diff options
Diffstat (limited to 'sql/opt_sum.cc')
| -rw-r--r-- | sql/opt_sum.cc | 92 |
1 files changed, 67 insertions, 25 deletions
diff --git a/sql/opt_sum.cc b/sql/opt_sum.cc index ecfa97586e9..d5a4149f243 100644 --- a/sql/opt_sum.cc +++ b/sql/opt_sum.cc @@ -1,4 +1,4 @@ -/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB +/* Copyright (C) 2000-2003 MySQL AB This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -22,28 +22,55 @@ static bool find_range_key(TABLE_REF *ref, Field* field,COND *cond); -/***************************************************************************** -** This function is only called for queries with sum functions and no -** GROUP BY part. -** This substitutes constants for some COUNT(), MIN() and MAX() functions. -** The function returns 1 if all items was resolved and -1 on impossible -** conditions -****************************************************************************/ +/* + Substitutes constants for some COUNT(), MIN() and MAX() functions. + + SYNOPSIS + opt_sum_query() + tables Tables in query + all_fields All fields to be returned + conds WHERE clause + + NOTE: + This function is only called for queries with sum functions and no + GROUP BY part. + + RETURN VALUES + 0 No errors + 1 if all items was resolved + -1 on impossible conditions +*/ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds) { List_iterator_fast<Item> it(all_fields); - int const_result=1; - bool recalc_const_item=0; - table_map removed_tables=0; + int const_result= 1; + bool recalc_const_item= 0; + table_map removed_tables= 0, outer_tables= 0, used_tables= 0; + table_map where_tables= 0; Item *item; COND *org_conds= conds; - /* Add all ON conditions to WHERE condition */ + if (conds) + where_tables= conds->used_tables(); + + /* Don't replace expression on a table that is part of an outer join */ for (TABLE_LIST *tl=tables; tl ; tl= tl->next) { if (tl->on_expr) - conds= and_expressions(conds, tl->on_expr, &org_conds); + { + outer_tables|= tl->table->map; + + /* + We can't optimise LEFT JOIN in cases where the WHERE condition + restricts the table that is used, like in: + SELECT MAX(t1.a) FROM t1 LEFT JOIN t2 join-condition + WHERE t2.field IS NULL; + */ + if (tl->table->map & where_tables) + return 0; + } + used_tables|= tl->table->map; } /* @@ -68,8 +95,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds) TABLE_LIST *table; for (table=tables; table ; table=table->next) { - if (table->on_expr || (table->table->file->table_flags() & - HA_NOT_EXACT_COUNT)) + if (outer_tables || (table->table->file->table_flags() & + HA_NOT_EXACT_COUNT)) { const_result=0; // Can't optimize left join break; @@ -99,21 +126,35 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds) byte key_buff[MAX_KEY_LENGTH]; TABLE_REF ref; ref.key_buff=key_buff; + Item_field *item_field= ((Item_field*) expr); + TABLE *table= item_field->field->table; - if (!find_range_key(&ref, ((Item_field*) expr)->field,conds)) + if ((outer_tables & table->map) || + (!find_range_key(&ref, item_field->field,conds))) { const_result=0; break; } - TABLE *table=((Item_field*) expr)->field->table; - bool error=table->file->index_init((uint) ref.key); + bool error= table->file->index_init((uint) ref.key); + enum ha_rkey_function find_flag= HA_READ_KEY_OR_NEXT; + uint prefix_len= ref.key_length; + /* + If we are doing MIN() on a column with NULL fields + we must read the key after the NULL column + */ + if (item_field->field->null_bit) + { + ref.key_buff[ref.key_length++]=1; + find_flag= HA_READ_AFTER_KEY; + } + if (!ref.key_length) error=table->file->index_first(table->record[0]) !=0; else error=table->file->index_read(table->record[0],key_buff, ref.key_length, - HA_READ_KEY_OR_NEXT) || - key_cmp(table, key_buff, ref.key, ref.key_length); + find_flag) || + key_cmp(table, key_buff, ref.key, prefix_len); if (table->key_read) { table->key_read=0; @@ -121,7 +162,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds) } table->file->index_end(); if (error) - return -1; // Impossible query + return -1; // No rows matching where removed_tables|= table->map; } else if (!expr->const_item()) // This is VERY seldom false @@ -147,13 +188,14 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds) byte key_buff[MAX_KEY_LENGTH]; TABLE_REF ref; ref.key_buff=key_buff; + TABLE *table=((Item_field*) expr)->field->table; - if (!find_range_key(&ref, ((Item_field*) expr)->field,conds)) + if ((outer_tables & table->map) || + !find_range_key(&ref, ((Item_field*) expr)->field,conds)) { const_result=0; break; } - TABLE *table=((Item_field*) expr)->field->table; if ((table->file->table_flags() & HA_NOT_READ_AFTER_KEY)) { const_result=0; @@ -203,8 +245,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds) const_result=0; } } - if (conds && (conds->used_tables() & ~ removed_tables)) - const_result=0; + if (used_tables != removed_tables) + const_result=0; // We didn't remove all tables return const_result; } |