Table: The hint applies to a specific table. Index: The hint applies to the use of a specific index. hint的语法 /*+ ... */ 注意三个点的前后都有一个空格。语法树都比较好看,举例几个比较难懂的语法。 #QB_NAME() 的用法。 可以把一个复杂的查询,划分成多个 query_block,然后再针对每个 qb进...
$ mysqldump test t1 -- [Version and host comments] /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */; -- [More version-specific comments to save options for restore] -- -- Table structure for table `t1` -- DROP TABLE IF EXISTS `t1`; /*!40101 SET @saved_cs_client...
代码语言:javascript 复制 SELECTci.CountryCode,co.NameASCountry,ci.NameASCity,ci.DistrictFROMworld.country coIGNOREINDEX(Primary)INNERJOINworld.city ciIGNOREINDEX(CountryCode)ONci.CountryCode=co.CodeWHEREco.Continent='Asia';SELECT*FROMworld.cityUSEINDEXFORORDERBY(Primary)WHERECountryCode='AUS'ORDERBYID...
'user', 'p4ssword'); my $sth = $dbh->prepare('SELECT * FROM HUGE_TABLE', { mysql_use_result => 1 }); $sth->execute(); while ( my $row = $sth->fetchrow_array() ) { # Do something with result }
To find theMIN()orMAX()value for a specific indexed columnkey_col. This is optimized by a preprocessor that checks whether you are usingWHEREkey_part_N=constanton all key parts that occur beforekey_colin the index. In this case, MySQL does a single key lookup for eachMIN()orMAX()expre...
Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, ...
When to use index? Index statement Introduction to Index 什么是索引? "Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows." -- MySQL ...
Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, ...
使用覆盖索引(Extra列中的“Using index”)避免行访问,并在从索引检索每个结果后过滤掉不匹配的行。这发生在服务器层,但不需要从表中读取行。 从表中检索行,然后过滤不匹配的行(“在Extra列中使用 where”)。这发生在服务器层,需要服务器在过滤行之前从表中读取行。
I had same problem too. Some other facts: 1- It didn’t work even when I forced queries to use a specific index using USE INDEX option. 2- When I change the query from: SELECT * FROM table1 WHERE field IN (SELECT field FROM table2 WHERE ...) to: SELECT * FROM table1 WHERE fi...