openGauss每日一练第17天-逻辑结构--表管理5

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';
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
```sql
omm=# create table d(id int,name char(30) not null ,age int default 20 ,primary key(id));
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "d_pkey" for table "d"
CREATE TABLE
omm=# create index idx_d_age on d(age);
CREATE INDEX
omm=# \di
                  List of relations
 Schema |   Name    | Type  | Owner | Table | Storage 
--------+-----------+-------+-------+-------+---------
 public | d_pkey    | index | omm   | d     | 
 public | idx_d_age | index | omm   | d     | 
(2 rows)
```
2.通过hint使用索引
```sql

omm=# explain select * from d where age >29omm-# 
;
                      QUERY PLAN                      
------------------------------------------------------
 Seq Scan on d  (cost=0.00..16.30 rows=168 width=132)
omm=#    Filter: (age > 29)
(2 rows)

omm=# explain select /*+indexscan(d idx_d_age) */ * from d where age >29;
                               QUERY PLAN                               
------------------------------------------------------------------------
 [Bypass]
 Index Scan using idx_d_age on d  (cost=0.00..47.19 rows=168 width=132)
   Index Cond: (age > 29)
(3 rows)


```
3.rename索引
```sql
omm=# alter index idx_d_age rename to idx_dage;
ALTER INDEX
omm=# \di
                  List of relations
 Schema |   Name   | Type  | Owner | Table | Storage 
--------+----------+-------+-------+-------+---------
 public | d_pkey   | index | omm   | d     | 
 public | idx_dage | index | omm   | d     | 
(2 rows)



```
4.重建索引

```sql
                             ^
omm=# alter index idx_dage rebuild;
REINDEX
omm=# reindex index idx_dage ;
REINDEX
omm=# reindex table d;
REINDEX


```
5.移动索引到其他表空间
```sql
omm=# create tablespace d_tbs relative location 'tablespace/d_tbs';
CREATE TABLESPACE
omm=# alter index idx_dage set tablespace d_tbs;
ALTER INDEX
omm=# select * from pg_indexes where tablename ='d';
 schemaname | tablename | indexname | tablespace |                                indexdef                                
------------+-----------+-----------+------------+------------------------------------------------------------------------
 public     | d         | d_pkey    |            | CREATE UNIQUE INDEX d_pkey ON d USING btree (id) TABLESPACE pg_default
 public     | d         | idx_dage  | d_tbs      | CREATE INDEX idx_dage ON d USING btree (age) TABLESPACE d_tbs
(2 rows)



```
6.删除索引
```sql

omm=# drop index idx_dage;
DROP INDEX

```