sept 2001 cylaufoxpro chapter 61 chapter 6 searching records in a table

Sept 2001 cylau Foxpro Chapter 6 1

Chapter 6

Searching Records in a Table


The LOCATE command

Sequentially searches the table for the first record that matches the specified logical expression.

You say “first”. But “First” in what order?

In the order of whatever “index” is in effect, and in the order of record number if no “index” is in effect.


LOCATE

USE patient Further Practice 5A

LOCATE FOR sex=“F”The record pointer now points to the first

recordstarting from the very beginning of the

table if there are female Patients, and points to (1 + no of the last record) if there are none.


FOUND() and EOF()

USE patientLOCATE FOR sex=“F”? FOUND() output .T. if the desired record is found, output .F. if not found

? EOF() output .F. if the desired record is found,output .T. if not found


CONTINUE

LOCATE get you the first record matching the criteria starting from the beginning of the table.

To find the second one matching the criteria, use the command CONTINUE.


LOCATE & CONTINUE

USE patientLOCATE FOR sex=“F” && recno()=1CONTINUE && recno()=2CONTINUE && recno()=5? FOUND()&& if the output is .T. then

the record pointer is pointing at the third female’s record.


LOCATE & CONTINUE

USE patientLOCATE FOR sex=“F”CONTINUECONTINUELOCATE FOR sex=“F” && recno()=1 again

? FOUND()&& if the output is .T. then the record pointer is pointing at the first female’s record.


Equal or Not equal

Consider the recordPatient_id name dob sex1000 Yin Leonard 12/05/85 MSure enough FoxPro will consider the

criteria sex=“M” is met for this record.But will they consider the criteria

patient_id=“100” being met?It depends.


SET EXACT ON

There are three different sets of rules FoxPro use to judge whether two strings are equal.

For each of the following 3 cases, the set of rules used are all different

SET EXACT ONLOCATE FOR patient_id=‘100’ && recno()=55

SET EXACT OFFLOCATE FOR patient_id=‘100’ && recno()=40

LOCATE FOR patient_id==‘100’ && recno()=55 Note: There are 54 records in the file patient.dbf


== (exactly match)

Insists an exact match:To be considered equal, the two

strings must be of exactly the same length; and

character to character match for the entire string.


SET EXACT ON/OFF

The comparison is character by character.The strings are considered match if a tie

prevail through the end of comparison.The comparison ends either if

a mismatch occurs, (‘1010’ <> ‘100’)

the string on the right is exhausted (SET EXACT OFF) (‘1000’ = ‘100’)

both strings are exhausted (SET EXACT ON)(‘1000’ <> ‘100’)


SORTING

Sorting a table according to the value of a certain expression not only make the table nicer to look at, but also make the searching of a particular record much easier.

However, this process is quite expensive.


SORT a Whole File

USE patient SORT TO newpatient ON sex /DC, dob /AA new .dbf file newpatient will be

created, occupying as many space as patient.dbf

/D : descending/A : ascending/C : case insensitvie


SORTSelected Columns or Rows

USE patient && selected columnsSORT TO newlist ON sex FIELDS name,

sex

USE patient && selected rowsSORT TO youngpatient ON sex;FOR dob>{12/31/1989}


Disadvantages of SORT

Data redundancyUpdate is not automaticSlowConsume disk space

for new file during processing

Complicated procedure to sort original file

Only fields can be sorted, not expressions


INDEX files

An Index file contains only the key expressions and information about where the corresponding record is.

Size is usually much smaller than a separate sorted file.


An Index File

Use patientIndex on name to nameContent of name.idx will look like:Name (key expression) record_numberAu Gertrude 8Au Natalie 37Au Vanessa 50Cheung Quentin 42…Note: size is smaller before only two columns are

stored


Two Types of Index FilesIndependent index file with extension idx

More than one index file may be used An IDX file need to be re-indexed after editing

Compound index file with extension cdx A cdx file should have the same name as the

table. A CDX file may contain more than one index

expression called TAGS. A CDX file will be activated automatically


INDEX ON

USE patientINDEX ON sex TO/TAG sex GO TOP && Sai GertrudeSKIPSKIPAt which record? && Tse Beatrice


A dbf file may have more than one index file

USE patientINDEX ON name TO/TAG nameGO TOP && Au Gertrude SET INDEX/ORDER TO SEX will arrange the data

according to sex instead of name

Can we have descending order of name using index?


SET INDEX / ORDER TO

USE PatientINDEX ON name TO/TAG nameGO TOP && Au GertrudeINDEX ON sex TO/TAG sexGO TOP && Sai GertrudeSET INDEX/ORDER TO nameGO TOP && Au Gertrude SET INDEX/ORDER TO sexGO TOP && Sai Gertrude


FIND and SKIP

USE patientINDEX ON name TAG nameFIND Yeung && Yeung Karen? FOUND() && output .T.SKIP && Yeung Nora


SEEK and SKIP

USE patientINDEX ON name TAG nameSEEK Yeung && variable not

foundSEEK “Yeung” && Yeung Karen? FOUND() && output .T.SKIP && Yeung Nora


UNIQUE

USE patientINDEX ON sex TAG sex2 UNIQUELIST && only one record per sex will be shown

SET ORDER TOLIST && now the index is no longer in effect, so

all records show up

SET ORDER TO sex2LIST && only one record per sex will be shown

again


Macro Substitution &

Macro substitution treats the contents of a variable as a character string literal

Apple=‘patient’ &Apple is the same as ‘patient’

USE Apple && VFP complaints that file doesn’t exist. There is no file with name Apple

USE &Apple && USE patient

List && the contents of patient are shown.


Macro Substitution & (2)USE patient index nameLaw=‘Shut’LOCATE for name=Law && Shut Daphne

LOCATE for name=&Law && variable Shut is not found

LOCATE for name=‘Law’ && Law Beatrice

LOCATE for name=‘&Law’ && Shut Daphne

Note: LOCATE accepts logical expression. Content of variable is used


Macro Substitution & (3)

USE patient index nameLaw=‘Shut’ FIND Law && Law Beatrice FIND &Law && Shut Daphne

FIND ‘Law’ && Law Beatrice FIND ‘&Law’ && Shut Daphne

Note: FIND accepts charstring; name of variable is used, so avoid using variable as

target


Macro Substitution & (4)

USE patient index nameLaw=‘Shut’ SEEK Law && Shut Daphne

SEEK &Law && variable Shut is not found

SEEK ‘Law’ && Law Beatrice

SEEK ‘&Law’ && Shut Daphne

Note: SEEK accepts expressioncontent of variable is used


CompareLOCATE, FIND and SEEK

See p.185


MACRO

A macro records the keystrokesThe key defined for macro should be

a function key<Enter> key is not recorded, have to

type {ENTER}Press Control-A in the Command

Window to launch the macro, select the micro name, then press <enter>

sept 2001 cylaufoxpro chapter 61 chapter 6 searching records in a table

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