SQL Query - JOIN?

Question

Need your assistance on building a SQL query on the below requirement:

I have two tables as below:

TABLE A:

TASKNAME           HOSTNAME
---------------------------
12                 A1
34                 B
22                 C1
43                 D
65                 E1
93                 F

TABLE B:

HOST              NODE
----------------------
X                 ABC
X                 ABC
Y                 BV
B                 YTW
B                 IJK
D                 WWQ
D                 UWY
N                 J1
F                 ING
F                 UPI

I need to run the SQL query to compare these two TABLES and from table A it has to look for HOSTNAME value with HOST field in table B and the final outcome should be like below :

TASKNAME           HOSTNAME
---------------------------
12                 A1
34                 YTW
34                 IJK
22                 C1
43                 WWQ
43                 UWY
65                 E1
93                 ING
93                 UPI

Values B, D and F are common between those two tables.

Answer 1

You need a JOIN and NVL:

SELECT A.TASKNAME,
       NVL(B.NODE,A.HOSTNAME) AS HOSTNAME
FROM TableA A
LEFT JOIN TableB B
   ON A.HOSTNAME = B.HOST;