Understanding Visual Where

Visual Where shows your Where statement in a visual format. The following examples will help you understand how this is displayed.

Example 1

WHERE LOCATION = '234'

AND MGRNO is not null

This Where statement has 2 conditions. The database will return rows for which both conditions are met.

Visual Where will show this visually as per the diagram below.

The database will test every row against the conditions in the Where statement

• each yellow box is a condition to be tested
• if a condition is True, continue to the next condition.
• if a condition is False, the path terminates and the row will not be displayed.
• if you get to the Result node, the row will be returned by the query

In this example:

• the condition LOCATION='234' is tested
• if successful, MGRNO is not null, is then tested
• if successful, the row will be returned in the result
• if neither condition is successful, the row will not be included in the result

Example 2

WHERE (LOCATION = '234' OR LOCATION = '123')

AND MGRNO is not null

This is similar to previous Where statement, except that there are two conditions on LOCATION. A row will be displayed if either LOCATION='234' or LOCATION='123' (and MGRNO is not null).

Visual Where will show this visually as below. There are now two routes that can be taken to the Result node. If the LOCATION='234' test fails, then LOCATION='123' offers another route through to Result.

Example 3

This is a more complex Where statement with many conditions. However the same rule applies as per with the previous examples - if there is a route through to Result then the row will be displayed, otherwise it will not.