The WHERE Clause

The QueryExp class is an abstract class whose subclasses represent conditional expressions which return a boolean value when a particular CIMInstance is applied to them.

The WHERE clause narrows the scope of a query. The WHERE clause contains a conditional expression, which can contain a property or key word, an operator, and a constant. All WHERE clauses must specify one of the predefined WQL operators.

The basic syntax for a WHERE clause appended to a SELECT statement follows:

The conditional expression in a WHERE clause takes the following form:

 
property operator constant

The following subclasses of the QueryExp class manipulate particular types of conditional expressions in the WHERE clause:

• AndQueryExp

• BinaryRelQueryExp

• NotQueryExp

• OrQueryExp

The conditional expression in the WHERE clause is represented by the QueryExp class. A conditional expression is represented by a tree structure. For example, the conditional expression (a=2 and b=3 or c=4) is represented by the tree structure shown in the following figure:

The QueryExp class returns only the top level of the query expression tree. In the above example, an OR QueryExp. The provider can then use methods within that class to get branches down the query expression tree.