openGauss每日一练打卡第十七天

第17天 | openGauss逻辑结构：索引管理
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’;

6.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
1.创建表，在表中创建索引
create table test1210(id serial primary key,testnum serial);
create index idx_test_testnum1210 on test1210(testnum);

2.通过hint使用索引
CREATE TABLE customer10
(
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 customer10 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’);

create index customer_idx1210 on customer10(ca_address_sk);

–通过hint强制使用索引，查看执行计划

EXPLAIN SELECT /*+ indexscan(customer10 customer_idx1210 ) */

• FROM customer10 WHERE ca_address_sk<100;

3.rename索引

ALTER INDEX idx_test_testnum1210 RENAME TO idx_test_testnum_new1210;

4.重建索引
ALTER INDEX idx_test_testnum_new1210 REBUILD;
REINDEX INDEX idx_test_testnum_new1210;

reindex table test1210;

5.移动索引到其他表空间
CREATE TABLESPACE myindex_ts1210 RELATIVE LOCATION ‘tablespace/myindex_ts1210’;

–将索引idx_test_testnum_new移动到表空间myindex_ts：
ALTER INDEX idx_test_testnum_new1210 SET TABLESPACE myindex_ts1210;

–查看索引所在的表空间
select * from pg_indexes where tablename = ‘test1210’;
–或
select * from pg_indexes where indexname = ‘idx_test_testnum_new1210’;

6.删除索引

drop index idx_test_testnum_new1210;