MySQL Index Types MySQL supports several index types, each with its own storage and retrieval characteristics. This tutorial will cover the most commonly used types: BTREE, HASH, FULLTEXT, and SPATIAL indexes.
INDEX关键字用于添加普通索引,后面紧跟索引的名称和列名。 2. 修改表时添加索引 在已有的表中,也可以通过ALTER TABLE语句来添加索引。示例代码如下: ALTERTABLEusersADDINDEXidx_name(name);ALTERTABLEusersADDINDEXidx_email(email); 1. 2. 上述代码在users表上分别添加了name列和email列的索引。ALTER TABLE语句用于...
Extra: Using index condition 4. index_subquery index_subquery替换了以下形式的子查询中的eq_ref访问类型,其中key_column是非唯一索引。 value IN (SELECT key_column FROM single_table WHERE some_expr) index_subquery只是一个索引查找函数,它可以完全替换子查询,提高查询效率。 大多数情况下,使用SELECT子查询时...
(详情见官方文档:https://dev.mysql.com/doc/refman/5.7/en/innodb-index-types.html) 聚集索引这种实现方式使得按主键搜索十分高效,直接能查出整行数据。 在InnoDB中,用非单调递增的字段作为主键不是个好主意,因为InnoDB数据文件本身是一棵B+Tree,非单增的主键会造成在插入新记录时数据文件为了维持B+Tree的特性...
Types of queries that can use a B-Tree index. B-Tree indexes work well for lookups by the full key value, a key range, or a key prefix. They are useful only if the lookup uses a leftmost prefix of the index. Match the full value(全值匹配):A match on the full key value specifie...
https://dev.mysql.com/doc/refman/5.7/en/innodb-index-types.html clustered index(聚簇索引) : https://dev.mysql.com/doc/refman/5.7/en/glossary.html#glos_clustered_index secondary index(二级索引):https://dev.mysql.com/doc/refman/5.7/en/glossary.html#glos_secondary_index ...
4、ENUM枚举类型,每一个值都有对应的索引index。最大两个字节存储,65535个不同成员。注意的是: 表中字段:numbers ('0', '1', '2') insert into test(numbers) values (2),('2'),('3'); select * from test; 会返回: numbers 1 2
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Appendix C Indexes Table of Contents General Index C Function Index Command Index Function Index INFORMATION_SCHEMA Index Join Types Index Operator Index Option Index Privileges Index SQL Modes Index Statement/Syntax Index Status Variable Index System Variable Index Transaction Isolation Level Index...
Gender, Status, Boolean Types etc Unionizing Filesort KEY(A,B) SELECT * FROM TBL WHERE A IN (1,2) ORDER BY B LIMIT 5; Will not be able to use index for SORTING (SELECT * FROM TBL WHERE A=1 ORDER BY B LIMIT 5) UNION ALL (SELECT * FROM TBL WHERE A=2 ORDER BY B LIMIT 5)...