学习目标

创建索引、删除索引、查询索引的信息、修改索引的信息。

作业

1.建表建索引

su - omm
omm-# gsql -r
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=# 
omm=# create index idx_test_testnum on test(testnum);
CREATE INDEX
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

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(# omm(# ca_state character(2) ,
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=# create index customer_idx on  customer(ca_address_sk);
CREATE INDEX
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)

## 3.rename索引
```sql
omm=# ALTER INDEX idx_test_testnum RENAME TO idx_test_testnum_new;
ALTER INDEX
omm=# \di
                         List of relations
 Schema |         Name         | Type  | Owner |  Table   | Storage 
--------+----------------------+-------+-------+----------+---------
 public | customer_idx         | index | omm   | customer | 
 public | idx_test_testnum_new | index | omm   | test     | 
 public | test_pkey            | index | omm   | test     | 
(3 rows)

4.重建索引

omm=# --重建一个单独索引
omm=# ALTER INDEX  idx_test_testnum_new REBUILD;

omm=# REINDEX
omm=# REINDEX INDEX  idx_test_testnum_new;
REINDEX
omm=# --重建所有索引
omm=# reindex table test;
REINDEX
omm=# 

5.移动索引到其他表空间

omm=# --创建表空间myindex_ts：
omm=#  CREATE TABLESPACE myindex_ts RELATIVE LOCATION 'tablespace/myindex_ts1';
CREATE TABLESPACE
omm=# 
omm=# --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
omm=# 
omm=# --查看索引所在的表空间
omm=#  select * from pg_indexes where tablename = 'test';
) 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)

 schemaname | tablename |      indexname       | tablespace |                                       indexdef       
                                 
------------+-----------+----------------------+------------+------------------------------------------------------
---------------------------------
 public     | test      | test_pkey            |            | CREATE UNIQUE INDEX test_pkey ON test USING btree (id
omm=# --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

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

总结

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。