Greenplum表的管理實踐-1

本文章主要介紹和實踐如何創建、修改、刪除表，包括臨時表的管理，同時針對表的約束，包括非空，唯一，主外鍵，默認等，另外還會簡單進行數據的插入和修改，刪除的實驗操作。

首先需要申明的是Greenplum數據庫的表與任何一種關係型數據庫中的表類似，不過其表中的行被分佈在系統中的不同Segment上。當用戶創建一個表時，用戶會指定該表的分佈策略。

Greenplum的表分佈策略，存儲特殊屬性，已經大表的分區，我會在表實踐-2上進行總結整理。

Greenplum創建的表的策略或者注意事項：

該表的列以及它們的數據類型。參見選擇列的數據類型。
任何用於限制列或者表中能包含的數據的表或者列約束。參見設置表和列約束。
表的分佈策略，這決定了Greenplum數據庫如何在Segment之間劃分數據。參見選擇表分佈策略。
表存儲在磁盤上的方式。參見選擇表存儲模型。
大型表的表分區策略。參見創建和管理數據庫。

1 創建表

create table department(deptid int not null,
                       deptname varchar(20),
                       createtime timestamp)
                       DISTRIBUTED BY(deptid);
                       

archdata=# create table department(deptid int not null,
archdata(#                        deptname varchar(20),
archdata(#                        createtime timestamp)
archdata-#                        DISTRIBUTED BY(deptid);
CREATE TABLE
archdata=# 
archdata=# 
archdata=# \dt department
                List of relations
 Schema |    Name    | Type  |  Owner  | Storage 
--------+------------+-------+---------+---------
 public | department | table | gpadmin | heap
(1 row)

archdata=# \dt+ department
                       List of relations
 Schema |    Name    | Type  |  Owner  | Storage | Description 
--------+------------+-------+---------+---------+-------------
 public | department | table | gpadmin | heap    | 
(1 row)  

 查看錶大小
         
 select pg_size_pretty(pg_relation_size('department'));
         
archdata=#  select pg_size_pretty(pg_relation_size('department'));
 pg_size_pretty 
----------------
 0 bytes
(1 row)

archdata=#

2 創建臨時表

PostgreSQL支持兩類臨時表，會話級和事務級臨時表。在會話級別的臨時表中，在整個會話的生命週期中，數據一直保存。事務級臨時表，數據只存在於這個事務的生命週期中。不指定臨時表的屬性，

PostgreSQL中，不管是事務級還是會話級臨時表，當會話結束時，臨時表就會消失。這與oracle數據庫不同，在oracle數據庫中，只是臨時表中的數據消失，而臨時表還存在。

PostgreSQL臨時表是schema下所生成的一個特殊的表，這個schema的名稱爲“pg_temp_n”，其中n代表數字，不同的session數字不同。

一個會話創建的臨時表不能被其他會話訪問。

默認情況下，創建的臨時表是會話級的，如果需要創建事務。需要添加“on commit delete rows”子句。（注：“on commit”子句形式有三種：“on commit preserve rows”，默認值，會話級；“on commit delete rows”，事務級，事務結束，刪除數據；“on commit drop”，事務級，事務結束，刪除臨時表）

創建臨時表的關鍵字“temporary”可以縮寫爲“temp”。

PostgreSQL爲了與其他數據庫創建臨時表的語句保持兼容，還沒有“GLOBAL”和“LOCAL”關鍵字，但兩個關鍵字沒有用處。

2.1 會話級臨時表

創建臨時表

create temporary table temp_t as select * from pg_class;

archdata=# create temporary table temp_t as select * from pg_class;
NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column(s) named 'relname' as the Greenplum Database data distribution key for this table.
HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
SELECT 411

archdata=# \dt pg_class;
                 List of relations
   Schema   |   Name   | Type  |  Owner  | Storage 
------------+----------+-------+---------+---------
 pg_catalog | pg_class | table | gpadmin | heap
(1 row)

archdata=# select count(*) from pg_class;
 count 
-------
   411
(1 row)

archdata=# 

在本session中是可以看到表的
archdata-# \dt temp_t
                 List of relations
    Schema    |  Name  | Type  |  Owner  | Storage 
--------------+--------+-------+---------+---------
 pg_temp_1428 | temp_t | table | gpadmin | heap
(1 row)

archdata-#

在其他session中去查詢相關臨時表

archdata=# select pg_backend_pid();
 pg_backend_pid 
----------------
           4334
(1 row)

\dt temp_t
archdata=# \dt temp_t
No matching relations found.
archdata=# 

發現直接/dt的方式是查詢不到temp表的

指定schema方式進行
\dt pg_temp_1428.temp_t
archdata-# \dt pg_temp_1428.temp_t
                 List of relations
    Schema    |  Name  | Type  |  Owner  | Storage 
--------------+--------+-------+---------+---------
 pg_temp_1428 | temp_t | table | gpadmin | heap
(1 row)

archdata-# 
archdata=# select * from  pg_temp_1428.temp_t;
                            relname                             | relnamespace | reltype | relowner |
 relam | relfilenode | reltablespace | relpages | reltuples | reltoastrelid | reltoastidxid | relhasi
ndex | relisshared | relkind | relstorage | relnatts | relchecks | reltriggers | relukeys | relfkeys 
| relrefs | relhasoids | relhaspkey | relhasrules | relhassubclass | relfrozenxid |                re
lacl                 | reloptions 
----------------------------------------------------------------+--------------+---------+----------+
-------+-------------+---------------+----------+-----------+---------------+---------------+--------
-----+-------------+---------+------------+----------+-----------+-------------+----------+----------
+---------+------------+------------+-------------+--------------

2.2 創建會話級別的臨時表

archdata=# create temporary table temp_t2(id int,note text) on commit delete rows;
NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'id' as the Greenplum Database data distribution key for this table.
HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
CREATE TABLE
archdata=#

archdata=# insert into temp_t2 values(1,'a');
INSERT 0 1
archdata=# 
archdata=# select * from temp_t2;
 id | note 
----+------
(0 rows) ---看不到記錄了

archdata=# 

使用事務控制方式

postgres=# begin;
BEGIN
postgres=# insert into temp_t2 values(1,'a');
INSERT 0 1
postgres=# insert into temp_t2 values(1,'b');
INSERT 0 1
postgres=# select * from temp_t2;
 id | note
----+------
  1 | a
  1 | b
(2 行記錄)
postgres=# end;
COMMIT
postgres=# select * from temp_t2;
 id | note
----+------
(0 行記錄)


看到在事務結束後，表中的數據也都沒有了，在別的會話中也是無法看到這個臨時表的。

3 約束

3.1 字段級別的check

archdata=# CREATE TABLE department1 (
archdata(# deptid int NOT NULL,
archdata(# deptname varchar(20),
archdata(# createtime timestamp CONSTRAINT create_check CHECK (createtime > '1970-01-01')
archdata(# ) DISTRIBUTED BY(deptid);
CREATE TABLE
archdata=# 
archdata=# 
archdata=# \dt department1
                List of relations
 Schema |    Name     | Type  |  Owner  | Storage 
--------+-------------+-------+---------+---------
 public | department1 | table | gpadmin | heap
(1 row)

archdata=# \d department1
              Table "public.department1"
   Column   |            Type             | Modifiers 
------------+-----------------------------+-----------
 deptid     | integer                     | not null
 deptname   | character varying(20)       | 
 createtime | timestamp without time zone | 
Check constraints:
    "create_check" CHECK (createtime > '1970-01-01 00:00:00'::timestamp without time zone)
Distributed by: (deptid)

archdata=#

3.2 表級的check

archdata=# CREATE TABLE department2 (
archdata(# deptid int NOT NULL,
archdata(# deptname varchar(20) not null,
archdata(# createtime timestamp,
archdata(# parentcreatetime timestamp,
archdata(# check(parentcreatetime>createtime)
archdata(# ) DISTRIBUTED BY(deptid);
CREATE TABLE
archdata=# 
archdata=# 
archdata=# \d department2
                 Table "public.department2"
      Column      |            Type             | Modifiers 
------------------+-----------------------------+-----------
 deptid           | integer                     | not null
 deptname         | character varying(20)       | not null
 createtime       | timestamp without time zone | 
 parentcreatetime | timestamp without time zone | 
Check constraints:
    "department2_check" CHECK (parentcreatetime > createtime)
Distributed by: (deptid)

archdata=#

3.3 非空約束

關鍵字NOT NULL

archdata=# CREATE TABLE department3 (
archdata(# deptid int NOT NULL check (deptid>0),
archdata(# deptname varchar(20) not null,
archdata(# createtime timestamp,
archdata(# parentcreatetime timestamp
archdata(# ) DISTRIBUTED BY(deptid);
CREATE TABLE
archdata=# \d department3
                 Table "public.department3"
      Column      |            Type             | Modifiers 
------------------+-----------------------------+-----------
 deptid           | integer                     | not null
 deptname         | character varying(20)       | not null
 createtime       | timestamp without time zone | 
 parentcreatetime | timestamp without time zone | 
Check constraints:
    "department3_deptid_check" CHECK (deptid > 0)
Distributed by: (deptid)

archdata=#

3.4 唯一約束

關鍵件unique

archdata=# CREATE TABLE department4  (
archdata(# deptid int unique,
archdata(# deptname varchar(20) not null,
archdata(# createtime timestamp,
archdata(# parentcreatetime timestamp
archdata(# ) DISTRIBUTED BY(deptid);
NOTICE:  CREATE TABLE / UNIQUE will create implicit index "department4_deptid_key" for table "department4"
CREATE TABLE
archdata=# \d department4
                 Table "public.department4"
      Column      |            Type             | Modifiers 
------------------+-----------------------------+-----------
 deptid           | integer                     | 
 deptname         | character varying(20)       | not null
 createtime       | timestamp without time zone | 
 parentcreatetime | timestamp without time zone | 
Indexes:
    "department4_deptid_key" UNIQUE, btree (deptid)
Distributed by: (deptid)

archdata=# \di department4
No matching relations found.
archdata=# \di department4_deptid_key
                             List of relations
 Schema |          Name          | Type  |  Owner  | Storage |    Table    
--------+------------------------+-------+---------+---------+-------------
 public | department4_deptid_key | index | gpadmin | heap    | department4
(1 row)

archdata=#

3.5 主鍵約束

關鍵是primary key，就是唯一非空的，主鍵可以多個字段組合。

CREATE TABLE department5  (
	deptid int pr1mary key,
	deptname varchar(20) not null,
	createtime timestamp,
	parentcreatetime timestamp
) DISTRIBUTED BY(deptid);


archdata=# CREATE TABLE department5  (
archdata(# deptid int primary key,
archdata(# deptname varchar(20) not null,
archdata(# createtime timestamp,
archdata(# parentcreatetime timestamp
archdata(# ) DISTRIBUTED BY(deptid);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "department5_pkey" for table "department5"
CREATE TABLE
archdata=# 
archdata=# \d department5
                 Table "public.department5"
      Column      |            Type             | Modifiers 
------------------+-----------------------------+-----------
 deptid           | integer                     | not null
 deptname         | character varying(20)       | not null
 createtime       | timestamp without time zone | 
 parentcreatetime | timestamp without time zone | 
Indexes:
    "department5_pkey" PRIMARY KEY, btree (deptid)
Distributed by: (deptid)

archdata=#

3.6 外鍵約束

不支持外鍵,但是語法上允許外鍵約束,但不會起作用。

archdata=# create table emp(
archdata(# empid int not null,
archdata(# empname varchar(20),
archdata(# deptid int not null references department5(deptid),
archdata(# constraint pk_emp primary key(empid))
archdata-# DISTRIBUTED BY(empid);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "emp_pkey" for table "emp"
WARNING:  Referential integrity (FOREIGN KEY) constraints are not supported in Greenplum Database, will not be enforced.
CREATE TABLE
archdata=# 

Greenplum支持外鍵

3.7 默認約束

archdata=# CREATE TABLE department6  (
archdata(# deptid int primary key,
archdata(# deptname varchar(20) not null,
archdata(# createtime timestamp,
archdata(# parentcreatetime timestamp default '2019-01-01 00:00:00'
archdata(# ) DISTRIBUTED BY(deptid);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "department6_pkey" for table "department6"
CREATE TABLE
archdata=# \d department6
                                         Table "public.department6"
      Column      |            Type             |                         Modifiers                  
        
------------------+-----------------------------+----------------------------------------------------
--------
 deptid           | integer                     | not null
 deptname         | character varying(20)       | not null
 createtime       | timestamp without time zone | 
 parentcreatetime | timestamp without time zone | default '2019-01-01 00:00:00'::timestamp without ti
me zone
Indexes:
    "department6_pkey" PRIMARY KEY, btree (deptid)
Distributed by: (deptid)

archdata=#

3.8 自增加

方法一先創建序列，然後設置字段的自增。

create sequence seq_test start with 1 increment by 1 no minvalue no maxvalue cache 1

Sequence(序列)是數據庫經常使用自增列屬性，對於單機PostgreSQL實例，數據庫維護一個自增變量即可。但是對於Greenplum的MPP架構，如果每個節點都維護自己的Sequence，那麼Sequence將會出現重複，那麼Greenplum是如何處理的呢？序列是master統一維護的。

archdata=# create sequence seq_test start with 1 increment by 1 no minvalue no maxvalue cache 1
archdata-# ;
CREATE SEQUENCE

create table tb_test(a int not null default nextval('seq_test'))

方案二使用serial數據烈性

create table tb_test1(a serial not null,b text)

archdata=# \d tb_test1
                         Table "public.tb_test1"
 Column |  Type   |                      Modifiers                       
--------+---------+------------------------------------------------------
 a      | integer | not null default nextval('tb_test1_a_seq'::regclass)
 b      | text    | 
Distributed by: (a)

archdata=#

4 修改表

4.1 修改表名

alter table tb_test1 rename to tb_test_new;

4.2 修改字段名

alter table department rename column createtime to deptcreatetime;

4.3 添加字段

alter table department add column pid int not null;

4.4 刪除字段

alter table department drop column pid;

4.5 刪除表外鍵

首先找出數據庫表的外鍵名稱：

\d [tablename]
....
"table_name_id_fkey" FOREIGN KEY (id) REFERENCES other_table(id) ....
1
2
3
然後使用下面的命令刪除外鍵：

ALTER TABLE [tablename] DROP CONSTRAINT table_name_id_fkey;

5 刪除表

PostgreSQL 使用 DROP TABLE 語句來刪除表格，包含表格數據、規則、觸發器等，所以刪除表格要慎重，刪除後所有信息就消失了。

drop table table_name;

如果想刪除主鍵的表，需要添加cascade，這樣就可以刪除主鍵表，同時刪除了子表的外鍵約束，其他的不會刪除。

6 數據的插入、修改和刪除

6.1 插入

例如，指定要插入的列名和值：
INSERT INTO products (name, price, product_no) VALUES ('Cheese', 9.99, 1);

只指定要插入的值:

INSERT INTO products VALUES (1, 'Cheese', 9.99);


通常，數據值都是常量，但也可以使用標量表達式。例如： 

INSERT INTO films SELECT * FROM tmp_films WHERE date_prod < 
'2016-05-07';


可以在單個命令中插入多行。例如：

INSERT INTO products (product_no, name, price) VALUES
    (1, 'Cheese', 9.99),
    (2, 'Bread', 1.99),
    (3, 'Milk', 2.99);

6.2 更新

UPDATE 命令在一個表中更新行。可以更新一個表中所有的行、所有行的一個子集或者單個行。可以單獨更新每一列而不影響其他列。 

要執行一次更新，需要： 
•要更新的表和列的名稱
•這些列的新值
•指定要更新的行的一個或者更多條件。

例如，下面的命令把所有價格爲5 的產品更新爲價格爲 10: 

UPDATE products SET price = 10 WHERE price = 5;


在Greenplum數據庫中使用 UPDATE 由下列限制:
•GPORCA可以爲Greenplum分佈鍵列提供更新支持，Postgres planner則不會 。
•如果使用了鏡像，不能在UPDATE語句中使用STABLE或VOLATILE 函數。
•Greenplum數據庫的分區列不能被更新.

6.3 刪除數據

DELETE命令從一個表中刪除行。指定一個WHERE子句可以刪除滿足特定條件的行。如果不指定WHERE 子句，該表中所有的行都會被刪除。其結果是一個合法的但爲空的表。例如，從產品表中刪除所有價格爲10的行：

DELETE FROM products WHERE price = 10;


要從一個表中刪除所有行:

DELETE FROM products; 


在Greenplum數據庫中使用 DELETE 具有和使用UPDATE類似的限制:
•如果使用了鏡像，不能在 UPDATE 語句中使用STABLE 或VOLATILE 函數。

Greenplum表的管理實踐-1

Greenplum表的管理實踐-1

文章目錄

1 創建表

2 創建臨時表

2.1 會話級臨時表

2.2 創建會話級別的臨時表

3 約束

3.1 字段級別的check

3.2 表級的check

3.3 非空約束

3.4 唯一約束

3.5 主鍵約束

3.6 外鍵約束

3.7 默認約束

3.8 自增加

4 修改表

4.1 修改表名

4.2 修改字段名

4.3 添加字段

4.4 刪除字段

4.5 刪除表外鍵

5 刪除表

6 數據的插入、修改和刪除

6.1 插入

6.2 更新

6.3 刪除數據

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