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

#建表
enmdb=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
enmdb=# create table test(
enmdb(# id serial primary key,
enmdb(# num serial,
enmdb(# name varchar(10)
enmdb(# );
NOTICE:  CREATE TABLE will create implicit sequence "test_id_seq" for serial column "test.id"
NOTICE:  CREATE TABLE will create implicit sequence "test_num_seq" for serial column "test.num"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE

enmdb=# insert into test(name) values('aaa');
INSERT 0 1
enmdb=# insert into test(name) values('bbb');
INSERT 0 1
enmdb=# insert into test(name) values('ccc');
INSERT 0 1

enmdb=# select * from test;
 id | num | name 
----+-----+------
  1 |   1 | aaa
  2 |   2 | bbb
  3 |   3 | ccc
(3 rows)

#创建索引
enmdb=# create index idx_test_num on test(num);
CREATE INDEX
enmdb=#

#查看索引
enmdb=# \di
enmdb=#                     List of relations
 Schema |     Name     | Type  | Owner | Table | Storage 
--------+--------------+-------+-------+-------+---------
 public | idx_test_num | index | omm   | test  | 
 public | test_pkey    | index | omm   | test  | 
(2 rows)

2. 通过hint使用索引

enmdb=# explain select * from test where num < 100 and id < 100;
(5 rows)

                                 QUERY PLAN                                  
-----------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=6.96..22.33 rows=119 width=46)
   Recheck Cond: (num < 100)
   Filter: (id < 100)
   ->  Bitmap Index Scan on idx_test_num  (cost=0.00..6.94 rows=358 width=0)
         Index Cond: (num < 100)

#加hint， 跟oracle的hint非常相似
enmdb=# explain select /*+ indexscan(test test_pkey) */ * from test where num < 100 and id < 100;
                                QUERY PLAN                                
--------------------------------------------------------------------------
 Index Scan using test_pkey on test  (cost=0.00..51.41 rows=119 width=46)
   Index Cond: (id < 100)
   Filter: (num < 100)
(3 rows)

3. rename索引

enmdb=# alter index idx_test_num rename to idx_test_num_new;
ALTER INDEX

#查看索引
enmdb=# \di
                      List of relations
 Schema |       Name       | Type  | Owner | Table | Storage 
--------+------------------+-------+-------+-------+---------
 public | idx_test_num_new | index | omm   | test  | 
 public | test_pkey        | index | omm   | test  | 
(2 rows)

4. 重建索引

#重建指定索引，给出索引名，命令1
enmdb=# alter index idx_test_num_new rebuild;
REINDEX

#重建指定索引，给出索引名，命令2
enmdb=# reindex index idx_test_num_new;
REINDEX

#重建表上所有的索引，给出表名
enmdb=# reindex table test;
REINDEX
enmdb=# \di
                      List of relations
 Schema |       Name       | Type  | Owner | Table | Storage 
--------+------------------+-------+-------+-------+---------
 public | idx_test_num_new | index | omm   | test  | 
 public | test_pkey        | index | omm   | test  | 
(2 rows)

5. 移动索引到其他表空间

enmdb=# create tablespace index_tbs relative location 'tablespace/indx_tbs1';
CREATE TABLESPACE
enmdb=# alter index idx_test_num_new set tablespace index_tbs;
ALTER INDEX

#查看索引所在的表空间, tablespace 空表示使用默认表空间，即跟表所占表空间一致，从indexdef列中的语句可以看出
enmdb=# 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 enmtbs
 public     | test      | idx_test_num_new | index_tbs  | CREATE INDEX idx_test_num_new ON test USING btree (num) TABLESPACE index_tbs
(2 rows)

6. 删除索引

enmdb=# drop index idx_test_num_new;
DROP INDEX