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Fulltext manual changed, MERGE bug fixed

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serg@serg.mysql.com
2001-05-16 23:06:30 +02:00
parent 4e04aa4abd
commit b6138af000
7 changed files with 106 additions and 97 deletions
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117
Docs/manual.texi
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@ -29233,42 +29233,36 @@ index.
Full-text search is performed with the @code{MATCH} function.
@example
mysql> CREATE TABLE t (a VARCHAR(200), b TEXT, FULLTEXT (a,b));
mysql> CREATE TABLE articles (
-> id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
-> title VARCHAR(200),
-> body TEXT,
-> FULLTEXT (title,body)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO t VALUES
-> ('MySQL has now support', 'for full-text search'),
-> ('Full-text indexes', 'are called collections'),
-> ('Only MyISAM tables','support collections'),
-> ('Function MATCH ... AGAINST()','is used to do a search'),
-> ('Full-text search in MySQL', 'implements vector space model');
mysql> INSERT INTO articles VALUES
-> (0,'MySQL Tutorial', 'DBMS stands for DataBase Management ...'),
-> (0,'How To Use MySQL Efficiently', 'After you went through a ...'),
-> (0,'Optimizing MySQL','In this tutorial we will show how to ...'),
-> (0,'1001 MySQL Trick','1. Never run mysqld as root. 2. Normalize ...'),
-> (0,'MySQL vs. YourSQL', 'In the following database comparison we ...'),
-> (0,'MySQL Security', 'When configured properly, MySQL could be ...');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM t WHERE MATCH (a,b) AGAINST ('MySQL');
+---------------------------+-------------------------------+
| a | b |
+---------------------------+-------------------------------+
| MySQL has now support | for full-text search |
| Full-text search in MySQL | implements vector-space-model |
+---------------------------+-------------------------------+
mysql> SELECT * FROM articles WHERE MATCH (title,body) AGAINST ('database');
+----+-------------------+---------------------------------------------+
| id | title | body |
+----+-------------------+---------------------------------------------+
| 5 | MySQL vs. YourSQL | In the following database comparison we ... |
| 1 | MySQL Tutorial | DBMS stands for DataBase Management ... |
+----+-------------------+---------------------------------------------+
2 rows in set (0.00 sec)
mysql> SELECT *,MATCH a,b AGAINST ('collections support') as x FROM t;
+------------------------------+-------------------------------+--------+
| a | b | x |
+------------------------------+-------------------------------+--------+
| MySQL has now support | for full-text search | 0.3834 |
| Full-text indexes | are called collections | 0.3834 |
| Only MyISAM tables | support collections | 0.7668 |
| Function MATCH ... AGAINST() | is used to do a search | 0 |
| Full-text search in MySQL | implements vector space model | 0 |
+------------------------------+-------------------------------+--------+
5 rows in set (0.00 sec)
@end example
The function @code{MATCH} matches a natural language query @code{AGAINST}
a text collection (which is simply the columns that are covered by a
a text collection (which is simply the set of columns covered by a
@code{FULLTEXT} index). For every row in a table it returns relevance -
a similarity measure between the text in that row (in the columns that are
part of the collection) and the query. When it is used in a @code{WHERE}
@ -29279,10 +29273,51 @@ number of words in the row, the number of unique words in that row, the
total number of words in the collection, and the number of documents (rows)
that contain a particular word.
MySQL uses a very simple parser to split text into words. A ``word'' is
any sequence of letters, numbers, @samp{'}, and @samp{_}. Any ``word''
that is present in the stopword list or just too short (3 characters
or less) is ignored.
The above is a basic example of using @code{MATCH} function. Rows are
returned with relevance decreasing.
@example
mysql> SELECT id,MATCH (title,body) AGAINST ('Tutorial') FROM articles;
+----+-----------------------------------------+
| id | MATCH (title,body) AGAINST ('Tutorial') |
+----+-----------------------------------------+
| 1 | 0.64840710366884 |
| 2 | 0 |
| 3 | 0.66266459031789 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
+----+-----------------------------------------+
5 rows in set (0.00 sec)
@end example
This example shows how to retrieve the relevances. As neither @code{WHERE}
nor @code{ORDER BY} clauses are present, returned rows are not ordered.
@example
mysql> SELECT id, body, MATCH (title,body) AGAINST (
-> 'Security implications of running MySQL as root') AS score
-> FROM articles WHERE MATCH (title,body) AGAINST
-> ('Security implications of running MySQL as root');
+----+-----------------------------------------------+-----------------+
| id | body | score |
+----+-----------------------------------------------+-----------------+
| 4 | 1. Never run mysqld as root. 2. Normalize ... | 1.5055546709332 |
| 6 | When configured properly, MySQL could be ... | 1.31140957288 |
+----+-----------------------------------------------+-----------------+
2 rows in set (0.00 sec)
@end example
This is more complex example - the query returns the relevance and still
sorts the rows with relevance decreasing. To achieve it one should specify
@code{MATCH} twice. Note, that this will cause no additional overhead, as
@strong{MySQL} optimizer will notice that these two @code{MATCH} calls are
identical and will call full-text search code only once.
@strong{MySQL} uses a very simple parser to split text into words. A
``word'' is any sequence of letters, numbers, @samp{'}, and @samp{_}. Any
``word'' that is present in the stopword list or just too short (3
characters or less) is ignored.
Every correct word in the collection and in the query is weighted,
according to its significance in the query or collection. This way, a
@ -29297,17 +29332,22 @@ carefully tuned this way). For very small tables, word distribution
does not reflect adequately their semantical value, and this model
may sometimes produce bizarre results.
For example, search for the word "search" will produce no results in the
above example. Word "search" is present in more than half of rows, and
as such, is effectively treated as a stopword (that is, with semantical value
zero). It is, really, the desired behavior - a natural language query
should not return every other row in 1GB table.
@example
mysql> SELECT * FROM articles WHERE MATCH (title,body) AGAINST ('MySQL');
Empty set (0.00 sec)
@end example
Search for the word @code{MySQL} produces no results in the above example.
Word @code{MySQL} is present in more than half of rows, and as such, is
effectively treated as a stopword (that is, with semantical value zero).
It is, really, the desired behavior - a natural language query should not
return every second row in 1GB table.
A word that matches half of rows in a table is less likely to locate relevant
documents. In fact, it will most likely find plenty of irrelevant documents.
We all know this happens far too often when we are trying to find something on
the Internet with a search engine. It is with this reasoning that such rows
have been assigned a low semantical value in @strong{a particular dataset}.
have been assigned a low semantical value in @strong{this particular dataset}.
@menu
* Fulltext Fine-tuning::
@ -44120,6 +44160,9 @@ not yet 100% confident in this code.
@appendixsubsec Changes in release 3.23.38
@itemize @bullet
@item
Fixed a bug when @code{SELECT} from @code{MERGE} table
sometimes results in incorrectly ordered rows.
@item
Fixed a bug in @code{REPLACE()} when using the ujis character set.
@item
Applied Sleepycat BDB patches 3.2.9.1 and 3.2.9.2.

1
myisammrg/mymrgdef.h
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@ -29,4 +29,3 @@ extern pthread_mutex_t THR_LOCK_open;
#endif
int _myrg_init_queue(MYRG_INFO *info,int inx,enum ha_rkey_function search_flag);
int _myrg_finish_scan(MYRG_INFO *info, int inx, enum ha_rkey_function type);

11
myisammrg/myrg_rkey.c
View File

@ -44,7 +44,6 @@ int myrg_rkey(MYRG_INFO *info,byte *record,int inx, const byte *key,
MYRG_TABLE *table;
MI_INFO *mi;
int err;
byte *buf=((search_flag == HA_READ_KEY_EXACT) ? record: 0);
LINT_INIT(key_buff);
LINT_INIT(pack_key_length);
@ -57,14 +56,14 @@ int myrg_rkey(MYRG_INFO *info,byte *record,int inx, const byte *key,
if (table == info->open_tables)
{
err=mi_rkey(mi,buf,inx,key,key_len,search_flag);
err=mi_rkey(mi,0,inx,key,key_len,search_flag);
key_buff=(byte*) mi->lastkey+mi->s->base.max_key_length;
pack_key_length=mi->last_rkey_length;
}
else
{
mi->use_packed_key=1;
err=mi_rkey(mi,buf,inx,key_buff,pack_key_length,search_flag);
err=mi_rkey(mi,0,inx,key_buff,pack_key_length,search_flag);
mi->use_packed_key=0;
}
info->last_used_table=table+1;
@ -78,12 +77,6 @@ int myrg_rkey(MYRG_INFO *info,byte *record,int inx, const byte *key,
/* adding to queue */
queue_insert(&(info->by_key),(byte *)table);
/* if looking for KEY_EXACT, return first matched now */
if (buf)
{
info->current_table=table;
return 0;
}
}
if (!info->by_key.elements)

45
myisammrg/myrg_rnext.c
View File

@ -29,7 +29,11 @@ int myrg_rnext(MYRG_INFO *info, byte *buf, int inx)
if ((err=mi_rnext(info->current_table->table,NULL,inx)))
{
if (err == HA_ERR_END_OF_FILE)
{
queue_remove(&(info->by_key),0);
if (!info->by_key.elements)
return HA_ERR_END_OF_FILE;
}
else
return err;
}
@ -40,48 +44,7 @@ int myrg_rnext(MYRG_INFO *info, byte *buf, int inx)
queue_replaced(&(info->by_key));
}
/* next, let's finish myrg_rkey's initial scan */
if ((err=_myrg_finish_scan(info, inx, HA_READ_KEY_OR_NEXT)))
return err;
if (!info->by_key.elements)
return HA_ERR_END_OF_FILE;
/* now, mymerge's read_next is as simple as one queue_top */
mi=(info->current_table=(MYRG_TABLE *)queue_top(&(info->by_key)))->table;
return mi_rrnd(mi,buf,mi->lastpos);
}
/* let's finish myrg_rkey's initial scan */
int _myrg_finish_scan(MYRG_INFO *info, int inx, enum ha_rkey_function type)
{
int err;
MYRG_TABLE *table=info->last_used_table;
if (table < info->end_table)
{
MI_INFO *mi= table[-1].table;
byte *key_buff=(byte*) mi->lastkey+mi->s->base.max_key_length;
uint pack_key_length= mi->last_rkey_length;
for (; table < info->end_table ; table++)
{
mi=table->table;
mi->use_packed_key=1;
err=mi_rkey(mi,NULL,inx,key_buff,pack_key_length,type);
mi->use_packed_key=0;
if (err)
{
if (err == HA_ERR_KEY_NOT_FOUND) /* If end of file */
continue;
return err;
}
/* Found here, adding to queue */
queue_insert(&(info->by_key),(byte *) table);
}
/* All tables are now used */
info->last_used_table=table;
}
return 0;
}

13
myisammrg/myrg_rprev.c
View File

@ -29,7 +29,11 @@ int myrg_rprev(MYRG_INFO *info, byte *buf, int inx)
if ((err=mi_rprev(info->current_table->table,NULL,inx)))
{
if (err == HA_ERR_END_OF_FILE)
{
queue_remove(&(info->by_key),0);
if (!info->by_key.elements)
return HA_ERR_END_OF_FILE;
}
else
return err;
}
@ -40,16 +44,7 @@ int myrg_rprev(MYRG_INFO *info, byte *buf, int inx)
queue_replaced(&(info->by_key));
}
/* next, let's finish myrg_rkey's initial scan */
if ((err=_myrg_finish_scan(info, inx, HA_READ_KEY_OR_PREV)))
return err;
if (!info->by_key.elements)
return HA_ERR_END_OF_FILE;
/* now, mymerge's read_prev is as simple as one queue_top */
mi=(info->current_table=(MYRG_TABLE *)queue_top(&(info->by_key)))->table;
return mi_rrnd(mi,buf,mi->lastpos);
}

3
mysql-test/r/merge.result
View File

@ -127,3 +127,6 @@ t3 CREATE TABLE `t3` (
`othr` int(11) NOT NULL default '0'
) TYPE=MRG_MyISAM UNION=(t1,t2)
a
a b
1 1
1 2

13
mysql-test/t/merge.test
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@ -96,3 +96,16 @@ drop table t3,t2,t1;
create table t1 (a int not null) type=merge;
select * from t1;
drop table t1;
#
# Bug found by Monty.
#
drop table if exists t3, t2, t1;
create table t1 (a int not null, b int not null, key(a,b));
create table t2 (a int not null, b int not null, key(a,b));
create table t3 (a int not null, b int not null, key(a,b)) TYPE=MERGE UNION=(t1,t2);
insert into t1 values (1,2),(2,1),(0,0),(4,4),(5,5),(6,6);
insert into t2 values (1,1),(2,2),(0,0),(4,4),(5,5),(6,6);
flush tables;
select * from t3 where a=1 order by b limit 2;