Sergey,

Sorry,Ask the wrong question but to check if
"field3 integrity failed " when field2 is EMPTY and field3 is still fill WITH some characters

You can use EMPTY() function.

How to check if field1 is never empty, field2 is empty sometimes that field3 must be empty too ?

mytable.dbf

field1 field2 field3

aaaaaa bbbbbb cccccc
dddddd
eeeeee ffffff ggggggg

a second row with dddddd in field1 should have field2 and field3 empty.

if field3 is not empty

dddddd BLANK kkkkkk(field3)

this row should provide some error message ?

use mytable 

SCAN
*    - "Level 3 integrity failed [class code]" when level 2 is EMPTY and level 3 is fill WITH 123
   
   IF EMPTY(level2) and EMPTY(LEVEL3)

   ANS = MESSAGEBOX(''+CLASSCODE+''+LEVEL1+LEVEL2+LEVEL3, 0, 'LEVEL2 EMPTY BUT LEVEL3 FILL')      
 
   ENDIF
*!*	LOCAL lcAns

*!*	    lcAns= IIF(EMPTY(level2),EMPTY(level3),.T.)
*!*	    
*!*	    ?lcAns
     

ENDSCAN

TIA