Creating a table alias (or self join) in Information Designer

You can create a duplicate reference to a database table from Information Designer. This duplicate is called a Table Alias, and references the very same data, only using an alias. This can be useful in certain cases, most often when in need of a self join within a table.

Procedure

In Information Designer, select a table on the Data Sources tab.
Right-click the table and select Create Table Alias.
Type a name for the table alias and click OK.
A table alias of the table is created.

Example: Self joins using a table alias

A self join is a join from a table to itself. In Information Designer, this is implemented by using a table alias.

About this task

The following database table lists a number of employees at a company, and specifies who the manager of each employee is. Carla is the head of the department. Mike and Adrian report directly to Carla, whereas Sarah and Vincent report to Mike.


ID	Name	Manager
1	Sarah	2
2	Mike	3
3	Carla	Null
4	Vincent	2
5	Adrian	3

To produce a list where the ID stated in the Manager column is replaced by a name, we would need a self join in the table. The table needs to look up the ID column in itself.


Name	Manager
Sarah	Mike
Mike	Carla
Carla
Vincent	Mike
Adrian	Carla

Procedure

To perform a self join as described above, first create a Table Alias of the table.
Create a join between the table and its alias:
```
WHERE TABLE.ID=TABLE_ALIAS1.MANAGER
```