True and False

PQL recognizes TRUE and FALSE as reserved words that operate in the same way as in SQL, by adding a true or false condition to the clause in which they are used. You can use them to provide a condition to an otherwise conditionless node, to avoid Merge Rule 1.

Wherever you can use an expression that has a strictly Boolean result (true or false), you can also use the terms TRUE or FALSE. And since Boolean is a PQL type, you can also use TRUE or FALSE in an assignment or a test. For example, TRUE and FALSE can be used in the following situations:

MERGE into / values { foo => true  }

SELECT .. FROM .. WHERE shared = true order by 1

TRUE

When used with the MERGE statement, as in the following example, TRUE provides a condition for a node that is otherwise conditionless, and thus avoids Merge Rule 1, which dictates that if the server finds no conditions on a node, it replaces all existing nodes with that name:

MERGE INTO / values {
  network [TRUE] => {
    device[interface/mac_address = '00:00' or 
    interface/ip_address = '1.2.3.4'] => {
      interface => {
        name => 'eth0', 
        mac_address => '00:B1:B2:B3:B4:B5', 
        ip_address => '10.10.10.40'
      }
    }
  }
}

Since the top-level network node normally does not have any conditions, we need an exception for this node, or the MERGE statement will follow Rule 1 and replace the entire tree every time we run a MERGE statement. The condition of [TRUE] provides that exception.

This statement updates the network tree, rather than replacing it, because the use of [TRUE] provides an exception from Merge Rule 1. This particular example is explained in more detail on the Merge page.

FALSE

When used with the MERGE statement, as in the following example, FALSE provides a way to force Merge Rule 2 and ensure new node creation. For example, you can add a [FALSE] condition to log messages so that GoToAssist adds new log nodes instead of updating existing ones:

 MERGE INTO / values {
   log [FALSE] => {
     message => 'Service started', 
     timestamp => '1/2/07'
   }
 } 

This statement creates a new log, rather than updating an existing log:

row: 
    *: 
     log: 
       timestamp: 1/2/07
       message: Service started

For more details about this particular example, see Example of Merge Rule 2.

Example 1: Using TRUE in the predicate

In this example, TRUE is used in the WHERE clause to limit the query to find shared printers only. To broaden the query to include information about printers that are not shared, remove the entire WHERE clause.

This query gathers information about shared printers for which GoToAssist has WMI information, which helps tracks workload per printer, inventory, and troublehooting.

MERGE INTO / VALUES {
 apps[true] => {
  com[true] => {
   paglo[true] => {
    crawlers[true] => {
     crawler[guid = '00132034F4AC'] => {
      plugins[true] => {
       plugin[name = 'snmp_interface_statistics'] => {
        enabled[true] => 'true'
       }
      }
     }
    }
   }
  }
 }
}

If you run this MERGE statement in the Sandbox, the result looks like this:

row
   *
     apps
       com
         paglo
           crawlers
             crawler
               plugins
                 plugin
                   enabled: true 

Example 2: Using TRUE in the predicate

In this example, TRUE is used in the WHERE clause to limit the query to find shared printers only. To broaden the query to include information about printers that are not shared, remove the entire WHERE clause.

This query gathers information about shared printers for which GoToAssist has WMI information, which helps tracks workload per printer, inventory, and troubleshooting.

SELECT systemname as "Printer Host",
  name as "Share Name",
  location as "Location",
  default as "Default",
  portname as "Printer Port",
  drivername as "Driver",
  published as "Published",
  printerstatus as "Status",
  local as "Local Printer",
  docompletefirst as "Print Spooled First",
  capabilitydescriptions as "Capabilities",
  horizontalresolution as "Hor. Resolution",
  verticalresolution as "Vert. Resolution",
  shared as "Shared",
  printprocessor as "Print Processor" 
FROM /network/device/wmi/win32_printer
WHERE shared = 'true' order by 1

Depending on the network, the results of this query will look similar to these:

row
  Printer Host AMSTERDAM
  Share Name DYMO LabelWriter 320
  Location
  Default
  Printer Port USB888
  Driver DYMO LabelWriter 320
  Published true
  Status 3 Idle
  Local Printer true
  Print Spooled First true
  Capabilities Copies, Color, Collate
  Hor. Resolution 300 Pixels per Inch
  Vert. Resolution 300 Pixels per Inch
  Shared true
  Print Processor WinPrint
row
  Printer Host OAXACA
  Share Name printer-copier
  Location Copy Room
  Default
  Printer Port IP_10.10.10.10
  Driver LANIER 5627 PCL 6
  Published true
  Status 3 Idle
  Local Printer true
  Print Spooled First true
  Capabilities Copies, Color, Duplex, Collate
  Hor. Resolution 600 Pixels per Inch
  Vert. Resolution 600 Pixels per Inch
  Shared true
  Print Processor WinPrint
  . . .

Example 3: User environment variables

This example uses a search template to provide a list of hosts to choose from. Run the query, select a host, and the results display the variables for that host.

As in the previous example, this example includes TRUE in the WHERE clause to limit the query.

SELECT caption as "Variable",
  username as "User",
  variablevalue as "Environment Value"
FROM /network/device/wmi/win32_environment
WHERE ../win32_operatingsystem/csname = 
  '[[1param|Windows Hosts|select csname 
  from /network/device/wmi/win32_operatingsystem 
  where csname is not null]]' 
AND systemvariable != 'true'

Depending on the network, the results of this query will look similar to this:

row
   Variable: NT AUTHORITY\SYSTEM\TEMP
   User: NT AUTHORITY\SYSTEM
   Environment Value: %USERPROFILE%\Local Settings\Temp
row
   Variable: NT AUTHORITY\SYSTEM\TMP
   User: NT AUTHORITY\SYSTEM
   Environment Value: %USERPROFILE%\Local Settings\Temp
row
   Variable: NT AUTHORITY\LOCAL SERVICE\TEMP
   User: NT AUTHORITY\LOCAL SERVICE
   Environment Value: %USERPROFILE%\Local Settings\Temp 
  . . .

If you change the != 'true' to = 'true', the results of this query will look similar to this:

row
   Variable: \APR_ICONV_PATH
   User: 
   Environment Value: C:\Program Files\Subversion\iconv
row
   Variable: \ClusterLog
   User: 
   Environment Value: C:\WINDOWS\Cluster\cluster.log
row
   Variable: \ComSpec
   User: 
   Environment Value: %SystemRoot%\system32\cmd.exe  
  . . .

Related topics

• Expressions
• Functions
• Operators
• Read about PQL?

| Views: 1260 | Last Updated: Thu, May 09 2013 2:28 PM

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