【IT168 技术】本操作目的是为PostgreSQL数据库在不同模式之间迁移数据，可用于在异机数据迁移的场景。
某网友曾经问到一个问题，是在数据迁移的场景中，想把源库的数据迁移到不同的schema下面，比如从schema gaoqiang，迁移到schema mayday。
schema(模式)这种概念在Oracle中，可以把用户认为就是schema，比如用户gaoqiang的模式就是gaoqiang;在其他数据库中不一定是一一严格对应的，具有一定的灵活性。在PostgreSQL数据库中，模式和用户可以单独创建，也可一起创建。
操作思路：
从备份导出原有的schema gaoqiang的数据--->新建用户、模式 mayday--->修改相关配置--->导入数据到新的模式Mayday--->验证数据完整性以及属性
导出数据库music中的模式gaoqiang的表结构和数据：
-bash-4.1$ pg_dump -d music -n gaoqiang -f /tmp/gaoqiang.sql
-bash-4.1$ cat gaoqiang.sql
--
-- PostgreSQL database dump
--
SET statement_timeout = 0;
SET lock_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SET check_function_bodies = false;
SET client_min_messages = warning;
--
-- Name: gaoqiang; Type: SCHEMA; Schema: -; Owner: gaoqiang
--
CREATE SCHEMA gaoqiang;
ALTER SCHEMA gaoqiang OWNER TO gaoqiang;
SET search_path = gaoqiang, pg_catalog; ----标红的2行一个是决定导入到那个schema中，一个是决定表的属性，还可以设定表空间和oid，如果有需要可以设置
SET default_tablespace = '';
SET default_with_oids = false;
--
-- Name: summary; Type: TABLE; Schema: gaoqiang; Owner: gaoqiang; Tablespace:
--
CREATE TABLE summary (
id integer,
name text
);
ALTER TABLE summary OWNER TO gaoqiang;
--
-- Data for Name: summary; Type: TABLE DATA; Schema: gaoqiang; Owner: gaoqiang
--
COPY summary (id, name) FROM stdin;
1 GaoQiang
2 GaoQiang is not 2
\.
--
-- PostgreSQL database dump complete
--
创建新的用户和模式：
music=# \c music postgres
You are now connected to database "music" as user "postgres".
music=# create user mayday with password 'mayday';
CREATE ROLE
music=# create schema authorization mayday;
CREATE SCHEMA
修改pg_dump导出的文件gaoqiang.sql：
把原来的：
SET search_path = gaoqiang, pg_catalog;
改成：
SET search_path = mayday, pg_catalog;
-bash-4.1$ vi gaoqiang.sql
-bash-4.1$ cat gaoqiang.sql |grep mayday
SET search_path = mayday, pg_catalog;
开始迁移:
-bash-4.1$ psql music
SET
SET
SET
SET
SET
SET
ERROR: schema "gaoqiang" already exists
ALTER SCHEMA
SET
SET
SET
CREATE TABLE
ALTER TABLE
COPY 2
-bash-4.1$
用mayday登录数据库查看表的属性：
-bash-4.1$ psql music mayday
psql (9.4.1)
Type "help" for help.
查看表属性：
music=> \d
List of relations
Schema | Name | Type | Owner
--------+---------+-------+----------
mayday | summary | table | gaoqiang ---发现该表的属主属性有点问题
(1 row)
处理方法有2种，都很简单：
方法1：
-bash-4.1$ psql music postgres
psql (9.4.1)
Type "help" for help.
music=# alter table mayday.summary OWNER TO mayday;
ALTER TABLE
music=# \c music mayday
You are now connected to database "music" as user "mayday".
music=> \d
List of relations
Schema | Name | Type | Owner
--------+---------+-------+--------
mayday | summary | table | mayday
(1 row)
方法2：
先删除刚才的测试表，然后再进行导入操作，避免冲突：
music=> drop table summary;
DROP TABLE
在导出的脚本中有这么一行：
ALTER TABLE summary OWNER TO gaoqiang;
在修改模式路径的时候，直接修改该语句也可。
-bash-4.1$ vi /tmp/gaoqiang.sql
ALTER TABLE summary OWNER TO mayday;
music=> \d
List of relations
Schema | Name | Type | Owner
--------+---------+-------+----------
public | summary | table | postgres
(1 row)
music=> \q
开始迁移：
-bash-4.1$ psql music
SET
SET
SET
SET
SET
SET
ERROR: schema "gaoqiang" already exists
ALTER SCHEMA
SET
SET
SET
CREATE TABLE
ALTER TABLE
COPY 2
-bash-4.1$
验证表的属主和模式已改变：
-bash-4.1$ psql music mayday
psql (9.4.1)
Type "help" for help.
music=> \d
List of relations
Schema | Name | Type | Owner
--------+---------+-------+--------
mayday | summary | table | mayday
(1 row)
验证数据完整性与属性：
用DBA用户连接数据库查询2张不同模式的表：
music=> \c music postgres
You are now connected to database "music" as user "postgres".
music=# select * from gaoqiang.summary;
id | name
----+-------------------
1 | GaoQiang
2 | GaoQiang is not 2
(2 rows)
music=# select * from mayday.summary;
id | name
----+-------------------
1 | GaoQiang
2 | GaoQiang is not 2
(2 rows)
music=# \c music gaoqiang
You are now connected to database "music" as user "gaoqiang".
music=> \d
List of relations
Schema | Name | Type | Owner
----------+---------+-------+----------
gaoqiang | summary | table | gaoqiang
(1 row)
music=# select tablename,tableowner,schemaname from pg_tables where tablename = 'summary';
tablename | tableowner | schemaname
-----------+------------+------------
summary | gaoqiang | gaoqiang
summary | mayday | mayday
(4 rows)
至此，迁移已经全部完成。
