Tag Archives: USED()

SELECT

Posted on by vivaclipper

SELECT

Change the current work area

Syntax

      SELECT <xnWorkArea> | <idAlias>

Arguments

<xnWorkArea> is the work area number between 0 and 250 inclusive. This argument is an extended expression and can be specified either as a literal number or as a numeric expression enclosed in parentheses.

<idAlias> is the name of an existing work area to SELECT if there is a database file open in that area.

Description

SELECT is a database command that changes work areas. CA-Clipper supports 250 work areas, with each work area a logical handle to an open database file and all of its attributes. You can refer to work areas with SELECT by number or by alias. The alias of a work area is automatically assigned when a database file is USEd in that work area or by using the ALIAS clause.

Work area 0 refers to the first empty or next available work area. Using this, you can SELECT 0 and USE <xcDatabase> as a method of opening database files.

Notes

. Aliased expressions: Aliased expressions are a much more powerful method of selecting new work areas than the SELECT command. Instead of SELECTing a work area, and then performing an operation for that work area, you can apply an alias to an expression that performs the operation. This is done by specifying the alias of the remote work area and the expression enclosed in parentheses. For example, to access the value of EOF() in an unselected work area, you would normally execute a series of statements like the following:

            SELECT Remote
            ? EOF()
            SELECT Main

Using the aliased expression form, these statements become:

            ? Remote->(EOF())

. USE…NEW: Instead of using SELECT0 and USE <xcDatabase> to open a database file in a new work area, the preferred method is to USE <xcDatabase> NEW.

Examples

      .  This example opens a series of database files by SELECTing
         each work area by number then USEing each database file in that
         work area:

         SELECT 1
         USE Customer
         SELECT 2
         USE Invoices
         SELECT 3
         USE Parts
         SELECT Customer

      .  A better method is to open each database in the next available
         work area by specifying the NEW clause on the USE command line.
          In this example USE...NEW is employed instead of SELECT 0 and
         then USE:

         USE Customer NEW
         USE Invoices NEW

         SELECT Customer

      .  This code fragment changes work areas while saving the current
         work area name to a variable using the SELECT() function.  After
         executing an operation for the new work area, the original work
         area is restored:

         nLastArea := SELECT()
         USE Newfile NEW
         //
         <statements>...
         //
         SELECT (nLastArea)

Seealso

ALIAS(), EOF(), SELECT(), SET INDEX, USE, USED()

Harbour Database Functions

Posted on by vivaclipper

Database Functions

AFields Fills referenced arrays with database field information
Alias Returns the alias name of a work area
BOF Test for the beggining-of-file condition
dbAppend Appends a new record to a database file
dbClearFilter Clears the current filter condiction in a work area
dbCloseAll Close all open files in all work areas.
dbCloseArea Close a database file in a work area
dbCommit Updates all index and database buffers for a given workarea
dbCommitAll Flushes the memory buffer and performs a hard-disk write
dbCreate Creates an empty database from a array
dbDelete Mark a record for deletion in a database
dbEval Performs a code block operation on the current Database
DBF Alias name of a work area
dbFilter Return the filter expression in a work area
dbGoBottom Moves the record pointer to the bottom of the database
dbGoto Position the record pointer to a specific location
dbGoTop Moves the record pointer to the top of the database
dbRecall Recalls a record previousy marked for deletion
dbSeek Searches for a value based on an active index
dbSelectArea Change to another work area
dbSetDriver Establishes the RDD name for the selected work area
dbSetFilter Establishes a filter condition for a work area
dbSkip Moves the record pointer in the selected work area
dbSkipper Helper function to skip a database
dbStruct Builds a multidimensional array of a database structure
dbUseArea Opens a work area and uses a database file
Deleted Tests the record’s deletion flag
EOF Test for end-of-file condition
FCount Counts the number of fields in an active database
FieldDeci Determines the number of decimal places of a given numeric field
FieldGet Obtains the value of a specified field
FieldName Return the name of a field at a numeric field location
FieldPos Return the ordinal position of a field
FieldPut Set the value of a field variable
FieldSize Determines the size of a given field
FieldType Determines the type of a given field
Found Determine the success of a previous search operation
Header Return the length of a database file header
LastRec Returns the number of records in an active work area or database
LUpdate Yields the date the database was last updated
RecCount Counts the number of records in a database
RecNo Returns the current record number or identity
RecSize Returns the size of a single record in an active database
Select Returns the work area number for a specified alias
Used Checks whether a database is in use in a work area

Select()

Posted on by vivaclipper

Select()

Returns the work area number for a specified alias.

Syntax

      Select([<cAlias>]) --> nWorkArea

Arguments

<cAlias> is the target work area alias name.

Returns

Select() returns the work area number.

Description

This function returns the work area number for the specified alias name <cAlias>. If no parameter is specified, the current work area will be the return value of the function.

Examples

      USE tests NEW
      USE names NEW
      cOldArea := Select( "names" )
      SELECT test
      LIST
      SELECT cOldArea

Compliance

Clipper

Files

Library is rdd

Seealso

Alias(), Used()

C5_USED

Posted on by vivaclipper 
 USED()
 Determine whether a database file is in USE
------------------------------------------------------------------------------
 Syntax

     USED() --> lDbfOpen

 Returns

     USED() returns true (.T.) if there is a database file in USE; otherwise,
     it returns false (.F.).

 Description

     USED() is a database function that determines whether there is a
     database file in USE in a particular work area.  By default, USED()
     operates on the currently selected work area.  It will operate on an
     unselected work area if you specify it as part of an aliased expression.

 Examples

     .  This example determines whether a database file is in USE in
        the current work area:

        USE Customer NEW
        ? USED()               // Result: .T.
        CLOSE
        ? USED()               // Result: .F.

 Files   Library is CLIPPER.LIB.

See Also: SELECT SELECT() USE




			

	
	



		
			


	

		
C5 Database Functions


		

		Posted on  by vivaclipper		

	


		

		
AFIELDS() :


Fill arrays with the structure of the current database file


AFIELDS([<aFieldNames>],
    [<aTypes>],
    [<aWidths>],
    [<aDecimals>]) --> nFields


ALIAS() : 


Return a specified work area alias


ALIAS([<nWorkArea>]) --> cAlias


BOF() : 


Determine when beginning of file is encountered


BOF() --> lBoundary


DBAPPEND() : 


Add a new record


DBAPPEND() --> NIL




DBCLEARFILTER() : 


Clear a filter condition


    DBCLEARFILTER() –> NIL


DBCLEARIND() :  Close all indexes for the current work area


    DBCLEARINDEX() --> NIL


DBCLEARREL() : 


Clear active relations


DBCLEARRELATION() --> NIL


DBCLOSEALL() : 


Close all occupied workareas


DBCLOSEALL() --> NIL


DBCLOSEAREA() : 


Close a workarea


DBCLOSEAREA() --> NIL


DBCOMMIT() : 


Flush pending updates


DBCOMMIT() --> NIL


DBCOMMITALL() : 


Flush pending updates in all workareas


DBCOMMITALL() --> NIL


DBCREATE() : 


Create a database file from a database structure array


DBCREATE(<cDatabase>, <aStruct> [, <cDriver> ] ) --> NIL


DBCREATEIND() : 


Create an Index


   DBCREATEINDEX(<cIndexName>, <cKeyExpr>,
        [<bKeyExpr>], [<lUnique>]) --> NIL


DBDELETE() : 


Mark a record for deletion


DBDELETE() --> NIL


DBEDIT() : 


        Browse records in a table layout


    DBEDIT([<nTop>], [<nLeft>],
        [<nBottom>], <nRight>],
        [<acColumns>],
        [<cUserFunction>],
        [<acColumnSayPictures> | <cColumnSayPicture>],
        [<acColumnHeaders> | <cColumnHeader>],
        [<acHeadingSeparators> | <cHeadingSeparator>],
        [<acColumnSeparators> | <cColumnSeparator>],
        [<acFootingSeparators> | <cFootingSeparator>],
        [<acColumnFootings> | <cColumnFooting>]) --> NIL


DBEVAL() : 


Evaluate a code block for each record


DBEVAL(<bBlock>,
    [<bForCondition>],
    [<bWhileCondition>],
    [<nNextRecords>],
    [<nRecord>],
    [<lRest>]) --> NIL


DBF()* : 


Return current alias name


DBF() --> cAlias


DBFIELDINFO() : 


Return and optionally change information about a field


   DBFIELDINFO(<nInfoType>,


        <nFieldPos>,
        [<expNewSetting>]) --> uCurrentSetting


DBFILEGET() : 


Insert the contents of a field into a file


     DBFILEGET(<nFieldPos>, <cTargetFile>, <nMode>)
        --> lSuccess


DBFILEPUT() : 


Insert the contents of a file into a field


     DBFILEPUT(<nFieldPos>, <cSourceFile>)
        --> lSuccess


 DBFILTER() : 


Return the current filter expression as a character string


DBFILTER() --> cFilter


DBGOBOTTOM() : 


Move to the last logical record


DBGOBOTTOM() --> NIL


DBGOTO() : 


Move to a particular record


DBGOTO(<nRecordNumber>) --> NIL


DBGOTOP() : 


Move to the first logical record


DBGOTOP() --> NIL


DBINFO() : 


         Return and optionally change database file information


    DBINFO(<nInfoType>, [<expNewSetting>])
        --> uCurrentSetting


DBORDERINFO() :          Return and optionally change information about orders and index files


    DBORDERINFO(<nInfoType>,   [<cIndexFile>],
        [<cOrder> | <nPosition>],
        [<expNewSetting>]) --> uCurrentSetting


DBRECALL() : 


Reinstate a record marked for deletion


DBRECALL() --> NIL


DBRECORDINFO() :


         Return and optionally change information about a record


    DBRECORDINFO(<nInfoType>,
        [<nRecord>],
        [<expNewSetting>]) --> uCurrentSetting


DBREINDEX() :


         Recreate all active indexes for the current work area


    DBREINDEX() --> NIL


DBRELATION() :


Return the linking expression of a specified relation


DBRELATION( <nRelation> ) --> cLinkExp


DBRLOCK() :      


         Lock the record at the current or specified identity


    DBRLOCK([<xIdentity>]) --> lSuccess


DBRLOCKLIST()          Return an array of the current lock list


   DBRLOCKLIST() --> aRecordLocks


DBRSELECT() :


Return the target workarea number of a relation


DBRSELECT( <nRelation> ) --> nWorkArea


DBRUNLOCK()     


          Release all or specified record locks


    DBRUNLOCK([<xIdentity>]) --> NIL


DBSEEK() : 


Search for a key value


DBSEEK(<expKey>, [<lSoftSeek>]) --> lFound


DBSELECTAR() : 


Change the current workarea


DBSELECTAREA(<nArea> | <cAlias>) --> NIL


DBSETDRIVER() : 


Set the default database driver


DBSETDRIVER([<cDriver>]) --> cCurrentDriver


DBSETFILTER() : 


Set a filter condition


DBSETFILTER(<bCondition>, [<cCondition>]) --> NIL


DBSETINDEX()    


         Empty orders from an order bag into the order list


    DBSETINDEX(<cOrderBagName>) --> NIL


DBSETORDER()


Set the controlling order


    DBSETORDER(<nOrderNum>) --> NIL


DBSETRELAT() :


Relate two workareas


DBSETRELATION( <nArea> | <cAlias>, <bExpr>, [<cExpr>]) --> NIL


DBSKIP() : 


Move relative to the current record


DBSKIP([<nRecords>]) --> NIL


DBSTRUCT() : 


Create an array containing the structure of a database file


DBSTRUCT() --> aStruct


DBUNLOCK()


Release all locks for the current work area


    DBUNLOCK() --> NIL


DBUNLOCKALL()


Release all locks for all work areas


    DBUNLOCKALL() --> NIL


DBUSEAREA() : 


Use a database file in a workarea


DBUSEAREA( [<lNewArea>],
    [<cDriver>],
    <cName>,
    [<xcAlias>],
    [<lShared>],
    [<lReadonly>]) --> NIL


DELETED() : 


Return the deleted status of the current record


DELETED() --> lDeleted


EOF() : 


Determine when end of file is encountered


EOF() --> lBoundary


FCOUNT() : 


Return the number of fields in the current (.dbf) file


FCOUNT() --> nFields




FIELD() : 




Return a field name from the current (.dbf) file




    FIELD/FIELD(<nPosition>) --> cFieldName




FIELDBLOCK() :


Return a set-get code block for a field variable


FIELDBLOCK(<cFieldName>) --> bFieldBlock


FIELDGET() : 


Retrieve the value of a field using the ordinal position of the field in the database structure


FIELDGET(<nField>) --> ValueField


FIELDNAME() : 


Return a field name from the current (.dbf) file


FIELDNAME/FIELD(<nPosition>) --> cFieldName


FIELDPOS() : 


Return the position of a field in a workarea


FIELDPOS(<cFieldName>) --> nFieldPos


FIELDPUT() : 


Set the value of a field variable using the ordinal position of the field in the database structure


FIELDPUT(<nField>, <expAssign>) --> ValueAssigned


FIELDWBLOCK() : 


Return a set-get block for a field in a given workarea


FIELDWBLOCK(<cFieldName>, <nWorkArea>) --> bFieldWBlock




FLOCK() : 


Lock an open and shared database file


    FLOCK() –> lSuccess


FOUND() : 


Determine if the previous search operation succeeded


FOUND() --> lSuccess


HEADER() : 


Return the current database file header length


HEADER() --> nBytes


LASTREC() : 


Determine the number of records in the current (.dbf) file


LASTREC() | RECCOUNT()* --> nRecords


LUPDATE() : 


Return the last modification date of a (.dbf) file


LUPDATE() --> dModification


RECCOUNT()* : 


Determine the number of records in the current (.dbf) file


RECCOUNT()* | LASTREC() --> nRecords


RECNO() : 


Return the current record number of a work area


RECNO() --> nRecord


RECSIZE() : 


Determine the record length of a database (.dbf) file


RECSIZE() --> nBytes


RLOCK()


Lock the current record in the active work area


    RLOCK() --> lSuccess


SELECT() : 


Determine the work area number of a specified alias


SELECT([<cAlias>]) --> nWorkArea


USED() : 


Determine if a database file is in USE


USED() --> lDbfOpen