the engine was be "changed", and
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1 - Either an execution error, or the engine was "changed", and the
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caller should call exec() again for the new engine.
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virtual int exec(bool full_scan)= 0;
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virtual int exec()= 0;
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virtual uint cols()= 0; /* return number of columns in select */
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virtual uint8 uncacheable()= 0; /* query is uncacheable */
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enum Item_result type() { return res_type; }
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enum_field_types field_type() { return res_field_type; }
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virtual void exclude()= 0;
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bool may_be_null() { return maybe_null; };
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virtual bool may_be_null() { return maybe_null; };
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virtual table_map upper_select_const_tables()= 0;
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static table_map calc_const_tables(TABLE_LIST *);
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virtual void print(String *str)= 0;
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struct st_join_table;
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A subquery execution engine that evaluates the subquery by doing one index
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lookup in a unique index.
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This engine is used to resolve subqueries in forms
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outer_expr IN (SELECT tbl.unique_key FROM tbl WHERE subq_where)
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(oe1, .. oeN) IN (SELECT uniq_key_part1, ... uniq_key_partK
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FROM tbl WHERE subqwhere)
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i.e. the subquery is a single table SELECT without GROUP BY, aggregate
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class subselect_uniquesubquery_engine: public subselect_engine
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st_join_table *tab;
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Item *cond; /* The WHERE condition of subselect */
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TRUE<=> last execution produced empty set. Valid only when left
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expression is NULL.
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/* FALSE for 'ref', TRUE for 'ref-or-null'. */
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The "having" clause. This clause (further reffered to as "artificial
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having") was inserted by subquery transformation code. It contains
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Item(s) that have a side-effect: they record whether the subquery has
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produced a row with NULL certain components. We need to use it for cases
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(oe1, oe2) IN (SELECT t.key, t.no_key FROM t1)
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where we do index lookup on t.key=oe1 but need also to check if there
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was a row such that t.no_key IS NULL.
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NOTE: This is currently here and not in the uniquesubquery_engine. Ideally
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it should have been in uniquesubquery_engine in order to allow execution of
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(oe1, oe2) IN (SELECT primary_key, non_key_maybe_null_field FROM tbl)
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We could use uniquesubquery_engine for the first component and let
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Item_is_not_null_test( non_key_maybe_null_field) to handle the second.
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However, subqueries like the above are currently not handled by index
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lookup-based subquery engines, the engine applicability check misses
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them: it doesn't switch the engine for case of artificial having and
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[eq_]ref access (only for artifical having + ref_or_null or no having).
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The above example subquery is handled as a full-blown SELECT with eq_ref
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Due to this limitation, the "artificial having" currently needs to be
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checked by only in indexsubquery_engine.
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// constructor can assign THD because it will be called after JOIN::prepare
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subselect_indexsubquery_engine(THD *thd, st_join_table *tab_arg,
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Item_subselect *subs, Item *where,
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Item *having_arg, bool chk_null)
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:subselect_uniquesubquery_engine(thd, tab_arg, subs, where),
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check_null(chk_null),
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int exec(bool full_scan);
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void print (String *str);
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sql/item_subselect.h
