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Take into account that table scans may use indexes

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This commit is contained in:
monty@hundin.mysql.fi 2002-01-30 16:07:11 +02:00
parent 869b7914be
commit c396824b2a
5 changed files with 22 additions and 7 deletions
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3
Docs/manual.texi
View File

@ -48374,6 +48374,9 @@ Our TODO section contains what we plan to have in 4.0. @xref{TODO MySQL 4.0}.
@itemize @bullet
@item
Don't use table scan with BerkeleyDB and InnoDB tables when we can use
an index that covers the whole row.
@item
Added sql-mode flag @code{NO_UNSIGNED_SUBTRACTION} to disable unsigned
arithmetic rules when it comes to subtraction. (This will make MySQL 4.0
behave more closely to 3.23 with @code{UNSIGNED} columns).

2
sql/ha_berkeley.h
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@ -92,7 +92,7 @@ class ha_berkeley: public handler
HA_NULL_KEY | HA_HAVE_KEY_READ_ONLY |
HA_BLOB_KEY | HA_NOT_EXACT_COUNT |
HA_PRIMARY_KEY_IN_READ_INDEX | HA_DROP_BEFORE_CREATE |
HA_AUTO_PART_KEY),
HA_AUTO_PART_KEY | HA_TABLE_SCAN_ON_INDEX),
changed_rows(0),last_dup_key((uint) -1),version(0),using_ignore(0)
{
}

3
sql/ha_innodb.h
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@ -84,7 +84,8 @@ class ha_innobase: public handler
HA_NO_WRITE_DELAYED |
HA_PRIMARY_KEY_IN_READ_INDEX |
HA_DROP_BEFORE_CREATE | HA_NOT_READ_PREFIX_LAST |
HA_NO_PREFIX_CHAR_KEYS),
HA_NO_PREFIX_CHAR_KEYS |
HA_TABLE_SCAN_ON_INDEX),
last_dup_key((uint) -1),
start_of_scan(0)
{

12
sql/handler.h
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@ -42,16 +42,13 @@
#define HA_ADMIN_INVALID -5
/* Bits in bas_flag to show what database can do */
#define HA_READ_NEXT 1 /* Read next record with same key */
#define HA_READ_PREV 2 /* Read prev. record with same key */
#define HA_READ_ORDER 4 /* Read through record-keys in order */
#define HA_READ_RND_SAME 8 /* Read RND-record to KEY-record
(To update with RND-read) */
#define HA_KEYPOS_TO_RNDPOS 16 /* ha_info gives pos to record */
#define HA_LASTKEY_ORDER 32 /* Next record gives next record
according last record read (even
if database is updated after read) */
#define HA_TABLE_SCAN_ON_INDEX 32 /* No separate data/index file */
#define HA_REC_NOT_IN_SEQ 64 /* ha_info don't return recnumber;
It returns a position to ha_r_rnd */
#define HA_ONLY_WHOLE_INDEX 128 /* Can't use part key searches */
@ -78,6 +75,13 @@
#define HA_CAN_FULLTEXT (HA_NO_PREFIX_CHAR_KEYS*2)
#define HA_CAN_SQL_HANDLER (HA_CAN_FULLTEXT*2)
/* Old not used flags */
/*
Next record gives next record according last record read (even
if database is updated after read)
*/
#define HA_LASTKEY_ORDER 0
/* Parameters for open() (in register form->filestat) */
/* HA_GET_INFO does an implicit HA_ABORT_IF_LOCKED */

9
sql/sql_select.cc
View File

@ -1939,10 +1939,17 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
/*
Don't test table scan if it can't be better.
Prefer key lookup if we would use the same key for scanning.
Don't do a table scan on InnoDB tables, if we can read the used
parts of the row from any of the used index.
This is because table scans uses index and we would not win
anything by using a table scan.
*/
if ((records >= s->found_records || best > s->read_time) &&
!(s->quick && best_key && s->quick->index == best_key->key &&
best_max_key_part >= s->table->quick_key_parts[best_key->key]))
best_max_key_part >= s->table->quick_key_parts[best_key->key]) &&
!((s->table->file->option_flag() & HA_TABLE_SCAN_ON_INDEX) &&
s->table->used_keys && best_key))
{ // Check full join
if (s->on_expr)
{