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WHERE Clause

Use the WHERE clause to narrow the scope of a data, event, or schema query. For more information, see Querying with WQL. The WHERE clause is made up of a property or keyword, an operator, and a constant. All WHERE clauses must specify one of the predefined operators that are included in the Windows Management Instrumentation (WMI) Query Language (WQL). You can append the WHERE clause to the SELECT statement using one of the following forms:


SELECT * FROM class WHERE property operator constant
SELECT * FROM class WHERE constant operator property

where * is the item queried about, class is the class in which to query, and constant, operator, and property are the constant, operator, and property or keyword to use. For more information about the SELECT statement, see SELECT Statement for Data Queries, SELECT Statement for Event Queries, or SELECT Statement for Schema Queries.

The value of the constant must be of the correct type for the property. Moreover, the operator must be among the list of valid WQL operators. Either a property name or a constant must appear on either side of the operator in the WHERE clause.

You may use string literals, such as "NTFS", in a WHERE clause. If you wish to include the following special characters in your string, you must first escape the character by prefixing the character with a backslash (\):

  • backslash (\\)
  • double quotes (\")
  • single quotes (\')

Arbitrary arithmetic expressions cannot be used. For example, the following query returns only the instances of the Win32_LogicalDisk class that represent NTFS drives:


SELECT * FROM Win32_LogicalDisk WHERE FileSystem = "NTFS"

Property names cannot appear on both sides of the operator. The following query is an example of an invalid query:


SELECT * FROM PhysicalDisk WHERE Partitions < (4 + 7 - 2) 
    OR   (Partitions = SectorsPerTrack / 7)

For most uses of class descriptors in a WHERE clause, WMI flags the query as invalid and returns an error. However, use the dot (.) operator for properties of type object in WMI. For example, the following query is valid if Prop is a valid property of MyClass and is type object:

SELECT * FROM MyClass WHERE Prop.embedprop = 5

Comparison tests are always case-insensitive. That is, the following three statements all evaluate to TRUE:


SELECT * FROM MyClass WHERE Prop1 = "cat"
SELECT * FROM MyClass WHERE Prop1 = "CAT"
SELECT * FROM MyClass WHERE Prop1 = "cAt"

You can construct a query that includes Boolean data types, but the only valid Boolean operand types are the =, != and <> types. The value TRUE is equivalent to the number 1, and the value FALSE is equivalent to the number 0. The following examples are of queries that compare a Boolean value against the values TRUE or FALSE.


SELECT * FROM MyClass WHERE BoolProp = 1
SELECT * FROM MyClass WHERE BoolProp = TRUE
SELECT * FROM MyClass WHERE BoolProp <> FALSE
SELECT * FROM MyClass WHERE BoolProp = 0
SELECT * FROM MyClass WHERE BoolProp = FALSE
SELECT * FROM MyClass WHERE BoolProp != 1
SELECT * FROM MyClass WHERE BoolProp != FALSE
SELECT * FROM MyClass WHERE BoolProp <> FALSE

The following examples are of invalid queries that attempt to use invalid operands.


SELECT * FROM MyClass WHERE BoolProp <= TRUE
SELECT * FROM MyClass WHERE BoolProp >= 0
SELECT * FROM MyClass WHERE BoolProp > FALSE
SELECT * FROM win32_computersystem WHERE infraredsupported >= null

Multiple groups of properties, operators, and constants can be combined in a WHERE clause using logical operators and parenthetical subexpressions. Each group must be joined with the AND, OR, or NOT operators as is shown in the following queries. The first query retrieves all instances of the Win32_LogicalDisk class with the Name property set to either C or D:


SELECT * FROM Win32_LogicalDisk WHERE Name = "C:" OR Name = "D:"

The second query retrieves disks named "C:" or "D:" only if they have a certain amount of free space remaining and have NTFS file systems:


SELECT * FROM Win32_LogicalDisk WHERE (Name = "C:" OR Name = "D:") 
    AND  FreeSpace > 2000000  AND   FileSystem = "NTFS"

This example shows a schema query using the WHERE clause.


SELECT * FROM meta_class WHERE __this ISA "myClassName"

The class meta_class identifies this as a schema query, the property called __this identifies the target class of the query and the ISA operator requests definitions for the subclasses of the target class. Therefore, the preceding query returns the definition for the myClassName class and definitions for all of its subclasses.

The following example is a data query using the ASSOCIATORS OF statement with WHERE:


ASSOCIATORS OF {myClass.keyVal="Value1"} WHERE ClassDefsOnly

The next example shows a schema query using ASSOCIATORS OF and WHERE:


ASSOCIATORS OF {myClass} WHERE SchemaOnly

The following example is a data query using the REFERENCES OF statement and WHERE:


REFERENCES OF {myClass.keyVal="Value1"} 
    WHERE RequiredQualifier = myQual

This last example is a schema query using REFERENCES OF and WHERE:


REFERENCES OF {myClass} WHERE SchemaOnly

In addition to the WMI DATETIME format, the WQL WHERE clause supports several other date and time formats:

 

 

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