Question

I have a query which retrieve from few tables but 2 tables having same field value,

Query is

SELECT A.NUM_RIF, B.NDG, D.NDG FROM ICGR1100 A 
LEFT JOIN (ICGR1105 E INNER JOIN ICGR1101 D ON E.C_IST=D.C_IST AND E.DT_DOM_NDG=D.DT_DOM_NDG AND E.N_DOM=D.N_DOM) ON A.C_IST=E.C_IST AND A.NUM_RIF=E.NUM_RIF 
LEFT JOIN ICGR1103 B ON A.C_IST=B.C_IST AND A.NUM_RIF=B.NUM_RIF

Result is:

NUM_RIF           NDG               NDG              
 ----------------  ----------------  ---------------- 
0000000000000981  (null)            0000000000002490 
0000000000000985  (null)            0000000000002490 
0000009000004523  0000000000001775  (null)                   
0000009000004521  0000000000001775  (null)           
0000009000004218  0000000000001775  (null)           
0000000000000980  (null)            (null)           
0000009000004914                    0000000000002490 
0000009000004917                    
0000009000004923                    0000000000002490 

So my expectation result is as below:

NUM_RIF           NDG                           
 ----------------  ---------------- 
0000000000000981  0000000000002490 
0000000000000985  0000000000002490 
0000009000004523  0000000000001775                 
0000009000004521  0000000000001775           
0000009000004218  0000000000001775          
0000000000000980  (null)                   
0000009000004914  0000000000002490 
0000009000004914  
0000009000004923  0000000000002490 

the case is both field might have empty value, or null, or either one will be empty/null, but so far don’t have value in both field, which mean only one field have value

Answer 1

Most dbmss have a NVL like function:

NVL(B.NDG, D.NDG) as NDG

Will return B.NDG if not null otherwise D.NDG

NVL is for Oracle but there’s probably an equivalent for your dbms