openGauss每日一练第17天 | openGauss逻辑结构：索引管理

原创落笔花生 2022-12-10

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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
root@modb:~# su - omm
omm@modb:~$ gsql -r
gsql ((openGauss 3.0.0 build 02c14696) compiled at 2022-04-01 18:12:00 commit 0 last mr  )
Non-SSL connection (SSL connection is recommended when requiring high-security)
Type "help" for help.

omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
omm=# create table test(id serial primary key,testnum serial);
NOTICE:  CREATE TABLE will create implicit sequence "test_id_seq" for serial column "test.id"
NOTICE:  CREATE TABLE will create implicit sequence "test_testnum_seq" for serial column "test.testnum"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=# create index idx_test_testnum on test(testnum);
CREATE INDEX--查看索引
omm=# \di
                      List of relations
 Schema |       Name       | Type  | Owner | Table | Storage 
--------+------------------+-------+-------+-------+---------
 public | idx_test_testnum | index | omm   | test  | 
 public | test_pkey        | index | omm   | test  | 
(2 rows)

2.通过hint使用索引

--测试准备，创建表customer，并插入数据
omm=# create table customer
omm-# (
omm(# ca_address_sk integer NOT NULL ,
omm(# ca_address_id character(16),
omm(# ca_street_number character(10) ,
omm(# ca_street_name character varying(60) ,
omm(# ca_street_type character(15) ,
omm(# ca_suite_number character(10) ,
omm(# ca_city character varying(60) ,
omm(# ca_county character varying(30) ,
omm(# ca_state character(2) ,
omm(# ca_zip character(10) ,
omm(# ca_country character varying(20) ,
omm(# ca_gmt_offset numeric(5,2) ,
omm(# omm(# ca_location_type character(20)
);
CREATE TABLE
omm=# insert into customer values
omm-#  (1, 'AAAAAAAABAAAAAAA', '18', 'Jackson', 'Parkway', 'Suite 280', 'Fairfield', 'Maricopa County', 'AZ', '86192' ,'United States', -7.00, 'condo'),
omm-#  (2, 'AAAAAAAACAAAAAAA', '362', 'Washington 6th', 'RD', 'Suite 80', 'Fairview', 'Taos County', 'NM', '85709', 'United States', -7.00, 'condo'),
omm-#  (3, 'AAAAAAAADAAAAAAA', '585', 'Dogwood Washington', 'Circle', 'Suite Q', 'Pleasant Valley', 'York County', 'PA', '12477', 'United States', -5.00, 'single family');
INSERT 0 3
--创建索引
omm=# create index customer_idx on  customer(ca_address_sk);
CREATE INDEX
--通过hint强制使用索引，查看执行计划
omm=# explain select /*+ indexcan(customer customer_idx ) */
* from customer where ca_address_sk <100;
WARNING:  LINE 1: syntax error at 'indexcan'
                        QUERY PLAN                        
----------------------------------------------------------
 Seq Scan on customer  (cost=0.00..1.04 rows=1 width=788)
   Filter: (ca_address_sk < 100)
(2 rows)

3.rename索引

omm=# alter index idx_test_testnum rename to idx_test_testnum_new;
ALTER INDEX

4.重建索引

--重建一个单独索引
omm=# alter index idx_test_testnum_new rebuild;
REINDEX
omm=# reindex index idx_test_testnum_new --重建所有索引
omm=# reindex table test ;
REINDEX

5.移动索引到其他表空间

--创建表空间myindex_ts：
omm=# create tablespace myindex_ts relative location 'tablespace/myindex_ts1';
CREATE TABLESPACE
--将索引idx_test_testnum_new移动到表空间myindex_ts：
omm=# alter index idx_test_testnum_new set tablespace myindex_ts ;
ALTER INDEX
--查看索引所在的表空间
omm=# select * from pg_indexes where tablename = 'test';
 schemaname | tablename |      indexname       | tablespace |                                       indexdef                                        
------------+-----------+----------------------+------------+---------------------------------------------------------------------------------------
 public     | test      | test_pkey            |            | CREATE UNIQUE INDEX test_pkey ON test USING btree (id) TABLESPACE pg_default
 public     | test      | idx_test_testnum_new | myindex_ts | CREATE INDEX idx_test_testnum_new ON test USING btree (testnum) TABLESPACE myindex_ts
(2 rows)
--或omm=# select * from pg_indexes where indexname = 'idx_test_testnum_new';
 schemaname | tablename |      indexname       | tablespace |                                       indexdef                                        
------------+-----------+----------------------+------------+---------------------------------------------------------------------------------------
 public     | test      | idx_test_testnum_new | myindex_ts | CREATE INDEX idx_test_testnum_new ON test USING btree (testnum) TABLESPACE myindex_ts
(1 row)

6.删除索引

--执行下面的命令，删除表test上的索引idx_test_testnum_new：
omm=# drop index idx_test_testnum_new;
DROP INDEX

课程作业

1.创建表，在表中创建索引

omm=# create table xx1(id serial primary key,xx1num serial);
NOTICE:  CREATE TABLE will create implicit sequence "xx1_id_seq" for serial column "xx1.id"
NOTICE:  CREATE TABLE will create implicit sequence "xx1_xx1num_seq" for serial column "xx1.xx1num"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "xx1_pkey" for table "xx1"
CREATE TABLE
omm=# create index idx_xx1_xx1num on xx1(xx1num);
CREATE INDEX
omm=# \di
                      List of relations
 Schema |      Name      | Type  | Owner |  Table   | Storage 
--------+----------------+-------+-------+----------+---------
 public | customer_idx   | index | omm   | customer | 
 public | idx_xx1_xx1num | index | omm   | xx1      | 
 public | test_pkey      | index | omm   | test     | 
 public | xx1_pkey       | index | omm   | xx1      | 
(4 rows)