我:Index Condition Pushdown Optimization(索引下推优化) MySQL 5.6 引入了索引下推优化,默认开启,使用 SET optimizer_switch = ‘index_condition_pushdown=off’; 可以将其关闭。官方文档中给的例子和解释如下: people 表中(zipcode,lastname,firstname)构成一个索引 SELECT * FROM people WHERE zipcode=‘95054’...
索引index - 用来快速查找具有特定值的记录 如果没有索引,执行查询时候必须从第一条记录开始扫描整个表的记录,直到符合要求的记录。如果有了索引mysql无需扫描任何记录即可顺序找到目标记录的位置。 简单说来, 索引就是提高查找数据速度,数据量越多,效果越明显。
I made quite a complex View on my MySQL database, and I realized that some queries are slow. My first idea was to add indexes but it's not possible to do on a view so I'm lost on how to improve the performance of my query. ...
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MySQL高级篇之View视图讲解 常见的数据库对象: 一、视图 1.什么是视图 视图是一种虚拟表 ,本身是不具有数据 的,占用很少的内存空间,它是 SQL 中的一个重要概念.视图建立在已有表的基础上, 视图赖以建立的这些表称为基表.视图的创建和删除只影响视图本身,不影响对应的基表。但是当对视图中的数据进行...
MySQL sys Schema Prerequisites for Using the sys Schema Using the sys Schema sys Schema Progress Reporting sys Schema Object Reference sys Schema Object Index sys Schema Tables and Triggers sys Schema Views The host_summary and x$host_summary Views The host_summary_by_file_io and x$...
MySQL sys Schema Prerequisites for Using the sys Schema Using the sys Schema sys Schema Progress Reporting sys Schema Object Reference sys Schema Object Index sys Schema Tables and Triggers sys Schema Views The host_summary and x$host_summary Views The host_summary_by_file_io and x$...
it materializes that result into a temporary table. Any subsequent time the result is needed, MySQL refers again to the temporary table. The optimizer may index the table with a hash index to make lookups fast and inexpensive. The index contains unique values to eliminate duplicates and make ...
and receive a full description of the definition. * Most importantly this shortcoming becomes problematic when a super user like root tries to perform an export using mysql-dump. This client evidently uses SHOW CREATE VIEW in order to read out the contents of views, and if the view is SQL ...
INDEX (stock_code, order_type, datetime) INDEX (stock_code, datetime) I see you have turned off the slowlog: #log-slow-queries=/var/log/mysqld.slow.log #long_query_time=1 It can be a useful tool in figuring out slow queries. ...