关于表的索引 · k8s原理与实践

[TOC] # 关于表的索引可以在表的一个或多个列上创建索引以加速表上的 SQL 语句执行速度。索引使用正确的话，可以减少物理 IO 或者逻辑 IO。如果创建表时同时设置了主键，OceanBase 数据库会默认创建一个唯一索引。以下面的 SQL 为例： ~~~ obclient> DROP TABLE IF EXISTS t1; Query OK, 0 rows affected (0.01 sec) obclient> CREATE TABLE t1(id bigint not null primary key, name varchar(50)); Query OK, 0 rows affected (0.05 sec) obclient> show indexes from t1\G *************************** 1. row *************************** Table: t1 Non_unique: 0 Key_name: PRIMARY Seq_in_index: 1 Column_name: id Collation: A Cardinality: NULL Sub_part: NULL Packed: NULL Null: Index_type: BTREE Comment: available Index_comment: Visible: YES 1 row in set (0.01 sec) ~~~ ## 新增索引为表增加索引可以通过 CREATE INDEX 语句。OceanBase 能在普通表和分区表上创建索引，索引可以是本地索引或者全局索引。同时索引可以是唯一索引或者普通索引，如果是分区表的唯一索引，唯一索引必须包含表分区的拆分键。创建索引的 SQL 语法格式如下： ~~~ CREATE [UNIQUE] INDEX index_name ON table_name ( column_list ) [LOCAL | GLOBAL] [ PARTITION BY column_list PARTITIONS N ] ; ~~~ MySQL 租户里，索引名称在表范围内不能重复，查看索引可以通过命令 SHOW INDEXES 。在 MySQL 租户里，新增索引还有一种方法，SQL 语法格式如下： ~~~ ALTER TABLE table_name ADD|DROP INDEX|KEY index_name ( column_list ) ; ~~~ 可以一次增加多个索引，索引关键字用 INDEX 或 KEY 都可以。 * 示例：对分区表新增索引 ~~~ obclient> create table t3( id bigint not null primary KEY , name varchar(50) , gmt_create timestamp not null default current_timestamp ) partition by hash(id) partitions 8; Query OK, 0 rows affected (0.14 sec) obclient> alter table t3 add unique key t3_uk (name) local; ERROR 1503 (HY000): A UNIQUE INDEX must include all columns in the table's partitioning function obclient> alter table t3 add unique key t3_uk (name, id) LOCAL , add key t3_ind3(gmt_create) global; Query OK, 0 rows affected (18.03 sec) obclient> show indexes from t3; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+ | t3 | 0 | PRIMARY | 1 | id | A | NULL | NULL | NULL | | BTREE | available | | YES | | t3 | 0 | t3_uk | 1 | name | A | NULL | NULL | NULL | YES | BTREE | available | | YES | | t3 | 0 | t3_uk | 2 | id | A | NULL | NULL | NULL | | BTREE | available | | YES | | t3 | 1 | t3_ind3 | 1 | gmt_create | A | NULL | NULL | NULL | | BTREE | available | | YES | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+ 4 rows in set (0.01 sec) ~~~ ## 删除索引删除索引的语法格式如下： ~~~ ALTER TABLE table_name DROP key|index index_name ; ~~~ * 示例：删除表的索引 ~~~ obclient> alter table t3 drop key t3_uk, drop key t3_ind3; Query OK, 0 rows affected (0.07 sec) ~~~