關于表的索引 · k8s原理與實踐

[TOC] # 關于表的索引可以在表的一個或多個列上創建索引以加速表上的 SQL 語句執行速度。索引使用正確的話，可以減少物理 IO 或者邏輯 IO。如果創建表時同時設置了主鍵，OceanBase 數據庫會默認創建一個唯一索引。以下面的 SQL 為例： ~~~ 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) ~~~ ## 新增索引為表增加索引可以通過 CREATE INDEX 語句。OceanBase 能在普通表和分區表上創建索引，索引可以是本地索引或者全局索引。同時索引可以是唯一索引或者普通索引，如果是分區表的唯一索引，唯一索引必須包含表分區的拆分鍵。創建索引的 SQL 語法格式如下： ~~~ CREATE [UNIQUE] INDEX index_name ON table_name ( column_list ) [LOCAL | GLOBAL] [ PARTITION BY column_list PARTITIONS N ] ; ~~~ MySQL 租戶里，索引名稱在表范圍內不能重復，查看索引可以通過命令 SHOW INDEXES 。在 MySQL 租戶里，新增索引還有一種方法，SQL 語法格式如下： ~~~ ALTER TABLE table_name ADD|DROP INDEX|KEY index_name ( column_list ) ; ~~~ 可以一次增加多個索引，索引關鍵字用 INDEX 或 KEY 都可以。 * 示例：對分區表新增索引 ~~~ 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) ~~~ ## 刪除索引刪除索引的語法格式如下： ~~~ ALTER TABLE table_name DROP key|index index_name ; ~~~ * 示例：刪除表的索引 ~~~ obclient> alter table t3 drop key t3_uk, drop key t3_ind3; Query OK, 0 rows affected (0.07 sec) ~~~