3 Suggestions on database model design/ performance 0 What does select * from table where column * 'value'; do? 0 How to prevent a record from being affected by the ORDER BY RAND statement in MYSQL 4 Select only rows where all values in a column match a value for an id H...
SELECT[ALL | DISTINCT | DISTINCTROW ] [HIGH_PRIORITY] [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT] [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS] select_expr [, select_expr ...] [FROMtable_references [PARTITION partition_list] [WHEREwhere_condition] [GRO...
SET @sql = CONCAT('SELECT ', (SELECT REPLACE(GROUP_CONCAT(COLUMN_NAME), '<columns_to_omit>,', '') FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = '<table>' AND TABLE_SCHEMA = '<database>'), ' FROM <table>'); PREPARE stmt1 FROM @sql; EXECUTE stmt1; Replacing <table>, <d...
select * from user_customer where first_name='123' and last_name='456'; explain select * from migrations,user_customer where migrations.batch=user_customer.uid and cid>1\G; eq_ref:通常出现在多表的join查询,对于对于前表的每一个结果,都只能匹配到后表的一行结果,并且查询的比较操作是=,查询效率...
SUBQUERY 子查询中的第一个SELECT.DEPENDENT SUBQUERY 子查询中的第一个SELECT，取决于外面的查询DERIVED ...
union all 不去重复,union去重复,union使用了临时表,应尽量避免使用临时表 10. 复合索引 对于复合索引,如果单独使用右边的索引字段作为条件时不走索引的。即复合索引如果不满足最左原则leftmost不会走复合索引 11. 覆盖索引 覆盖索引是select的数据列只用从索引中就能够取得,不必读取数据行,换句话说查询列要被所建的...
select语句,首先,看看select语句的用法,很多网站的注入点都是从select入手的: SELECT[ALL|DISTINCT|DISTINCTROW][HIGH_PRIORITY][STRAIGHT_JOIN][SQL_SMALL_RESULT][SQL_BIG_RESULT][SQL_BUFFER_RESULT][SQL_CACHE|SQL_NO_CACHE][SQL_CALC_FOUND_ROWS]select_expr[,select_expr...][FROMtable_references[PARTITION...
Date: June 27, 2007 04:41AM As sub? I need to look in table 1 and pick all those records not in table in 2 I know that table 2 has 51000 records and table 1 has 65000. I want to see the 14000 in table 1 that doesn't have a match in table 2 ...
SELECTname,ageFROMpersonWHEREage>(SELECTageFROMpersonWHEREname='张三'); 返回一组值 如果子查询的返回值不止一个,而是一个集合时,则不能直接使用比较运算符,可以在比较运算符和子查询之间插入IN、ANY、SOME、ALL, 或者EXISTS。 IN,用于where子句中用来判断查询的表达式是否在子查询集合中,返回满足IN列表中的记录...
unique_subquery 这种连接方式在某种情况下会代替eq_ref,如value IN (SELECT primary_key FROM single_table WHERE some_expr),这种方式使用索引查询功能代替子查询,以获得更好的执行效率。 index_subquery 这种连接方式类似unique_subquery。它会代替IN子查询,但是它适用于非unique索引的子查询,如value IN (SELECT ke...