CASE and JOIN Query Help

Question

I have two Tables
Table A
ID                             VALUE           
1                         Delhi                
2                      Mumbai                
3                      Bangalore
Table B
TYPE                        TYPE_A_ID                         TYPE_B_ID             
A                      1                                 NA                   
A                      1                                 NA                
B                      NA                                2           
A                      3                                 NA                  
B                      NA                                    1                   
A                      1                                 NA            I want to get the value from Table A, depending on the Type in Table B
i.e., when the Type is A, the value in Type_A_ID should be looked up in Table A
and when the Type is B, the value in Type_B_ID should be looked up in Table A.
The result how i need is as follows:
TYPE                        TYPE_A_ID                         TYPE_B_ID                 Value      
A                         1                                 NA                     Delhi
A                      1                                 NA                     Delhi
B                      NA                                2                      Mumbai
A                      3                                 NA                     Bangalore       
B                      NA                            1                      Delhi       
A                      1                                 NA                     Delhi

Answer 1

Here you go...
<pre style="font-family: Andale Mono, Lucida Console, Monaco, fixed, monospace; color: #000000; background-color: #eee;font-size: 12px;border: 1px dashed #999999;line-height: 14px;padding: 5px; overflow: auto; width: 100%"><code>
SQL&gt; DROP TABLE A;
Table dropped.
SQL&gt; CREATE TABLE A ( ID INTEGER, VALUE VARCHAR2(20));
Table created.
SQL&gt; INSERT INTO A VALUES(1,'Delhi');
1 row created.
SQL&gt; INSERT INTO A VALUES(2,'Mumbai');
1 row created.
SQL&gt; INSERT INTO A VALUES(3,'Bangalore');
1 row created.
SQL&gt; DROP TABLE B;
Table dropped.
SQL&gt; CREATE TABLE B(TYPE CHAR(1), TYPE_A_ID CHAR(2), TYPE_B_ID CHAR(2));
Table created.
SQL&gt; INSERT INTO B VALUES ('A','1','NA');
1 row created.
SQL&gt; INSERT INTO B VALUES ('A','1','NA');
1 row created.
SQL&gt; INSERT INTO B VALUES ('B','NA','2');
1 row created.
SQL&gt; INSERT INTO B VALUES ('A','3','NA');
1 row created.
SQL&gt; INSERT INTO B VALUES ('B','NA','1');
1 row created.
SQL&gt; INSERT INTO B VALUES ('A','1','NA');
1 row created.
SQL&gt; COMMIT;
Commit complete.
SQL&gt;
SQL&gt; SELECT TYPE, TYPE_A_ID, TYPE_B_ID, VALUE
2 FROM A, (SELECT TYPE, TYPE_A_ID, TYPE_B_ID, DECODE(TYPE_A_ID,'NA',TYPE_B_ID,TYPE_A_ID) ID FROM B) B
3 WHERE A.ID = B.ID
4 /
T TY TY VALUE
A 1 NA Delhi
A 1 NA Delhi
B NA 1 Delhi
A 1 NA Delhi
B NA 2 Mumbai
A 3 NA Bangalore
6 rows selected.
</code></pre>
Karthick
http://www.karthickarp.blogspot.com/