FILTER Example

FILTER Examples

Example 1 - Simple filtering

IFILE	IFILE
KEY	INIT	"mykey"
.
	OPEN	IFILE,...
	...
	FILTER	IFILE,"CompanyName = 'Sunbelt' AND ID = 10"
or
	FILTER	IFILE,"CompanyName LIKE '%bel%'"

The first FILTER statement limits the data retrieved from the ISAM file to records containing a company name of "Sunbelt" and and ID value of 10. The second FILTER statement limits the ISAM file to records that have a company name containing the string "bel".

Example 2 - Using 'SKIPKEYS=nnn' keyword option

IFILE	IFILE
ONE	INTEGER	1,"1"
.
	OPEN	IFILE,"test"
.
	FILTER	IFILE,"",SKIPKEYS=ONE
	LOOP
	READKS	IFILE;S$CMDLIN
	UNTIL	OVER
	DISPLAY	"Data:",*LL,S$CMDLIN
	REPEAT
.
	FILTER	IFILE;S$CMDLIN //Clears all filtering!
	...

In this example, every other record is skipped.

Example 3 - Using '$SKIPKEYS$[nnn]' string name operator

...

IFILE	IFILE
.
	OPEN	IFILE,"test"
.
	FILTER	IFILE,"$SKIPKEYS$[1]"
	LOOP
	READKS	IFILE;S$CMDLIN
	UNTIL	OVER
	DISPLAY	"Data:",*LL,S$CMDLIN
	REPEAT
.
	FILTER	IFILE;S$CMDLIN //Clears all filtering!

In this example, every other record is skipped.

Example 4 - Using 'SKIPKEYS=nnn' keyword option

. Read IFILE KEY to position in ISI file key tree.
. Set SKIPKEYS keyword to skip 20 keys for every READKS.
. After first READKS, clear the skip count to read
. every record after the first 20 keys have been skipped.
.
IFILE	IFILE
KEY	DIM	10
.
	OPEN	IFILE,"test"
	MOVE	"SOMEKEY",KEY
	READ	IFILE,KEY;S$CMDLIN // Position to ISI Key
.
	FILTER	IFILE, "", SKIPKEYS=20 // Set to skip 20 ISI keys
	LOOP
.
. Read IFILE KEY to position in ISI file key tree.
. Set SKIPKEYS keyword to skip 20 keys for every READKS.
. After first READKS, clear the skip count to read
. every record after the first 20 keys have been skipped.
.
	READKS	IFILE;S$CMDLIN
	UNTIL	OVER
	DISPLAY	"Data:",*LL,S$CMDLIN
.
. After the first 20 keys have been, the skip count is cleared
. to allow every ISI key to be accessed.
.
	FILTER	IFILE,"", SKIPKEYS=0 // Explicitly clear skip count
	REPEAT
.

Example 5 - Using '$SKIPKEYS$[nnn]' string name operator

. Read IFILE KEY to position in ISI file key tree.
. Set $SKIPKEYS$ to skip 20 keys for every READKS.
. After first READKS, clear the skip count to read
. every record after the first 20 keys have been skipped.
.
IFILE	IFILE
KEY	DIM	10
.
	OPEN	IFILE,"test"
.
	MOVE	"SOMEKEY",KEY
	READ	IFILE,KEY;S$CMDLIN // Position to ISI key
.
	FILTER	IFILE, "$SKIPKEYS$[20]" // Set to skip 20 ISI keys
	LOOP
.
. This READKS skips 20 ISI keys and returns the record for
. the 21 key. An OVER can be returned if skip count is larger
. than the number of keys the remain in the ISI tree.
.
	READKS	IFILE;S$CMDLIN
	UNTIL	OVER
	DISPLAY	"Data:",*LL,S$CMDLIN
.
. After the first 20 keys have been, the skip count is cleared
. to allow every ISI key to be accessed.
.
	FILTER	IFILE,"$SKIPKEYS$[0]" // Explicitly clear skip count
	REPEAT
.

Example 6 - Using 'SKIPONCE=nnn' keyword option

. Set SKIPONCE keyword to skip count 1 key (First key!)
. Read IFILE by KEY using a skip count.
. This example checks for a duplicate key in a single read operation.
.
IFILE	IFILE
KEY	DIM	10
.
	OPEN	IFILE,"test"
.
	FILTER	IFILE, "", SKIPONCE=1 // Set to skip 1st key!
.
	MOVE	"ValidKey",Key
	READ	IFILE,KEY;S$CMDLIN // Reading with SKIPONCE Filter
		// Skip count cleared after read
	IF	OVER
	DISPLAY	"No duplicate key!"
	ELSE
	DISPLAY	"Duplicate key exists!"
	ENDIF

Example 7 - Using '$SKIPKEYS$[nnn]' string name operator

. Set SKIPONCE keyword to skip count 1 key (First key!)
. Read IFILE by KEY using a skip count.
. This example checks for a duplicate key in a single read operation.
.
IFILE	IFILE
KEY	DIM	10
.
	OPEN	IFILE,"test"
.
	FILTER	IFILE, "$SKIPONCE$[1]" // Set to skip 1st key!
.
	MOVE	"ValidKey",Key
	READ	IFILE,KEY;S$CMDLIN // Reading with SKIPONCE Filter
		// Skip count cleared after read
	IF	OVER
	DISPLAY	"No duplicate key!"
	ELSE
	DISPLAY	"Duplicate key exists!"
	ENDIF