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mariadb/sql/opt_sum.cc
monty@mysql.com 74cc73d461 This changeset is largely a handler cleanup changeset (WL#3281), but includes fixes and cleanups that was found necessary while testing the handler changes 
Changes that requires code changes in other code of other storage engines.
(Note that all changes are very straightforward and one should find all issues
by compiling a --debug build and fixing all compiler errors and all
asserts in field.cc while running the test suite),

- New optional handler function introduced: reset()
  This is called after every DML statement to make it easy for a handler to
  statement specific cleanups.
  (The only case it's not called is if force the file to be closed)

- handler::extra(HA_EXTRA_RESET) is removed. Code that was there before
  should be moved to handler::reset()

- table->read_set contains a bitmap over all columns that are needed
  in the query.  read_row() and similar functions only needs to read these
  columns
- table->write_set contains a bitmap over all columns that will be updated
  in the query. write_row() and update_row() only needs to update these
  columns.
  The above bitmaps should now be up to date in all context
  (including ALTER TABLE, filesort()).

  The handler is informed of any changes to the bitmap after
  fix_fields() by calling the virtual function
  handler::column_bitmaps_signal(). If the handler does caching of
  these bitmaps (instead of using table->read_set, table->write_set),
  it should redo the caching in this code. as the signal() may be sent
  several times, it's probably best to set a variable in the signal
  and redo the caching on read_row() / write_row() if the variable was
  set.

- Removed the read_set and write_set bitmap objects from the handler class

- Removed all column bit handling functions from the handler class.
  (Now one instead uses the normal bitmap functions in my_bitmap.c instead
  of handler dedicated bitmap functions)

- field->query_id is removed. One should instead instead check
  table->read_set and table->write_set if a field is used in the query.

- handler::extra(HA_EXTRA_RETRIVE_ALL_COLS) and
  handler::extra(HA_EXTRA_RETRIEVE_PRIMARY_KEY) are removed. One should now
  instead use table->read_set to check for which columns to retrieve.

- If a handler needs to call Field->val() or Field->store() on columns
  that are not used in the query, one should install a temporary
  all-columns-used map while doing so. For this, we provide the following
  functions:

  my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->read_set);
  field->val();
  dbug_tmp_restore_column_map(table->read_set, old_map);

  and similar for the write map:

  my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->write_set);
  field->val();
  dbug_tmp_restore_column_map(table->write_set, old_map);

  If this is not done, you will sooner or later hit a DBUG_ASSERT
  in the field store() / val() functions.
  (For not DBUG binaries, the dbug_tmp_restore_column_map() and
  dbug_tmp_restore_column_map() are inline dummy functions and should
  be optimized away be the compiler).

- If one needs to temporary set the column map for all binaries (and not
  just to avoid the DBUG_ASSERT() in the Field::store() / Field::val()
  methods) one should use the functions tmp_use_all_columns() and
  tmp_restore_column_map() instead of the above dbug_ variants.

- All 'status' fields in the handler base class (like records,
  data_file_length etc) are now stored in a 'stats' struct. This makes
  it easier to know what status variables are provided by the base
  handler.  This requires some trivial variable names in the extra()
  function.

- New virtual function handler::records().  This is called to optimize
  COUNT(*) if (handler::table_flags() & HA_HAS_RECORDS()) is true.
  (stats.records is not supposed to be an exact value. It's only has to
  be 'reasonable enough' for the optimizer to be able to choose a good
  optimization path).

- Non virtual handler::init() function added for caching of virtual
  constants from engine.

- Removed has_transactions() virtual method. Now one should instead return
  HA_NO_TRANSACTIONS in table_flags() if the table handler DOES NOT support
  transactions.

- The 'xxxx_create_handler()' function now has a MEM_ROOT_root argument
  that is to be used with 'new handler_name()' to allocate the handler
  in the right area.  The xxxx_create_handler() function is also
  responsible for any initialization of the object before returning.

  For example, one should change:

  static handler *myisam_create_handler(TABLE_SHARE *table)
  {
    return new ha_myisam(table);
  }

  ->

  static handler *myisam_create_handler(TABLE_SHARE *table, MEM_ROOT *mem_root)
  {
    return new (mem_root) ha_myisam(table);
  }

- New optional virtual function: use_hidden_primary_key().
  This is called in case of an update/delete when
  (table_flags() and HA_PRIMARY_KEY_REQUIRED_FOR_DELETE) is defined
  but we don't have a primary key. This allows the handler to take precisions
  in remembering any hidden primary key to able to update/delete any
  found row. The default handler marks all columns to be read.

- handler::table_flags() now returns a ulonglong (to allow for more flags).

- New/changed table_flags()
  - HA_HAS_RECORDS	    Set if ::records() is supported
  - HA_NO_TRANSACTIONS	    Set if engine doesn't support transactions
  - HA_PRIMARY_KEY_REQUIRED_FOR_DELETE
                            Set if we should mark all primary key columns for
			    read when reading rows as part of a DELETE
			    statement. If there is no primary key,
			    all columns are marked for read.
  - HA_PARTIAL_COLUMN_READ  Set if engine will not read all columns in some
			    cases (based on table->read_set)
 - HA_PRIMARY_KEY_ALLOW_RANDOM_ACCESS
   			    Renamed to HA_PRIMARY_KEY_REQUIRED_FOR_POSITION.
 - HA_DUPP_POS              Renamed to HA_DUPLICATE_POS
 - HA_REQUIRES_KEY_COLUMNS_FOR_DELETE
			    Set this if we should mark ALL key columns for
			    read when when reading rows as part of a DELETE
			    statement. In case of an update we will mark
			    all keys for read for which key part changed
			    value.
  - HA_STATS_RECORDS_IS_EXACT
			     Set this if stats.records is exact.
			     (This saves us some extra records() calls
			     when optimizing COUNT(*))
			    

- Removed table_flags()
  - HA_NOT_EXACT_COUNT     Now one should instead use HA_HAS_RECORDS if
			   handler::records() gives an exact count() and
			   HA_STATS_RECORDS_IS_EXACT if stats.records is exact.
  - HA_READ_RND_SAME	   Removed (no one supported this one)

- Removed not needed functions ha_retrieve_all_cols() and ha_retrieve_all_pk()

- Renamed handler::dupp_pos to handler::dup_pos

- Removed not used variable handler::sortkey


Upper level handler changes:

- ha_reset() now does some overall checks and calls ::reset()
- ha_table_flags() added. This is a cached version of table_flags(). The
  cache is updated on engine creation time and updated on open.


MySQL level changes (not obvious from the above):

- DBUG_ASSERT() added to check that column usage matches what is set
  in the column usage bit maps. (This found a LOT of bugs in current
  column marking code).

- In 5.1 before, all used columns was marked in read_set and only updated
  columns was marked in write_set. Now we only mark columns for which we
  need a value in read_set.

- Column bitmaps are created in open_binary_frm() and open_table_from_share().
  (Before this was in table.cc)

- handler::table_flags() calls are replaced with handler::ha_table_flags()

- For calling field->val() you must have the corresponding bit set in
  table->read_set. For calling field->store() you must have the
  corresponding bit set in table->write_set. (There are asserts in
  all store()/val() functions to catch wrong usage)

- thd->set_query_id is renamed to thd->mark_used_columns and instead
  of setting this to an integer value, this has now the values:
  MARK_COLUMNS_NONE, MARK_COLUMNS_READ, MARK_COLUMNS_WRITE
  Changed also all variables named 'set_query_id' to mark_used_columns.

- In filesort() we now inform the handler of exactly which columns are needed
  doing the sort and choosing the rows.

- The TABLE_SHARE object has a 'all_set' column bitmap one can use
  when one needs a column bitmap with all columns set.
  (This is used for table->use_all_columns() and other places)

- The TABLE object has 3 column bitmaps:
  - def_read_set     Default bitmap for columns to be read
  - def_write_set    Default bitmap for columns to be written
  - tmp_set          Can be used as a temporary bitmap when needed.
  The table object has also two pointer to bitmaps read_set and write_set
  that the handler should use to find out which columns are used in which way.

- count() optimization now calls handler::records() instead of using
  handler->stats.records (if (table_flags() & HA_HAS_RECORDS) is true).

- Added extra argument to Item::walk() to indicate if we should also
  traverse sub queries.

- Added TABLE parameter to cp_buffer_from_ref()

- Don't close tables created with CREATE ... SELECT but keep them in
  the table cache. (Faster usage of newly created tables).


New interfaces:

- table->clear_column_bitmaps() to initialize the bitmaps for tables
  at start of new statements.

- table->column_bitmaps_set() to set up new column bitmaps and signal
  the handler about this.

- table->column_bitmaps_set_no_signal() for some few cases where we need
  to setup new column bitmaps but don't signal the handler (as the handler
  has already been signaled about these before). Used for the momement
  only in opt_range.cc when doing ROR scans.

- table->use_all_columns() to install a bitmap where all columns are marked
  as use in the read and the write set.

- table->default_column_bitmaps() to install the normal read and write
  column bitmaps, but not signaling the handler about this.
  This is mainly used when creating TABLE instances.

- table->mark_columns_needed_for_delete(),
  table->mark_columns_needed_for_delete() and
  table->mark_columns_needed_for_insert() to allow us to put additional
  columns in column usage maps if handler so requires.
  (The handler indicates what it neads in handler->table_flags())

- table->prepare_for_position() to allow us to tell handler that it
  needs to read primary key parts to be able to store them in
  future table->position() calls.
  (This replaces the table->file->ha_retrieve_all_pk function)

- table->mark_auto_increment_column() to tell handler are going to update
  columns part of any auto_increment key.

- table->mark_columns_used_by_index() to mark all columns that is part of
  an index.  It will also send extra(HA_EXTRA_KEYREAD) to handler to allow
  it to quickly know that it only needs to read colums that are part
  of the key.  (The handler can also use the column map for detecting this,
  but simpler/faster handler can just monitor the extra() call).

- table->mark_columns_used_by_index_no_reset() to in addition to other columns,
  also mark all columns that is used by the given key.

- table->restore_column_maps_after_mark_index() to restore to default
  column maps after a call to table->mark_columns_used_by_index().

- New item function register_field_in_read_map(), for marking used columns
  in table->read_map. Used by filesort() to mark all used columns

- Maintain in TABLE->merge_keys set of all keys that are used in query.
  (Simplices some optimization loops)

- Maintain Field->part_of_key_not_clustered which is like Field->part_of_key
  but the field in the clustered key is not assumed to be part of all index.
  (used in opt_range.cc for faster loops)

-  dbug_tmp_use_all_columns(), dbug_tmp_restore_column_map()
   tmp_use_all_columns() and tmp_restore_column_map() functions to temporally
   mark all columns as usable.  The 'dbug_' version is primarily intended
   inside a handler when it wants to just call Field:store() & Field::val()
   functions, but don't need the column maps set for any other usage.
   (ie:: bitmap_is_set() is never called)

- We can't use compare_records() to skip updates for handlers that returns
  a partial column set and the read_set doesn't cover all columns in the
  write set. The reason for this is that if we have a column marked only for
  write we can't in the MySQL level know if the value changed or not.
  The reason this worked before was that MySQL marked all to be written
  columns as also to be read. The new 'optimal' bitmaps exposed this 'hidden
  bug'.

- open_table_from_share() does not anymore setup temporary MEM_ROOT
  object as a thread specific variable for the handler. Instead we
  send the to-be-used MEMROOT to get_new_handler().
  (Simpler, faster code)



Bugs fixed:

- Column marking was not done correctly in a lot of cases.
  (ALTER TABLE, when using triggers, auto_increment fields etc)
  (Could potentially result in wrong values inserted in table handlers
  relying on that the old column maps or field->set_query_id was correct)
  Especially when it comes to triggers, there may be cases where the
  old code would cause lost/wrong values for NDB and/or InnoDB tables.

- Split thd->options flag OPTION_STATUS_NO_TRANS_UPDATE to two flags:
  OPTION_STATUS_NO_TRANS_UPDATE and OPTION_KEEP_LOG.
  This allowed me to remove some wrong warnings about:
  "Some non-transactional changed tables couldn't be rolled back"

- Fixed handling of INSERT .. SELECT and CREATE ... SELECT that wrongly reset
  (thd->options & OPTION_STATUS_NO_TRANS_UPDATE) which caused us to loose
  some warnings about
  "Some non-transactional changed tables couldn't be rolled back")

- Fixed use of uninitialized memory in ha_ndbcluster.cc::delete_table()
  which could cause delete_table to report random failures.

- Fixed core dumps for some tests when running with --debug

- Added missing FN_LIBCHAR in mysql_rm_tmp_tables()
  (This has probably caused us to not properly remove temporary files after
  crash)

- slow_logs was not properly initialized, which could maybe cause
  extra/lost entries in slow log.

- If we get an duplicate row on insert, change column map to read and
  write all columns while retrying the operation. This is required by
  the definition of REPLACE and also ensures that fields that are only
  part of UPDATE are properly handled.  This fixed a bug in NDB and
  REPLACE where REPLACE wrongly copied some column values from the replaced
  row.

- For table handler that doesn't support NULL in keys, we would give an error
  when creating a primary key with NULL fields, even after the fields has been
  automaticly converted to NOT NULL.

- Creating a primary key on a SPATIAL key, would fail if field was not
  declared as NOT NULL.


Cleanups:

- Removed not used condition argument to setup_tables

- Removed not needed item function reset_query_id_processor().

- Field->add_index is removed. Now this is instead maintained in
  (field->flags & FIELD_IN_ADD_INDEX)

- Field->fieldnr is removed (use field->field_index instead)

- New argument to filesort() to indicate that it should return a set of
  row pointers (not used columns). This allowed me to remove some references
  to sql_command in filesort and should also enable us to return column
  results in some cases where we couldn't before.

- Changed column bitmap handling in opt_range.cc to be aligned with TABLE
  bitmap, which allowed me to use bitmap functions instead of looping over
  all fields to create some needed bitmaps. (Faster and smaller code)

- Broke up found too long lines

- Moved some variable declaration at start of function for better code
  readability.

- Removed some not used arguments from functions.
  (setup_fields(), mysql_prepare_insert_check_table())

- setup_fields() now takes an enum instead of an int for marking columns
   usage.

- For internal temporary tables, use handler::write_row(),
  handler::delete_row() and handler::update_row() instead of
  handler::ha_xxxx() for faster execution.

- Changed some constants to enum's and define's.

- Using separate column read and write sets allows for easier checking
  of timestamp field was set by statement.

- Remove calls to free_io_cache() as this is now done automaticly in ha_reset()

- Don't build table->normalized_path as this is now identical to table->path
  (after bar's fixes to convert filenames)

- Fixed some missed DBUG_PRINT(.."%lx") to use "0x%lx" to make it easier to
  do comparision with the 'convert-dbug-for-diff' tool.


Things left to do in 5.1:

- We wrongly log failed CREATE TABLE ... SELECT in some cases when using
  row based logging (as shown by testcase binlog_row_mix_innodb_myisam.result)
  Mats has promised to look into this.

- Test that my fix for CREATE TABLE ... SELECT is indeed correct.
  (I added several test cases for this, but in this case it's better that
  someone else also tests this throughly).
  Lars has promosed to do this.
2006-06-04 18:52:22 +03:00

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/* 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
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/*
Optimising of MIN(), MAX() and COUNT(*) queries without 'group by' clause
by replacing the aggregate expression with a constant.
Given a table with a compound key on columns (a,b,c), the following
types of queries are optimised (assuming the table handler supports
the required methods)
SELECT COUNT(*) FROM t1[,t2,t3,...]
SELECT MIN(b) FROM t1 WHERE a=const
SELECT MAX(c) FROM t1 WHERE a=const AND b=const
SELECT MAX(b) FROM t1 WHERE a=const AND b<const
SELECT MIN(b) FROM t1 WHERE a=const AND b>const
SELECT MIN(b) FROM t1 WHERE a=const AND b BETWEEN const AND const
SELECT MAX(b) FROM t1 WHERE a=const AND b BETWEEN const AND const
Instead of '<' one can use '<=', '>', '>=' and '=' as well.
Instead of 'a=const' the condition 'a IS NULL' can be used.
If all selected fields are replaced then we will also remove all
involved tables and return the answer without any join. Thus, the
following query will be replaced with a row of two constants:
SELECT MAX(b), MIN(d) FROM t1,t2
WHERE a=const AND b<const AND d>const
(assuming a index for column d of table t2 is defined)
*/
#include "mysql_priv.h"
#include "sql_select.h"
static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint *range_fl,
uint *key_prefix_length);
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint range_fl, uint prefix_len);
static int maxmin_in_range(bool max_fl, Field* field, COND *cond);
/*
Get exact count of rows in all tables
SYNOPSIS
get_exact_records()
tables List of tables
NOTES
When this is called, we know all table handlers supports HA_HAS_RECORDS
or HA_STATS_RECORDS_IS_EXACT
RETURN
ULONGLONG_MAX Error: Could not calculate number of rows
# Multiplication of number of rows in all tables
*/
static ulonglong get_exact_record_count(TABLE_LIST *tables)
{
ulonglong count= 1;
for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
{
ha_rows tmp= tl->table->file->records();
if ((tmp == HA_POS_ERROR))
return ULONGLONG_MAX;
count*= tmp;
}
return count;
}
/*
Substitutes constants for some COUNT(), MIN() and MAX() functions.
SYNOPSIS
opt_sum_query()
tables list of leaves of join table tree
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 were resolved
-1 on impossible conditions
OR an error number from my_base.h HA_ERR_... if a deadlock or a lock
wait timeout happens, for example
*/
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;
ulonglong count= 1;
bool is_exact_count= TRUE, maybe_exact_count= TRUE;
table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
table_map where_tables= 0;
Item *item;
int error;
if (conds)
where_tables= conds->used_tables();
/*
Analyze outer join dependencies, and, if possible, compute the number
of returned rows.
*/
for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
{
TABLE_LIST *embedded;
for (embedded= tl ; embedded; embedded= embedded->embedding)
{
if (embedded->on_expr)
break;
}
if (embedded)
/* Don't replace expression on a table that is part of an outer join */
{
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;
}
else
used_tables|= tl->table->map;
/*
If the storage manager of 'tl' gives exact row count as part of
statistics (cheap), compute the total number of rows. If there are
no outer table dependencies, this count may be used as the real count.
Schema tables are filled after this function is invoked, so we can't
get row count
*/
if (!(tl->table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT) ||
tl->schema_table)
{
maybe_exact_count&= test(!tl->schema_table &&
(tl->table->file->ha_table_flags() &
HA_HAS_RECORDS));
is_exact_count= FALSE;
count= 1; // ensure count != 0
}
else
{
tl->table->file->info(HA_STATUS_VARIABLE | HA_STATUS_NO_LOCK);
count*= tl->table->file->stats.records;
}
}
/*
Iterate through all items in the SELECT clause and replace
COUNT(), MIN() and MAX() with constants (if possible).
*/
while ((item= it++))
{
if (item->type() == Item::SUM_FUNC_ITEM)
{
Item_sum *item_sum= (((Item_sum*) item));
switch (item_sum->sum_func()) {
case Item_sum::COUNT_FUNC:
/*
If the expr in COUNT(expr) can never be null we can change this
to the number of rows in the tables if this number is exact and
there are no outer joins.
*/
if (!conds && !((Item_sum_count*) item)->args[0]->maybe_null &&
!outer_tables && maybe_exact_count)
{
if (!is_exact_count)
{
if ((count= get_exact_record_count(tables)) == ULONGLONG_MAX)
{
/* Error from handler in counting rows. Don't optimize count() */
const_result= 0;
continue;
}
is_exact_count= 1; // count is now exact
}
((Item_sum_count*) item)->make_const((longlong) count);
recalc_const_item= 1;
}
else
const_result= 0;
break;
case Item_sum::MIN_FUNC:
{
/*
If MIN(expr) is the first part of a key or if all previous
parts of the key is found in the COND, then we can use
indexes to find the key.
*/
Item *expr=item_sum->args[0];
if (expr->real_item()->type() == Item::FIELD_ITEM)
{
byte key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
uint range_fl, prefix_len;
ref.key_buff= key_buff;
Item_field *item_field= (Item_field*) (expr->real_item());
TABLE *table= item_field->field->table;
/*
Look for a partial key that can be used for optimization.
If we succeed, ref.key_length will contain the length of
this key, while prefix_len will contain the length of
the beginning of this key without field used in MIN().
Type of range for the key part for this field will be
returned in range_fl.
*/
if ((outer_tables & table->map) ||
!find_key_for_maxmin(0, &ref, item_field->field, conds,
&range_fl, &prefix_len))
{
const_result= 0;
break;
}
error= table->file->ha_index_init((uint) ref.key, 1);
if (!ref.key_length)
error= table->file->index_first(table->record[0]);
else
error= table->file->index_read(table->record[0],key_buff,
ref.key_length,
range_fl & NEAR_MIN ?
HA_READ_AFTER_KEY :
HA_READ_KEY_OR_NEXT);
if (!error && reckey_in_range(0, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
if (table->key_read)
{
table->key_read= 0;
table->file->extra(HA_EXTRA_NO_KEYREAD);
}
table->file->ha_index_end();
if (error)
{
if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
return -1; // No rows matching WHERE
/* HA_ERR_LOCK_DEADLOCK or some other error */
table->file->print_error(error, MYF(0));
return(error);
}
removed_tables|= table->map;
}
else if (!expr->const_item() || !is_exact_count)
{
/*
The optimization is not applicable in both cases:
(a) 'expr' is a non-constant expression. Then we can't
replace 'expr' by a constant.
(b) 'expr' is a costant. According to ANSI, MIN/MAX must return
NULL if the query does not return any rows. Thus, if we are not
able to determine if the query returns any rows, we can't apply
the optimization and replace MIN/MAX with a constant.
*/
const_result= 0;
break;
}
if (!count)
{
/* If count == 0, then we know that is_exact_count == TRUE. */
((Item_sum_min*) item_sum)->clear(); /* Set to NULL. */
}
else
((Item_sum_min*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_min*) item_sum)->make_const();
recalc_const_item= 1;
break;
}
case Item_sum::MAX_FUNC:
{
/*
If MAX(expr) is the first part of a key or if all previous
parts of the key is found in the COND, then we can use
indexes to find the key.
*/
Item *expr=item_sum->args[0];
if (expr->real_item()->type() == Item::FIELD_ITEM)
{
byte key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
uint range_fl, prefix_len;
ref.key_buff= key_buff;
Item_field *item_field= (Item_field*) (expr->real_item());
TABLE *table= item_field->field->table;
/*
Look for a partial key that can be used for optimization.
If we succeed, ref.key_length will contain the length of
this key, while prefix_len will contain the length of
the beginning of this key without field used in MAX().
Type of range for the key part for this field will be
returned in range_fl.
*/
if ((outer_tables & table->map) ||
!find_key_for_maxmin(1, &ref, item_field->field, conds,
&range_fl, &prefix_len))
{
const_result= 0;
break;
}
error= table->file->ha_index_init((uint) ref.key, 1);
if (!ref.key_length)
error= table->file->index_last(table->record[0]);
else
error= table->file->index_read(table->record[0], key_buff,
ref.key_length,
range_fl & NEAR_MAX ?
HA_READ_BEFORE_KEY :
HA_READ_PREFIX_LAST_OR_PREV);
if (!error && reckey_in_range(1, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
if (table->key_read)
{
table->key_read=0;
table->file->extra(HA_EXTRA_NO_KEYREAD);
}
table->file->ha_index_end();
if (error)
{
if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
return -1; // No rows matching WHERE
/* HA_ERR_LOCK_DEADLOCK or some other error */
table->file->print_error(error, MYF(0));
return(error);
}
removed_tables|= table->map;
}
else if (!expr->const_item() || !is_exact_count)
{
/*
The optimization is not applicable in both cases:
(a) 'expr' is a non-constant expression. Then we can't
replace 'expr' by a constant.
(b) 'expr' is a costant. According to ANSI, MIN/MAX must return
NULL if the query does not return any rows. Thus, if we are not
able to determine if the query returns any rows, we can't apply
the optimization and replace MIN/MAX with a constant.
*/
const_result= 0;
break;
}
if (!count)
{
/* If count != 1, then we know that is_exact_count == TRUE. */
((Item_sum_max*) item_sum)->clear(); /* Set to NULL. */
}
else
((Item_sum_max*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_max*) item_sum)->make_const();
recalc_const_item= 1;
break;
}
default:
const_result= 0;
break;
}
}
else if (const_result)
{
if (recalc_const_item)
item->update_used_tables();
if (!item->const_item())
const_result= 0;
}
}
/*
If we have a where clause, we can only ignore searching in the
tables if MIN/MAX optimisation replaced all used tables
We do not use replaced values in case of:
SELECT MIN(key) FROM table_1, empty_table
removed_tables is != 0 if we have used MIN() or MAX().
*/
if (removed_tables && used_tables != removed_tables)
const_result= 0; // We didn't remove all tables
return const_result;
}
/*
Test if the predicate compares a field with constants
SYNOPSIS
simple_pred()
func_item Predicate item
args out: Here we store the field followed by constants
inv_order out: Is set to 1 if the predicate is of the form
'const op field'
RETURN
0 func_item is a simple predicate: a field is compared with
constants
1 Otherwise
*/
bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
{
Item *item;
*inv_order= 0;
switch (func_item->argument_count()) {
case 0:
/* MULT_EQUAL_FUNC */
{
Item_equal *item_equal= (Item_equal *) func_item;
Item_equal_iterator it(*item_equal);
args[0]= it++;
if (it++)
return 0;
if (!(args[1]= item_equal->get_const()))
return 0;
}
break;
case 1:
/* field IS NULL */
item= func_item->arguments()[0];
if (item->type() != Item::FIELD_ITEM)
return 0;
args[0]= item;
break;
case 2:
/* 'field op const' or 'const op field' */
item= func_item->arguments()[0];
if (item->type() == Item::FIELD_ITEM)
{
args[0]= item;
item= func_item->arguments()[1];
if (!item->const_item())
return 0;
args[1]= item;
}
else if (item->const_item())
{
args[1]= item;
item= func_item->arguments()[1];
if (item->type() != Item::FIELD_ITEM)
return 0;
args[0]= item;
*inv_order= 1;
}
else
return 0;
break;
case 3:
/* field BETWEEN const AND const */
item= func_item->arguments()[0];
if (item->type() == Item::FIELD_ITEM)
{
args[0]= item;
for (int i= 1 ; i <= 2; i++)
{
item= func_item->arguments()[i];
if (!item->const_item())
return 0;
args[i]= item;
}
}
else
return 0;
}
return 1;
}
/*
Check whether a condition matches a key to get {MAX|MIN}(field):
SYNOPSIS
matching_cond()
max_fl in: Set to 1 if we are optimising MAX()
ref in/out: Reference to the structure we store the key value
keyinfo in Reference to the key info
field_part in: Pointer to the key part for the field
cond in WHERE condition
key_part_used in/out: Map of matchings parts
range_fl in/out: Says whether including key will be used
prefix_len out: Length of common key part for the range
where MAX/MIN is searched for
DESCRIPTION
For the index specified by the keyinfo parameter, index that
contains field as its component (field_part), the function
checks whether the condition cond is a conjunction and all its
conjuncts referring to the columns of the same table as column
field are one of the following forms:
- f_i= const_i or const_i= f_i or f_i is null,
where f_i is part of the index
- field {<|<=|>=|>|=} const or const {<|<=|>=|>|=} field
- field between const1 and const2
RETURN
0 Index can't be used.
1 We can use index to get MIN/MAX value
*/
static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
KEY_PART_INFO *field_part, COND *cond,
key_part_map *key_part_used, uint *range_fl,
uint *prefix_len)
{
if (!cond)
return 1;
Field *field= field_part->field;
if (!(cond->used_tables() & field->table->map))
{
/* Condition doesn't restrict the used table */
return 1;
}
if (cond->type() == Item::COND_ITEM)
{
if (((Item_cond*) cond)->functype() == Item_func::COND_OR_FUNC)
return 0;
/* AND */
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item= li++))
{
if (!matching_cond(max_fl, ref, keyinfo, field_part, item,
key_part_used, range_fl, prefix_len))
return 0;
}
return 1;
}
if (cond->type() != Item::FUNC_ITEM)
return 0; // Not operator, can't optimize
bool eq_type= 0; // =, <=> or IS NULL
bool noeq_type= 0; // < or >
bool less_fl= 0; // < or <=
bool is_null= 0;
bool between= 0;
switch (((Item_func*) cond)->functype()) {
case Item_func::ISNULL_FUNC:
is_null= 1; /* fall through */
case Item_func::EQ_FUNC:
case Item_func::EQUAL_FUNC:
eq_type= 1;
break;
case Item_func::LT_FUNC:
noeq_type= 1; /* fall through */
case Item_func::LE_FUNC:
less_fl= 1;
break;
case Item_func::GT_FUNC:
noeq_type= 1; /* fall through */
case Item_func::GE_FUNC:
break;
case Item_func::BETWEEN:
between= 1;
break;
case Item_func::MULT_EQUAL_FUNC:
eq_type= 1;
break;
default:
return 0; // Can't optimize function
}
Item *args[3];
bool inv;
/* Test if this is a comparison of a field and constant */
if (!simple_pred((Item_func*) cond, args, &inv))
return 0;
if (inv && !eq_type)
less_fl= 1-less_fl; // Convert '<' -> '>' (etc)
/* Check if field is part of the tested partial key */
byte *key_ptr= ref->key_buff;
KEY_PART_INFO *part;
for (part= keyinfo->key_part;
;
key_ptr+= part++->store_length)
{
if (part > field_part)
return 0; // Field is beyond the tested parts
if (part->field->eq(((Item_field*) args[0])->field))
break; // Found a part od the key for the field
}
bool is_field_part= part == field_part;
if (!(is_field_part || eq_type))
return 0;
key_part_map org_key_part_used= *key_part_used;
if (eq_type || between || max_fl == less_fl)
{
uint length= (key_ptr-ref->key_buff)+part->store_length;
if (ref->key_length < length)
/* Ultimately ref->key_length will contain the length of the search key */
ref->key_length= length;
if (!*prefix_len && part+1 == field_part)
*prefix_len= length;
if (is_field_part && eq_type)
*prefix_len= ref->key_length;
*key_part_used|= (key_part_map) 1 << (part - keyinfo->key_part);
}
if (org_key_part_used != *key_part_used ||
(is_field_part &&
(between || eq_type || max_fl == less_fl) && !cond->val_int()))
{
/*
It's the first predicate for this part or a predicate of the
following form that moves upper/lower bounds for max/min values:
- field BETWEEN const AND const
- field = const
- field {<|<=} const, when searching for MAX
- field {>|>=} const, when searching for MIN
*/
if (is_null)
{
part->field->set_null();
*key_ptr= (byte) 1;
}
else
{
store_val_in_field(part->field, args[between && max_fl ? 2 : 1]);
if (part->null_bit)
*key_ptr++= (byte) test(part->field->is_null());
part->field->get_key_image((char*) key_ptr, part->length, Field::itRAW);
}
if (is_field_part)
{
if (between || eq_type)
*range_fl&= ~(NO_MAX_RANGE | NO_MIN_RANGE);
else
{
*range_fl&= ~(max_fl ? NO_MAX_RANGE : NO_MIN_RANGE);
if (noeq_type)
*range_fl|= (max_fl ? NEAR_MAX : NEAR_MIN);
else
*range_fl&= ~(max_fl ? NEAR_MAX : NEAR_MIN);
}
}
}
else if (eq_type)
{
if (!is_null && !cond->val_int() ||
is_null && !test(part->field->is_null()))
return 0; // Impossible test
}
else if (is_field_part)
*range_fl&= ~(max_fl ? NO_MIN_RANGE : NO_MAX_RANGE);
return 1;
}
/*
Check whether we can get value for {max|min}(field) by using a key.
SYNOPSIS
find_key_for_maxmin()
max_fl in: 0 for MIN(field) / 1 for MAX(field)
ref in/out Reference to the structure we store the key value
field in: Field used inside MIN() / MAX()
cond in: WHERE condition
range_fl out: Bit flags for how to search if key is ok
prefix_len out: Length of prefix for the search range
DESCRIPTION
If where condition is not a conjunction of 0 or more conjuct the
function returns false, otherwise it checks whether there is an
index including field as its k-th component/part such that:
1. for each previous component f_i there is one and only one conjunct
of the form: f_i= const_i or const_i= f_i or f_i is null
2. references to field occur only in conjucts of the form:
field {<|<=|>=|>|=} const or const {<|<=|>=|>|=} field or
field BETWEEN const1 AND const2
3. all references to the columns from the same table as column field
occur only in conjucts mentioned above.
If such an index exists the function through the ref parameter
returns the key value to find max/min for the field using the index,
the length of first (k-1) components of the key and flags saying
how to apply the key for the search max/min value.
(if we have a condition field = const, prefix_len contains the length
of the whole search key)
NOTE
This function may set table->key_read to 1, which must be reset after
index is used! (This can only happen when function returns 1)
RETURN
0 Index can not be used to optimize MIN(field)/MAX(field)
1 Can use key to optimize MIN()/MAX()
In this case ref, range_fl and prefix_len are updated
*/
static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref,
Field* field, COND *cond,
uint *range_fl, uint *prefix_len)
{
if (!(field->flags & PART_KEY_FLAG))
return 0; // Not key field
TABLE *table= field->table;
uint idx= 0;
KEY *keyinfo,*keyinfo_end;
for (keyinfo= table->key_info, keyinfo_end= keyinfo+table->s->keys ;
keyinfo != keyinfo_end;
keyinfo++,idx++)
{
KEY_PART_INFO *part,*part_end;
key_part_map key_part_to_use= 0;
uint jdx= 0;
*prefix_len= 0;
for (part= keyinfo->key_part, part_end= part+keyinfo->key_parts ;
part != part_end ;
part++, jdx++, key_part_to_use= (key_part_to_use << 1) | 1)
{
if (!(table->file->index_flags(idx, jdx, 0) & HA_READ_ORDER))
return 0;
if (field->eq(part->field))
{
ref->key= idx;
ref->key_length= 0;
key_part_map key_part_used= 0;
*range_fl= NO_MIN_RANGE | NO_MAX_RANGE;
if (matching_cond(max_fl, ref, keyinfo, part, cond,
&key_part_used, range_fl, prefix_len) &&
!(key_part_to_use & ~key_part_used))
{
if (!max_fl && key_part_used == key_part_to_use && part->null_bit)
{
/*
SELECT MIN(key_part2) FROM t1 WHERE key_part1=const
If key_part2 may be NULL, then we want to find the first row
that is not null
*/
ref->key_buff[ref->key_length]= 1;
ref->key_length+= part->store_length;
*range_fl&= ~NO_MIN_RANGE;
*range_fl|= NEAR_MIN; // > NULL
}
/*
The following test is false when the key in the key tree is
converted (for example to upper case)
*/
if (field->part_of_key.is_set(idx))
{
table->key_read= 1;
table->file->extra(HA_EXTRA_KEYREAD);
}
return 1;
}
}
}
}
return 0;
}
/*
Check whether found key is in range specified by conditions
SYNOPSIS
reckey_in_range()
max_fl in: 0 for MIN(field) / 1 for MAX(field)
ref in: Reference to the key value and info
field in: Field used the MIN/MAX expression
cond in: WHERE condition
range_fl in: Says whether there is a condition to to be checked
prefix_len in: Length of the constant part of the key
RETURN
0 ok
1 WHERE was not true for the found row
*/
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint range_fl, uint prefix_len)
{
if (key_cmp_if_same(field->table, ref->key_buff, ref->key, prefix_len))
return 1;
if (!cond || (range_fl & (max_fl ? NO_MIN_RANGE : NO_MAX_RANGE)))
return 0;
return maxmin_in_range(max_fl, field, cond);
}
/*
Check whether {MAX|MIN}(field) is in range specified by conditions
SYNOPSIS
maxmin_in_range()
max_fl in: 0 for MIN(field) / 1 for MAX(field)
field in: Field used the MIN/MAX expression
cond in: WHERE condition
RETURN
0 ok
1 WHERE was not true for the found row
*/
static int maxmin_in_range(bool max_fl, Field* field, COND *cond)
{
/* If AND/OR condition */
if (cond->type() == Item::COND_ITEM)
{
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item= li++))
{
if (maxmin_in_range(max_fl, field, item))
return 1;
}
return 0;
}
if (cond->used_tables() != field->table->map)
return 0;
bool less_fl= 0;
switch (((Item_func*) cond)->functype()) {
case Item_func::BETWEEN:
return cond->val_int() == 0; // Return 1 if WHERE is false
case Item_func::LT_FUNC:
case Item_func::LE_FUNC:
less_fl= 1;
case Item_func::GT_FUNC:
case Item_func::GE_FUNC:
{
Item *item= ((Item_func*) cond)->arguments()[1];
/* In case of 'const op item' we have to swap the operator */
if (!item->const_item())
less_fl= 1-less_fl;
/*
We only have to check the expression if we are using an expression like
SELECT MAX(b) FROM t1 WHERE a=const AND b>const
not for
SELECT MAX(b) FROM t1 WHERE a=const AND b<const
*/
if (max_fl != less_fl)
return cond->val_int() == 0; // Return 1 if WHERE is false
return 0;
}
case Item_func::EQ_FUNC:
case Item_func::EQUAL_FUNC:
break;
default: // Keep compiler happy
DBUG_ASSERT(1); // Impossible
break;
}
return 0;
}
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