Describing Screening Conditions

Topics: Relational Operators Logical Operators

So far, you have written report requests that retrieve all records available in the EMPLOYEE data source for the fields you specify. Using the WHERE keyword, you can limit the records retrieved by specifying conditions a record must meet in order to be retrieved.

You use WHERE to begin a conditional statement. You create a condition by comparing a field or calculation to a test value, another field, or a calculation you supply. You can include several conditions in a single request.

You create a conditional statement using the following format:

WHERE field relational_operator {test_value|field|calculation}[;]         

In the above structure, if you supply a test value, it is the value to which each record is compared. If you supply a field, it can be alphanumeric or numeric as long as the data type is the same as the field name to the left of the relational operator. If you supply a calculation, it can be a mathematical formula or alphanumeric manipulation.

The relational operator enables you to determine the type of comparison between the field and any of the components to the right of the operator. When the value is retrieved from the data source, it checks each value to see if it meets the condition you specified. Only values that satisfy the condition or conditions are included in the report. To retrieve values that do not satisfy conditions, use the NOT operator in front of the expression.

When you include WHERE in your request to describe screening conditions, remember the following rules:

• Make sure the field or fields you are screening and the test values or fields to which you are comparing them to are the same data type. That is, they must both be either numeric or alphanumeric.
• Enclose all literal test values that are alphanumeric in single quotation marks ('). The literal test value is the string of characters searched for in each record.

Note: You can include screening conditions in a procedure, Master File, or filter file.