使用了执行计划EXPLAIN 以下SQL语句 EXPLAIN SELECT SQL_NO_CACHE * FROM emp WHERE emp.age=30...EXPLAIN SELECT SQL_NO_CACHE * FROM emp WHERE emp.age=30 and deptid=4 EXPLAIN...SELECT SQL_NO_CACHE * FROM emp WHERE emp.age=30 and deptid=4 AND emp.name = 'abcd' 可以通过建立了 索引，SQL如下...EXPLAIN SELECT SQL_NO_CACHE * FROM emp WHERE age=30; EXPLAIN SELECT SQL_NO_CACHE * FROM emp WHERE LEFT...* FROM emp WHERE emp.age=30 and deptid=5 AND emp.name = 'abcd'; explain SELECT SQL_NO_CACHE * FROM
计算、函数、类型转换(自动或手动)导致索引失效 创建索引 CREATE INDEX idx_name ON student(NAME); 索引优化生效 EXPLAIN SELECT SQL_NO_CACHE...* FROM student WHERE student.name LIKE 'abc%'; 索引优化失效 EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE...（假设name字段上设置有索引） # 未使用到索引 EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE name=123; # 使用到索引 EXPLAIN...SELECT SQL_NO_CACHE * FROM student WHERE name='123' name=123发生类型转换，索引失效。 ...= 或者)索引失效 is null可以使用索引，is not null无法使用索引 EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE age IS
意思是说查询时不适用缓存 SELECT SQL_NO_CACHE count(id) FROM `datetime_test` WHERE d_int >400000 AND d_int<600000...查询花费 0.0780 秒 SELECT SQL_NO_CACHE count(id) FROM `datetime_test` WHERE d_int>UNIX_TIMESTAMP('1970-...>'1970-01-05 23:06:40' AND d_datetime<'1970-01-08 06:40:00' 查询花费 0.1370 秒 SELECT SQL_NO_CACHE count(...2.2 MyISAM 引擎有索引下的 dint/dtimestamp/d_datetime 2.2.1 int 类型是否调用 UNIX_TIMESTAMP 优化对比 SELECT SQL_NO_CACHE...2.2.2 timestamp 类型是否调用 UNIX_TIMESTAMP 优化对比 SELECT SQL_NO_CACHE count(id) FROM `datetime_test` WHERE
EXPLAIN SELECT SQL_NO_CACHE * FROM `type` LEFT JOIN book ON type.card = book.card; 执行结果如下。...CREATE INDEX Y ON book(card); #【被驱动表】，可以避免全表扫描 EXPLAIN SELECT SQL_NO_CACHE * FROM `type` LEFT JOIN book...DROP INDEX Y ON book; EXPLAIN SELECT SQL_NO_CACHE * FROM `type` LEFT JOIN book ON type.card = book.card...EXPLAIN SELECT SQL_NO_CACHE * FROM type INNER JOIN book ON type.card=book.card; 结果如下。...DROP INDEX X ON `type`; EXPLAIN SELECT SQL_NO_CACHE * FROM TYPE INNER JOIN book ON type.card=book.card
-----+-----------+-------------+----------+--------+------+------------+---------+ 对比的sql为： select sql_no_cache... max(id) from testtable where number=98; select sql_no_cache id from testtable where number=98 order...by id desc limit 1; 查看执行计划： mysql> explain select sql_no_cache max(id) from testtable where number=...+---------+-------+------+--------------------------+ 1 row in set (0.00 sec) mysql> explain select sql_no_cache... max(id) from testtable where number=98; 需要读取 number=98 的所有行，才能得到最大的id select sql_no_cache id from
OK> 时间: 0.038sselect SQL_NO_CACHE...' and test_timestamp OK> 时间: 0.034sselect SQL_NO_CACHE...count(*) from datetime_test> OK> 时间: 3.898sselect SQL_NO_CACHE count(*) from datetime_test> OK> 时间:...4.152sselect SQL_NO_CACHE count(*) from datetime_test> OK> 时间: 3.17s统计数量count 可以直接使用二级索引，不需要回表性能：bigint
通常情况下我们都这样这样取分页数据 SELECT SQL_NO_CACHE * FROM erp_orders ORDER BY id LIMIT 300000,10; 一般情况下，ORM生成的就是这种语句...可以这样： 先取出主键数据，再取出需要列的数据 SELECT SQL_NO_CACHE * FROM erp_orders o INNER JOIN(SELECT id FROM erp_orders...ORDER BY id LIMIT 300000,10) AS t ON o.id=t.id; 实例测试 erp_orders 表 38万数据 一、通常做法 SELECT SQL_NO_CACHE *...FROM erp_orders ORDER BY id LIMIT 300000,10; 需要约2.169s 二、优化分页 SELECT SQL_NO_CACHE * FROM erp_orders
EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE age=30; EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE...= 'abcd'; SQL_NO_CACHE表示不使用查询缓存。...EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE student.name LIKE 'abc%'; EXPLAIN SELECT SQL_NO_CACHE...EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE age IS NULL; EXPLAIN SELECT SQL_NO_CACHE * FROM student...使用到索引 EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE NAME LIKE 'ab%'; 未使用到索引.
127.0.0.1:40976 | NULL | Query | 16 | executing | SELECT SQL_NO_CACHE...127.0.0.1:42490 | NULL | Query | 1 | executing | SELECT SQL_NO_CACHE...127.0.0.1:42492 | NULL | Query | 1 | executing | SELECT SQL_NO_CACHE...127.0.0.1:42494 | test | Query | 1 | executing | SELECT SQL_NO_CACHE...127.0.0.1:42496 | test | Query | 1 | executing | SELECT SQL_NO_CACHE
test_not_full_char from string_test where test_not_full_char like 'aa%'> OK> 时间: 0.651sselect SQL_NO_CACHE...test_short_varchar from string_test where test_short_varchar like 'aa%'> OK> 时间: 0.698sselect SQL_NO_CACHE...test_long_varchar from string_test where test_long_varchar like 'aa%'> OK> 时间: 0.747sselect SQL_NO_CACHE...test_not_full_char from string_test where test_not_full_char like 'aa%'> OK> 时间: 0.628sselect SQL_NO_CACHE...test_full_char from string_test where test_full_char like 'zz%'> OK> 时间: 0.932sselect SQL_NO_CACHE
禁止缓存 SQL_NO_CACHE 10.6.3. 关闭缓存 set session query_cache_type=off 10.1. 什么是数据库缓存？...禁止缓存 SQL_NO_CACHE 这里我们主要讲怎样禁止缓存，使查询出的结果集不进入缓存。...SELECT SQL_NO_CACHE * FROM table where id=xxxx 下面的用法比较安全，切换到其他数据库也能正常工作 SELECT /*!...40001 SQL_NO_CACHE */ * FROM table set session query_cache_type=on;flush tables;show status like 'qcache_q...%';select sql_no_cache * from member where id=1;show status like 'qcache_q%';select sql_no_cache * from
110条记录，然后在server层丢弃前100条记录取最后10条这样先扫描完再丢弃的记录相当于白找，深分页问题指的就是这种场景（当limit的偏移量过大时会导致性能开销）-- 0.04sselect SQL_NO_CACHE...* from student where age = 18 limit 10;-- 4.049sselect SQL_NO_CACHE * from student where age = 18 limit...select SQL_NO_CACHE * from student where age = 18 and id > 上次查询最大记录 order by id limit 10;但是排序又会带来新的问题...* from student where age = 18 limit 5000,10;-- 游标分页select SQL_NO_CACHE * from student where age = 18...似乎就不需要主键有序了呀使用子查询常用的搭配in，因为分页时子查询数据量也不大，可以使用in来进行查询select SQL_NO_CACHE * from student where age = 18
SQL_NO_CACHE : 服务器不使用查询缓存。它既不检查查询缓存，也不检查结果是否已缓存，也不缓存查询结果。...SELECT SQL_CACHE id, name FROM user; SELECT SQL_NO_CACHE id, name FROM user; 以上就是mysql查询缓存的原理，希望对大家有所帮助
SELECT SQL_NO_CACHE * FROM student WHERE age=30 AND classId=4; EXPLAIN SELECT SQL_NO_CACHE * FROM student...举例 1： EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE student.age=30 AND student.name = 'abcd'; 举例 2...： EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE student.classId=1 AND student.name = 'abcd'; 举例 3：...SELECT SQL_NO_CACHE * FROM student WHERE name='123'; name=123 发生类型转换，索引失效。...使用到索引 EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE name LIKE 'ab%'; 未使用到索引 EXPLAIN SELECT SQL_NO_CACHE
不使用缓存） a.SELECT SQL_NO_CACHE * FROM emp WHERE emp.age=30; b.SELECT SQL_NO_CACHE * FROM emp WHERE emp.age...=30 and deptid=4; c.SELECT SQL_NO_CACHE * FROM emp WHERE emp.age=30 and deptid=4 AND emp.name = ‘abcd...如果系统经常出现的sql如下： SELECT SQL_NO_CACHE * FROM emp WHERE emp.age=30 AND emp.name = ‘abcd’ 或者 SELECT SQL_NO_CACHE...LIKE ‘abc%’ ; SELECT SQL_NO_CACHE * FROM emp WHERE LEFT(emp.name,3) = ‘abc’; ### **添加索引进行测试** CREATE...= 或者)的时候无法使用索引会导致全表扫描 CREATE INDEX idx_name ON emp(NAME) EXPLAIN SELECT SQL_NO_CACHE * FROM emp
`monitor` IS NOT NULL; 举例2：取所有不为班长的同学 不推荐 #查询不为班长的学生信息 EXPLAIN SELECT SQL_NO_CACHE a.* FROM student...EXPLAIN SELECT SQL_NO_CACHE * FROM student ORDER BY age,classid; 很明显是using filesort. 创建索引。...# 会使用索引 （覆盖索引） EXPLAIN SELECT SQL_NO_CACHE age,classid,name,id FROM student ORDER BY age,classid;...EXPLAIN SELECT SQL_NO_CACHE * FROM student ORDER BY age,classid LIMIT 10; 再来，order by 时顺序错误，索引失效 #创建索引...CALL proc_drop_index(`mysql`,`student`) EXPLAIN SELECT SQL_NO_CACHE * FROM student WHERE age = 30 AND
40001 SQL_NO_CACHE */ * FROM `sbtest1`; # Time: 2024-03-20T06:37:00.974869Z # User@Host: backup_user[...40001 SQL_NO_CACHE */ * FROM `sbtest1`; # Time: 2024-03-20T06:37:02.571939Z # User@Host: backup_user[...40001 SQL_NO_CACHE */ * FROM `sbtest1`; # Time: 2024-03-20T06:37:02.754243Z # User@Host: backup_user[...40001 SQL_NO_CACHE */ * FROM `sbtest1`; 场景二 mysqldump 添加备份选项 mysqld-long-query-time 进行数据库备份。
40001 SQL_NO_CACHE */ `id` FROM `db1`....40001 SQL_NO_CACHE */ `id` FROM `db1`....40001 SQL_NO_CACHE */ * FROM `db1`....40001 SQL_NO_CACHE */ `id` FROM `db1`....40001 SQL_NO_CACHE */ `id` FROM `db1`.
select picname, smallimg from pics where user_id = xxx; 优化前 执行查询语句（为了查看真实执行时间，强制不使用缓存） select SQL_NO_CACHE...picname, smallimg from pics where user_id=17853; 执行了10次，平均耗时在40ms左右 使用explain进行分析 explain select SQL_NO_CACHE
32) NOT NULL, PRIMARY KEY (`a`), KEY `bc` (`b`,`c`) ) ENGINE=MyISAM 在第1篇博客中，执行一次查询的语句是： SELECT SQL_NO_CACHE...SQL_CALC_FOUND_ROWS * FROM count_test WHERE b = 555 ORDER BY c LIMIT 5; 执行两次查询的语句是： SELECT SQL_NO_CACHE...* FROM count_test WHERE b = 666 ORDER BY c LIMIT 5; SELECT SQL_NO_CACHE count(*) FROM count_test WHERE...我这里给出一个更全面的示例，我们将查询语句换成以下情形： SELECT SQL_NO_CACHE SQL_CALC_FOUND_ROWS a, b, c FROM count_test WHERE b
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