Boolean Expressions

• Syntax
• Description
• Examples
• Expressions
• Functions
• Operators

Syntax

Use boolean_expressions with operators such as <, >, =, and so on, to set limits, thresholds, or filters on query results. The possible elements of a boolean_expression include:

boolean_expression ::= ( boolean_expression )
boolean_expression ::= boolean_expression AND boolean_expression
boolean_expression ::= boolean_expression OR boolean_expression
boolean_expression ::= NOT boolean_expression
boolean_expression ::= expression = expression
boolean_expression ::= expression != expression | expression <> expression
boolean_expression ::= expression > expression
boolean_expression ::= expression < expression
boolean_expression ::= expression >= expression
boolean_expression ::= expression <= expression
boolean_expression ::= expression                            IS NULL
boolean_expression ::= expression                            IS NOT NULL
boolean_expression ::= expression LIKE STRING
boolean_expression ::= expression LIKE REGEX
boolean_expression ::= expression = REGEX
boolean_expression ::= REGEX = expression
boolean_expression ::= TRUE
boolean_expression ::= FALSE

The boolean_expression returns a Boolean value — that is, an either-or result such as True or False. Where the value of the boolean expression is unknown, null is returned.

 

Description

PQL recognizes the standard SQL-type boolean values of true, false, or unknown, represented by null. Boolean expressions are often used in the WHERE clause with operators such as <, >, =, and so on, to set limits, thresholds, or filters on query results.

Examples

• Example 1: Free space below 1 GB
• Example 2: Hard disk used space
• Example 3: Local drives

Example 1: Free space below 1 GB

Query: What devices have free disk space that is less than 1 GB?

SELECT systemname, name, description, 
  format(freespace, 'human_bytes') 
FROM %free disk space% 
WHERE freespace < 1000000000 
AND description = 'Local Fixed Disk'

This query finds all machines with free disk space under 1 GB. The query uses a boolean expression in the WHERE freespace < 1000000000 clause to indicate a free space threshold.

Results: Depending on the database, this query returns results similar to this:

row
   systemname LUXEMBURG
   name C:
   description Local Fixed Disk
   format(freespace, human_bytes)
     freespace 233.05 MB
row
   systemname ROME
   name D:
   descriptionLocal Fixed Disk
   format(freespace, human_bytes)
     freespace 176.97 MB
row
   systemname PARIS-VM-XP
   name C:
   description Local Fixed Disk
   format(freespace, human_bytes)
     freespace 318.95 MB  
   . . .

Example 2: Hard disk used space

Query: How much disk space is used on devices of drive type 3?

SELECT systemname||' '||name, size, 
  (size -freespace) as "Used Space"
FROM /network/device/wmi/win32_logicaldisk 
WHERE drivetype = 3

his query creates a graph of local hard disk size and the used disk space on it, obtained via the Windows Management Instrumentation (WMI) tool. The query uses a boolean expression in the WHERE drivetype = 3 clause to limit the results to a single drive type.

Results: Depending on the database, this query returns results similar to this:

row
   systemname || || name SATURN D:
   size 500055896064 Bytes
   Used Space 216723492864
row
   systemname || || name JUPITER C:
   size 76100288512 Bytes
   Used Space 14057734144
row
   systemname || || name MERCURY C:
   size 12889010176 Bytes
   Used Space 9776181248  
   . . .

Example 3: Local drives

Query: List my drives and pertinent information about them.

SELECT systemname as "Machine Name",
  name as "Drive",
  description as "Label",
  drivetype as "Type",
  filesystem as "File System",
  volumeserialnumber as "Serial Number",
  format(size, 'human_bytes') as "Total Space",
  format(freespace, 'human_bytes') as "Free Space",
  format(size - freespace, 'human_bytes') as "Used Space",
  format((100 * freespace) / size, 'human_bytes')||'%' as 
  "% Free"
FROM /network/device/wmi/win32_logicaldisk 
WHERE description != 'Network Connection' order by 1,2

This query displays a list of disk and CD Rom drives obtained via the Windows Management Instrumentation (WMI) tool. The query uses a boolean expression in the WHERE description != 'Network Connection' clause to filter out drives described as network connections.

Results: Depending on the database, this query returns results similar to this:

row
   Machine Name AS01-THMS232-ASB
   Drive C:
   Label Local Fixed Disk
   Type 3 Local Disk
   File System NTFS
   Serial Number E433125D
  Total Space
     size 37.18 GB
  Free Space
     freespace 8.88 GB
   Used Space 28.30 GB
   % Free 23%
row
   Machine Name AS01-THMS232-ASB
   Drive D:
   Label CD-ROM Disc
   Type 5 Compact Disc
   File System
   Serial Number
  Total Space
     size
  Free Space
     freespace
   Used Space null
   % Free null   
   . . .

Related topics

• Functions
• Operators
• Expressions
• Read about PQL

| Views: 1557 | Last Updated: Thu, May 09 2013 2:28 PM

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