openGauss 每日一练第17天

学习目标

掌握openGauss DBMS索引的管理：创建索引、删除索引、查询索引的信息、修改索引的信息。

课程学习

索引是一个指向表中数据的指针。一个数据库中的索引与一本书的索引目录是非常相似的。
索引可以用来提高数据库查询性能，但是不恰当的使用将导致数据库性能下降。

1.创建索引

--为表test的testnum列创建一个索引
su - omm
gsql -r

drop table if exists test;
create table test(id serial primary key,testnum serial);

create index idx_test_testnum on test(testnum);

--查看索引
\di

2.通过hint使用索引

--测试准备，创建表customer，并插入数据
CREATE TABLE customer
(
ca_address_sk integer NOT NULL ,
ca_address_id character(16),
ca_street_number character(10) ,
ca_street_name character varying(60) ,
ca_street_type character(15) ,
ca_suite_number character(10) ,
ca_city character varying(60) ,
ca_county character varying(30) ,
ca_state character(2) ,
ca_zip character(10) ,
ca_country character varying(20) ,
ca_gmt_offset numeric(5,2) ,
ca_location_type character(20)
);
insert into customer values
(1, 'AAAAAAAABAAAAAAA', '18', 'Jackson', 'Parkway', 'Suite 280', 'Fairfield', 'Maricopa County', 'AZ', '86192' ,'United States', -7.00, 'condo'),
(2, 'AAAAAAAACAAAAAAA', '362', 'Washington 6th', 'RD', 'Suite 80', 'Fairview', 'Taos County', 'NM', '85709', 'United States', -7.00, 'condo'),
(3, 'AAAAAAAADAAAAAAA', '585', 'Dogwood Washington', 'Circle', 'Suite Q', 'Pleasant Valley', 'York County', 'PA', '12477', 'United States', -5.00, 'single family');

--创建索引

create index customer_idx on  customer(ca_address_sk);

--通过hint强制使用索引，查看执行计划

EXPLAIN SELECT /*+ indexscan(customer customer_idx ) */ 
 * FROM customer WHERE ca_address_sk<100;

3.rename索引

ALTER INDEX idx_test_testnum RENAME TO idx_test_testnum_new;

4.重建索引

--重建一个单独索引
ALTER INDEX  idx_test_testnum_new REBUILD;

REINDEX INDEX  idx_test_testnum_new;
--重建所有索引
reindex table test;

5.移动索引到其他表空间

--创建表空间myindex_ts：
 CREATE TABLESPACE myindex_ts RELATIVE LOCATION 'tablespace/myindex_ts1';

--将索引idx_test_testnum_new移动到表空间myindex_ts：
  ALTER INDEX idx_test_testnum_new SET TABLESPACE myindex_ts;

--查看索引所在的表空间
 select * from pg_indexes where tablename = 'test';
--或
 select * from pg_indexes where indexname = 'idx_test_testnum_new';

1. 删除索引

--执行下面的命令，删除表test上的索引idx_test_testnum_new：

drop index idx_test_testnum_new;

课程作业

准备

su - omm
gsql -r
-- 创建tablespace test01_tbs;

omm=# create tablespace test01_tbs relative location 'tablespaces/test01_tbs';
CREATE TABLESPACE
omm=# create tablespace test02_tbs relative location 'tablespaces/test02_tbs';
CREATE TABLESPACE

1.创建表，在表中创建索引

omm=# create table test01(id serial primary key, num serial, remark varchar(200));
NOTICE:  CREATE TABLE will create implicit sequence "test01_id_seq" for serial column "test01.id"
NOTICE:  CREATE TABLE will create implicit sequence "test01_num_seq" for serial column "test01.num"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test01_pkey" for table "test01"
CREATE TABLE

-- 为num 创建索引名称为 idx_mum , 表空间位于 test01_tbs

omm=# create index idx_num on test01(num) tablespace test01_tbs;
CREATE INDEX

-- 查看当前表中的索引
omm=# \di
                    List of relations
 Schema |    Name     | Type  | Owner | Table  | Storage 
--------+-------------+-------+-------+--------+---------
 public | idx_num     | index | omm   | test01 | 
 public | test01_pkey | index | omm   | test01 | 
(2 rows)

-- 插入一些数据
omm=# insert into test01 (remark) values ('ssssss');
INSERT 0 1
omm=# insert into test01 (remark) values ('ssssss');
INSERT 0 1
omm=# insert into test01 (remark) values ('ssssss');
INSERT 0 1
omm=# insert into test01 (remark) values ('ssssss');
INSERT 0 1
omm=# insert into test01 (remark) values ('sssss11s');
INSERT 0 1
omm=# insert into test01 (remark) values ('sssss1s');21s');
INSERT 0 1
-- 查询表中的数据
omm=# select * from test01;
 id | num |  remark  
----+-----+----------
  3 |   3 | 
  4 |   3 | 
  5 |   3 | 
  6 |   3 | 
  7 |   3 | 
  8 |   3 | 
  9 |   3 | 
 10 |   4 | test
 11 |   5 | ssssss
 12 |   6 | ssssss
 13 |   7 | ssssss
 14 |   8 | ssssss
 15 |   9 | sssss11s
 16 |  10 | sssss21s
(14 rows)

2.通过hint使用索引

-- 不通过 hint ，可以看出默认走了idx_num 的索引
omm=# explain select * from test01 where num=7;
                               QUERY PLAN                               
------------------------------------------------------------------------
 [Bypass]
 Index Scan using idx_num on test01  (cost=0.00..8.27 rows=1 width=426)
   Index Cond: (num = 7)
(3 rows)

-- 通过hint 走索引 idx_num
omm=# explain select /*+ indexscan(test01 idx_num) */ * from test01 where num = 7;
                               QUERY PLAN                               
------------------------------------------------------------------------
 [Bypass]
 Index Scan using idx_num on test01  (cost=0.00..8.27 rows=1 width=426)
   Index Cond: (num = 7)
(3 rows)

3.rename索引

-- 将idx_num 重命名为 idx_num01
omm=# alter index idx_num rename to idx_num01;
ALTER INDEX

-- 查询索引，可以看到名称已经更改为 idx_num01;
omm=# \di
                    List of relations
 Schema |    Name     | Type  | Owner | Table  | Storage 
--------+-------------+-------+-------+--------+---------
 public | idx_num01   | index | omm   | test01 | 
 public | test01_pkey | index | omm   | test01 | 
(2 rows)

4.重建索引

-- 重建指定的索引 idx_num01
omm=# alter index idx_num01 rebuild;
REINDEX

-- 重建test01 库中所有的索引
omm=# reindex table test01;
REINDEX

5.移动索引到其他表空间

-- 查询当前idx_num01 的表空间，可以看到当前表空间为 test01_tbs
omm=# select  * from pg_indexes where indexname = 'idx_num01';
 schemaname | tablename | indexname | tablespace |                                 indexdef                                 
------------+-----------+-----------+------------+--------------------------------------------------------------------------
 public     | test01    | idx_num01 | test01_tbs | CREATE INDEX idx_num01 ON test01 USING btree (num) TABLESPACE test01_tbs
(1 row)

-- 将idx_num01 的表空间挪动到 test02_tbs
omm=# alter index idx_num01 set tablespace test02_tbs ;
ALTER INDEX

-- 再次查看索引详情，发现 idx_num01的 表空间已经变更为 test02_tbs
omm=# select * from pg_indexes where indexname ='idx_num01';
 schemaname | tablename | indexname | tablespace |                                 indexdef                                 
------------+-----------+-----------+------------+--------------------------------------------------------------------------
 public     | test01    | idx_num01 | test02_tbs | CREATE INDEX idx_num01 ON test01 USING btree (num) TABLESPACE test02_tbs
(1 row)

6.删除索引

-- 删除索引 idx_num01
drop index idx_num01;

-- 查看当前表的索引，发现只剩pk
                    List of relations
 Schema |    Name     | Type  | Owner | Table  | Storage 
--------+-------------+-------+-------+--------+---------
 public | test01_pkey | index | omm   | test01 | 
(1 row)

-- 此时再次执行 explain 查看sql执行计划，发现变为全表扫
omm=# explain select * from test01 where num=7;

                     QUERY PLAN                       
--------------------------------------------------------
 Seq Scan on test01  (cost=0.00..1.18 rows=1 width=426)
   Filter: (num = 7)
(2 rows)