The queries in Example 5 11 shows how it works

Example 5 11   Multiple database example

mysql>create database itsodb_1;

mysql>create database itsodb_2;

mysql>connect itsodb_1;

mysql>create table itso1(col1 int, col2 char(10));

mysql>insert into itso1 values(1, itso );

mysql>connect itsodb_2;

mysql>create table itso2(col1 int, col2 char(10));

mysql>insert into itso2 values(1, itso1 );

mysql>select * from itso2,itsodb_1.itso1;

This works in MySQL and give result

+      +       +      +      +

| col1 | col2  | col1 | col2 |

+      +       +      +      +

|    1 | itso1 |    1 | itso |

|    1 | itso1 |    2 | itso |

+      +       +      +      +

Figure 5 5 shows the architecture of multiple MySQL databases accessed by 

single application using same connection.

My

My

SQL

SQL

S

S

e

e

r

r

ver

ver

Access Tables

using 

Qualified Name

Application1

Connection 1

MySQL

MySQL

Database1

Database2

Figure 5 5   MySQL Application with multiple DBs instead of multiple schemas

DB2 UDB supports multiple database access with database links in a federated 

system. For a none federated system, DB2 UDB application uses more logical 

technique by using multiple schemas in place of multiple database used in same 

application. Each database can have multiple schemas and each table belongs 

to a particular schema. 

When migrating the MySQL applications using multiple databases, all the 

databases used in the applications can be placed under one DB2 UDB database. 

 Chapter 5. Database porting 

109