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Adding comments as per Monty's request.

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unknown
2002-12-14 15:13:25 +02:00
parent aec84fd984
commit 2b29b55c55
1 changed files with 39 additions and 4 deletions
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43
sql/sql_derived.cc
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@ -27,13 +27,33 @@
static const char *any_db="*any*"; // Special symbol for check_access static const char *any_db="*any*"; // Special symbol for check_access
/*
Resolve derived tables in all queries
SYNOPSIS
mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
thd Thread handle
lex LEX for this thread
unit node that contains all SELECT's for derived tables
t TABLE_LIST for the upper SELECT
IMPLEMENTATION
Derived table is resolved with temporary table. It is created based on the
queries defined. After temporary table is created, if this is not EXPLAIN,
then the entire unit / node is deleted. unit is deleted if UNION is used
for derived table and node is deleted is it is a simple SELECT.
After table creation, the above TABLE_LIST is updated with a new table.
This function is called before any command containing derived table is executed.
TODO: To move creation of derived tables IN open_and_lock_tables()
*/
int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t) int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
{ {
/*
TODO: make derived tables with union inside (now only 1 SELECT may be
procesed)
*/
SELECT_LEX *sl= unit->first_select(); SELECT_LEX *sl= unit->first_select();
List<Item> item_list; List<Item> item_list;
TABLE *table; TABLE *table;
@ -45,6 +65,12 @@ int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
DBUG_ENTER("mysql_derived"); DBUG_ENTER("mysql_derived");
/*
In create_total_list, derived tables have to be treated in case of EXPLAIN,
This is because unit/node is not deleted in that case. Current code in this
function has to be improved to recognize better when this function is called
from derived tables and when from other functions.
*/
if (is_union && unit->create_total_list(thd, lex, &tables)) if (is_union && unit->create_total_list(thd, lex, &tables))
DBUG_RETURN(-1); DBUG_RETURN(-1);
@ -65,6 +91,15 @@ int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
{ {
if (is_union) if (is_union)
{ {
/*
The following code is a re-do of fix_tables_pointers() found in sql_select.cc
for UNION's within derived tables. The only difference is in navigation, as in
derived tables we care for this level only.
fix_tables_pointers makes sure that in UNION's we do not open single table twice
if found in different SELECT's.
*/
for (SELECT_LEX *sel= sl; for (SELECT_LEX *sel= sl;
sel; sel;
sel= sel->next_select()) sel= sel->next_select())