事实上,sql并不是按照我们的书写顺序来从前往后、左往右依次执行的,它是按照固定的顺序解析的,主要的作用就是从上一个阶段的执行返回结果来提供给下一阶段使用,sql在执行的过程中会有不同的临时中间表,一般是按照如下顺序: 例子: select distinct s.id from T t join S s on t.id=s.id where t.name="Y...
Unlocking the Power of JavaScript in MySQL: Creating Stored Programs with Ease On-Demand What’s New in MySQL Monitoring with Oracle Enterprise Manager Plugin On-Demand Transforming Government Operations with Open-Source Innovation: Unlock the Power of MySQL Enterprise ...
在正式执行 SQL 查询语句之前, MySQL 会先对 SQL 语句做解析,这个工作交由解析器来完成。解析器可以将输入的 SQL 语句转换为计算机可以理解的形式(语法树,Syntax Tree)。 解析器会做如下两件事情: 词法解析:MySQL 会根据输入的字符串识别出关键字出来,构建出 SQL 语法树; 语法解析:根据词法分析的结果,语法分析...
JOIN:添加外部行,如果指定了LEFT JOIN(LEFT OUTER JOIN),则先遍历一遍左表的每一行,其中不在vt2的行会被插入到vt2,该行的剩余字段将被填充为NULL,形成vt3;如果指定了RIGHT JOIN也是同理。但如果指定的是INNER JOIN,则不会添加外部行,上述插入过程被忽略,vt2=vt3(所以INNER JOIN的过滤条件放在ON或WHERE里 执行...
13.7.5.17 SHOW ENGINES Syntax 13.7.5.18 SHOW ERRORS Syntax 13.7.5.19 SHOW EVENTS Syntax 13.7.5.20 SHOW FUNCTION CODE Syntax 13.7.5.21 SHOW FUNCTION STATUS Syntax 13.7.5.22 SHOW GRANTS Syntax 13.7.5.23 SHOW INDEX Syntax 13.7.5.24 SHOW MASTER STATUS Syntax ...
14.2.9.2 JOIN Syntax In MySQL,JOIN,CROSS JOIN, andINNER JOINare syntactic equivalents (they can replace each other). Generally, you should use theONclause for conditions that specify how to join tables, and theWHEREclause to restrict which rows you want in the result set. ...
mysql> elect * from t where ID=1;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 ‘elect * from t where ID=1’ at line 1 4、优化器（怎么做）优化器是在表里面有多个索引的时候...
这个sql是用来查询出c表中有h表中无的记录,所以想到了用left join的特性(返回左边全部记录,右表不满足匹配条件的记录对应行返回null)来满足需求,不料这个查询非常慢。先来看查询计划: rows代表这个步骤相对上一步结果的每一行需要扫描的行数,可以看到这个sql需要扫描的行数为35773*8134,非常大的一个数字。本来c和...
SQL JOIN syntax ??Posted by: dan bloch Date: March 29, 2006 11:49AM the query browser says: "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 '[transAction] ON transActionDtl.transActionID = ...
select distinct s.id from T t join S s on t.id=s.id where t.name="Yrion" group by t.mobile having count(*)>2 order by s.create_time limit 5; 这里有几个需要注意的地方: 1、SQL语句是从FROM开始执行的,而不是SELECT。MySQL在执行SQL查询语句的时,首先...