Oracle SQL - combine two columns - sql

Question

How can I combine two columns in Oracle SQL without using CASE?
I have to combine FirstName and LastName in the same row.
I have a table as below：
FirstName LastName
-----------------------
Ken Chan
John Ng
Joe Lam
The data type of these columns is VARCHAR2.
I try to apply the code as follow
SELECT
CONCAT(LastName, ‘,’, FirstName) AS FullName
FROM
LIST
ORDER BY
Place;
SELECT
LastName, ‘,’, FirstName AS FullName
FROM
LIST
ORDER BY
Place;
But both of them result in the the same error
ORA-00909: invalid number of arguments.
May I also ask how can I not adding the ‘,’ while there is missing LastName or FirstName?
Such as not adding ‘,’ when there is only having LastName Chan. The FullName only display as Chan but not ,Chan.
Thanks a lot for helping me.

Answer 1

Use Concatenation Operator that is ||. It concatenates character strings and results in another character string.
To make , comma optional in case if any of the LastName or firstName field is empty or null, use CASE statement.
Solution for your problem:
SELECT LastName || (CASE WHEN LastName IS NOT NULL AND FirstName IS NOT NULL THEN ',' END) || FirstName as FullName
FROM LIST
ORDER BY place;
Working Example: db<>fiddle Link
For more info on Concatenation Operator follow below link to official docs:
https://docs.oracle.com/cd/B19306_01/server.102/b14200/operators003.htm

Answer 2

Oracle's implementation of the concat() function only permits 2 parameters, and you have tried 3, that is why you got the error message.
It is simpler, in Oracle, to use the more traditional double pipe operator to form a concatenated string.
SELECT LastName || ‘,’ || FirstName as FullName
from LIST
order by Place;