客户端会将sql语句通过网络连接给mysql。 mysql收到sql语句后,会在分析器中先判断下SQL语句有没有语法错误,比如select,如果少打一个l,写成slect,则会报错You have an error in your SQL syntax;。这个报错对于我这样的手残党来说可以说是很熟悉了。 接下来是优化器,在这里会根据一定的规则选择该用什么索引。 ...
客户端会将sql语句通过网络连接给mysql。 mysql收到sql语句后,会在分析器中先判断下SQL语句有没有语法错误,比如select,如果少打一个l,写成slect,则会报错You have an error in your SQL syntax;。这个报错对于我这样的手残党来说可以说是很熟悉了。 接下来是优化器,在这里会根据一定的规则选择该用什么索引。 ...
mysql> select * fron huanzi; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'fron huanzi' at line 1 mysql> 1. 2. 3. 我们把from写成了fron,分析器做语法分析时识别出这里有问题,...
The following syntax is used to make use of the FORCE INDEX hint. SELECTcol_namesFROMtable_nameFORCEINDEX(index_list)WHEREcondition;Code language:SQL (Structured Query Language)(sql) Note that, you can not combine the FORCE INDEX and the USE INDEX. The FORCE INDEX can consist of one or mo...
[Err] 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘select s.StudentNo,s.StudentName from Student_kb03 s where s.StudentNo in (sel’ at line 14 ...
See the explain syntax page here:http://dev.mysql.com/doc/refman/5.0/en/explain.htmlfor a better explanation of the above :) HTH, Toasty Subject Views Written By Posted FORCE INDEX not working? 5704 Dusty Leary July 17, 2006 07:17PM ...
( id int not null auto_increment, aaa varchar(255) null, PRIMARY KEY (id), INDEX (aaa) ) engine=innodb; This select fails with a syntax error: SELECT * FROM sbv_my_table2 FORCE INDEX(aaa,PRIMARY) ; This select succeeds: SELECT * FROM sbv_my_table2 FORCE INDEX(PRIMARY,aaa) ;How...
This helps with compatibility with some third-party applications, but is not official ODBC syntax. STRAIGHT_JOIN is similar to JOIN, except that the left table is always read before the right table. This can be used for those (few) cases for which the join optimizer processes the tables ...
如果这个字段的值是null,就表示没有索引被用到。这种情况下,就可以检查 where子句中哪些字段那些字段适合增加索引以提高查询的性能。就这样,创建一下索引,然后再用explain 检查一下。详细的查看章节"14.2.2 alter tablesyntax"。想看表都有什么索引,可以通过 show index from tbl_name来看。
which tells the DBMS to parse a clause only if some condition is true. Typical hint classes are "optimizer" and "portability". MySQL has used a variety of things that might be hints: "Index Hint Syntax" e.g. "FORCE INDEX (x)" http://dev.mysql.com/doc/refman/5.0/en/index-hints.ht...