0.学习内容与环境进入

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。
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。

/*+ <plan hint>*/
select /*+ <plan_hint1> <plan_hint2> */ * from t1, (select /*+ <plan_hint3> */ from t2) where 1=1;

• Hints
  Currently, the following hints are supported:

  • Join order hints (leading)
  • Join operation hints, excluding the semi join, anti join, and unique plan hints
  • Rows hints
  • Scan operation hints, supporting only tablescan, indexscan, and indexonlyscan
  • Sublink name hints

• Precautions

  • Hints do not support Agg, Sort, Setop, or Subplan.

• 查看表约束

`\d <tablename>`
create index <index-name> on <table>(<column-name>);

• 修改表字段默认值
  alter table t1 set column <name> default <value>;

• 进入环境

su - omm
gsql -r

\l

1. 创建表，在表中创建索引

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');

create index customer_idx on  customer(ca_address_sk);

2.通过hint使用索引

hint的语法用 /*+ indexscan*/

EXPLAIN SELECT /*+ indexscan(customer customer_idx ) */
 * FROM customer WHERE ca_address_sk<100;

ALTER INDEX customer_idx RENAME TO customer_idx_new;
\d customer

4.重建索引

ALTER INDEX  customer_idx_new REBUILD;

REINDEX INDEX customer_idx_new;

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customer_idx_new移动到表空间myindex_ts：

ALTER INDEX customer_idx_new SET TABLESPACE myindex_ts;

• 查看索引所在的表空间

 select tablespace from pg_indexes where tablename = 'customer';

6.删除索引

• 执行下面的命令，删除表test上的索引customer_idx_new：

drop index customer_idx_new;