openGauss每日一练第15天 |逻辑结构：表管理3

openGauss每日一练第15天 |逻辑结构：表管理3

openGauss逻辑结构：表管理3

学习目标

学习查看表的相关信息

课程学习

1.测试环境准备

--首先创建一张测试表。
omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
omm=# create table test(
omm(# id bigint,
omm(# name varchar(50) not null,
omm(# age  int default 20,
omm(# primary key(id)
omm(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=# 

2.在gsql中查看表的定义、模式和所有者

--在gsql中，使用\d tableNmae命令查看表的定义。
omm=# \d+ test;
                                 Table "public.test"
 Column |         Type          | Modifiers  | Storage  | Stats target | Description 
--------+-----------------------+------------+----------+--------------+-------------
 id     | bigint                | not null   | plain    |              | 
 name   | character varying(50) | not null   | extended |              | 
 age    | integer               | default 20 | plain    |              | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
Has OIDs: no
Options: orientation=row, compression=no

omm=# 

--在gsql中，使用\d tableNmae命令查看表的模式和所有者。
omm=# \dt+ test;
                                    List of relations
 Schema | Name | Type  | Owner |  Size   |             Storage              | Description 
--------+------+-------+-------+---------+----------------------------------+-------------
 public | test | table | omm   | 0 bytes | {orientation=row,compression=no} | 
(1 row)

omm=# 

3.查看某个模式下有哪些表

--查看public模式下的所有表名：
omm=# SELECT table_name FROM information_schema.tables WHERE table_schema='public';
 table_name 
------------
 test
(1 row)

omm=#

4.查看一个表下有哪些约束

--查看约束名称、约束类型
omm=# select conname, connamespace, contype, conkey     
omm-#   from pg_constraint 
omm-#  where conrelid in (  select oid
omm(#                   from pg_class
omm(#                  where relname='test');
  conname  | connamespace | contype | conkey 
-----------+--------------+---------+--------
 test_pkey |         2200 | p       | {1}
(1 row)

omm=# 

--或者使用gsql的元命令\d tableName很方便地查看一个表上有哪些约束
omm=#  \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# 

5.查看一个表属于数据库的哪个模式

omm=# \x 
Expanded display is on.
SELECT * FROM information_schema.tables WHERE table_name='test';
-[ RECORD 1 ]----------------+-----------
table_catalog                | omm
table_schema                 | public
table_name                   | test
table_type                   | BASE TABLE
self_referencing_column_name | 
reference_generation         | 
user_defined_type_catalog    | 
user_defined_type_schema     | 
user_defined_type_name       | 
is_insertable_into           | YES
is_typed                     | NO
commit_action                | 

omm=# 

课程作业

1.创建表和约束

omm=# drop table if exists lxs1;
NOTICE:  table "lxs1" does not exist, skipping
DROP TABLE
omm=# create table lxs1(
omm(#  id int default 1,
omm(#  info text not null,
omm(#  primary key(id)
omm(# );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "lxs1_pkey" for table "lxs1"
CREATE TABLE
omm=#

2.使用\d tableNmae命令查看表的定义、模式和所有者

omm=# \d lxs1
          Table "public.lxs1"
 Column |  Type   |     Modifiers      
--------+---------+--------------------
 id     | integer | not null default 1
 info   | text    | not null
Indexes:
    "lxs1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# \d+ lxs1
                              Table "public.lxs1"
 Column |  Type   |     Modifiers      | Storage  | Stats target | Description 
--------+---------+--------------------+----------+--------------+-------------
 id     | integer | not null default 1 | plain    |              | 
 info   | text    | not null           | extended |              | 
Indexes:
    "lxs1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
Has OIDs: no
Options: orientation=row, compression=no

omm=# \dt lxs1
                        List of relations
 Schema | Name | Type  | Owner |             Storage              
--------+------+-------+-------+----------------------------------
 public | lxs1 | table | omm   | {orientation=row,compression=no}
(1 row)

omm=# \dt+ lxs1
                                      List of relations
 Schema | Name | Type  | Owner |    Size    |             Storage              | Description 
--------+------+-------+-------+------------+----------------------------------+-------------
 public | lxs1 | table | omm   | 8192 bytes | {orientation=row,compression=no} | 
(1 row)

omm=#

3.查看某个模式下有哪些表

omm=# SELECT table_name FROM information_schema.tables WHERE table_schema='public';
 table_name 
------------
 test
 lxs1
(2 rows)

omm=# 

4.查看一个表下有哪些约束

omm=# select conname, connamespace, contype, conkey     
omm-#   from pg_constraint 
omm-#  where conrelid in (  select oid
omm(#                   from pg_class
omm(#                  where relname='lxs1');
  conname  | connamespace | contype | conkey 
-----------+--------------+---------+--------
 lxs1_pkey |         2200 | p       | {1}
(1 row)

omm=#

5.查看一个表属于数据库的哪个模式

omm=# \x
Expanded display is on.
omm=# SELECT * FROM information_schema.tables WHERE table_name='lxs1';
-[ RECORD 1 ]----------------+-----------
table_catalog                | omm
table_schema                 | public
table_name                   | lxs1
table_type                   | BASE TABLE
self_referencing_column_name | 
reference_generation         | 
user_defined_type_catalog    | 
user_defined_type_schema     | 
user_defined_type_name       | 
is_insertable_into           | YES
is_typed                     | NO
commit_action                | 

omm=# 

–学如逆水行舟，不进则退。