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。
Now to add an index and do explain: mysql> alter table view1 add index(i); mysql> explain -> select * from viewn where i = 2\G *** 1. row *** id: 1 select_type: PRIMARY table: <derived2> type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 4 Extra:...
百度试题 题目MySQL中创建存储过程的关键字是() A.procB.procedureC.viewD.index相关知识点: 试题来源: 解析 B欢迎编辑补充或参与题目讨论 反馈 收藏
This view is most useful when the server has been up and processing long enough that its workload is representative. Otherwise, presence of an index in this view may not be meaningful. The schema_unused_indexes view has these columns: object...
create index ix_name_email on in3(name,email); 1. 创建索引 如上创建组合索引之后,查询: name and email -- 使用索引 name -- 使用索引 email -- 不使用索引 注意:对于同时搜索n个条件时,组合索引的性能好于多个单一索引合并。
This view is most useful when the server has been up and processing long enough that its workload is representative. Otherwise, presence of an index in this view may not be meaningful. The schema_unused_indexes view has these columns: object...
百度试题 题目在MySQL中,建立数据库用的命令是( )A.Create DataBaseB.Create TableC.Create ViewD.Create Index 相关知识点: 试题来源: 解析 A 反馈 收藏
with an index, and it benefits similarly from the generated index. The overhead of index creation is negligible compared to the cost of query execution without the index. If ref access would result in higher cost than some other access method, the optimizer creates no index and loses nothing...
the key index column also return NULL. This circumstance is bad. When query from a view with simply "union all" tables, I expect mysql will base on the where condition to find out all desired records for each table first and then merge them into a big record set and then return. (whi...