openGauss每日一练第17天-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  t1(id serial primary key ,testnum serial);
NOTICE:  CREATE TABLE will create implicit sequence "t1_id_seq" for serial column "t1.id"
NOTICE:  CREATE TABLE will create implicit sequence "t1_testnum_seq" for serial column "t1.testnum"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t1_pkey" for table "t1"
CREATE TABLE
omm=# create index idx_t_testnum on t1(testnum);
omm=# CREATE INDEX

omm=# \di
                    List of relations
 Schema |     Name      | Type  | Owner | Table | Storage 
--------+---------------+-------+-------+-------+---------
 public | idx_t_testnum | index | omm   | t1    | 
 public | t1_pkey       | index | omm   | t1    | 
(2 rows)
```
2.通过hint使用索引
```sql

omm=# --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(# ca_location_type character(20)
omm(# );
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
omm=# 
omm=# --创建索引
omm=# 
omm=# create index customer_idx on  customer(ca_address_sk);
CREATE INDEX
omm=# 
omm=# --通过hint强制使用索引，查看执行计划
omm=# 
omm=# EXPLAIN SELECT /*+ indexscan(customer customer_idx ) */ 
omm-#  * FROM customer WHERE ca_address_sk<100;
                                  QUERY PLAN                                   
-------------------------------------------------------------------------------
 [Bypass]
 Index Scan using customer_idx on customer  (cost=0.00..8.27 rows=1 width=788)
   Index Cond: (ca_address_sk < 100)
(3 rows)

omm=# create index customer_idx on  customer(ca_address_sk);
ERROR:  relation "customer_idx" already exists
omm=# EXPLAIN SELECT /*+ indexscan(customer customer_idx ) */ 
omm-#  * FROM customer WHERE ca_address_sk<100;
                                  QUERY PLAN                                   
-------------------------------------------------------------------------------
 [Bypass]
 Index Scan using customer_idx on customer  (cost=0.00..8.27 rows=1 width=788)
   Index Cond: (ca_address_sk < 100)
(3 rows)

```
3.rename索引

```sql

omm=# ALTER INDEX idx_test_testnum_new RENAME TO idx_t_testnum_1;
ALTER INDEX

```4.重建索引
```sql
--重建一个单独索引
omm=# alter index idx_t_testnum_1 rebuild;
REINDEX
omm=# reindex index idx_t_testnum_1;
REINDEX
--重建所有索引
omm=# reindex table t1;
REINDEX

```
5.移动索引到其他表空间
```sql

omm=# create tablespace t_its relative location 'taglespace/t_index_tbs';
CREATE TABLESPACE
 
omm=# alter index idx_t_testnum_1 set tablespace t_its;
ALTER INDEX

omm=# select * from pg_indexes where tablename='t1';
 schemaname | tablename |    indexname    | tablespace |                                 indexdef                                 
 
------------+-----------+-----------------+------------+--------------------------------------------------------------------------
-
 public     | t1        | t1_pkey         |            | CREATE UNIQUE INDEX t1_pkey ON t1 USING btree (id) TABLESPACE pg_default
 public     | t1        | idx_t_testnum_1 | t_its      | CREATE INDEX idx_t_testnum_1 ON t1 USING btree (testnum) TABLESPACE t_its
(2 rows)
```
6.删除索引
```sql

omm=# drop index idx_t_testnum_1;
DROP INDEX

```
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