Concatenate with string but exclude when null - sql

Question

Oracle v11
Exclude a string in a Concat when the value is NULL?
Work
Query:
Select
*
LastName || ',' || FirstName AS Last_First_Name
--I've tried using NVL & NVL2
--NVL(LastName || ',' || FirstName,'') AS Last_First_Name2
FROM TableA
TableA
LastName FirstName ID
Smith Ann 1
2
Output I'm getting
LastName FirstName ID LastName_FirstName
Smith Ann 1 Smith,Ann
2 ,
Expected Output:
LastName FirstName ID LastName_FirstName
Smith Ann 1 Smith,Ann
2

Answer 1

Use CASE
Select *,
CASE WHEN LastName IS NOT NULL AND FirstName IS NOT NULL
THEN LastName || ',' || FirstName AS Last_First_Name
END lastname_firstname
FROM TableA

Answer 2

Something like this... I added simulated inputs to test all four possibilities. However, note that if you may have last name but no first name, and also first name but no last name, the combined column will show just one name but you will not know if it is first or last. (Also, when a comma is added, I also add a space after the comma, as is usual; that can be controlled easily though.)
with
tablea ( lastname, firstname, id ) as (
select 'Smith', 'Ann' , 1 from dual
union all select null , null , 2 from dual
union all select 'Ang' , null , 3 from dual
union all select null , 'Murat', 4 from dual
)
-- End of simulated inputs (for testing only, not part of the solution).
-- SQL query begins BELOW THIS LINE. Use your actual table and column names.
select lastname, firstname, id,
lastname
|| case when lastname is not null and firstname is not null then ', ' end
|| firstname
as last_first
from tablea
;
LASTNAME FIRSTNAME ID LAST_FIRST
---------- ---------- ---------- ------------
Smith Ann 1 Smith, Ann
2
Ang 3 Ang
Murat 4 Murat

Answer 3

One way is to use a CASE statement to conditionally add the comma:
CASE WHEN LastName IS NULL
THEN LastName || ','
ELSE NULL
END
|| FirstName AS Last_First_Name

Answer 4

Oracle supports NULLIF. If both first and last name are null, the result will just be , which can be filtered.
SELECT
NULLIF(LastName ||','|| FirstName, ',') AS FullName
FROM table
Alternately, if you need to allow for when a single name is populated, you can use TRIM to remove leading/trailing commas.
SELECT
TRIM(',', LastName ||','|| FirstName) AS FullName
FROM table

Answer 5

By analogy, you can do with anything, including names.
Consider the example address:
select
SUBSTR(
(CASE WHEN city is null THEN '' ELSE ', ' || city END) ||
(CASE WHEN street is null THEN '' ELSE ', ' || street END) ||
(CASE WHEN house is null THEN '' ELSE ', ' || house END) ||
(CASE WHEN addition is null THEN '' ELSE ', ' || addition END)
, 3) as address
from departments;

Answer 6

You can concatenate any number of fields with delimiters using:
SELECT REGEXP_REPLACE(REGEXP_REPLACE(Col1 || ',' || Col2 || ',' || Col3, ',,*', ','), '^,|,$', '')
The inner REGEXP_REPLACE removes repeated delimiters occurring when you have interior NULL values.
The outer REGEXP_REPLACE removes the leading and trailing delimiters occurring if your list of values starts or ends with NULL.
If all values are NULL, returns NULL.