Print message when no data is found - sql

Question

Need a query to get the Employee name, total fuel used by each employee.
If fuel is not used by an employee then the second column should have a
text “No fuel used”.
These are the following two tables:
Table1: EmployeeID, FirstName
1 Vikas
2 nikita
3 Ashish
4 Nikhil
5 anish
Table2: ID, Fuel
1 10
2 9
3 8
4 6
5 12
6 11
7 10
8 9
9 8
10 10
11 9
12 12
13 7
14 15
where The column table2.ID is a foreign key to table1.EmployeeID.
This is code which I have written, Which is most probably wrong.
select ID, FirstName, sum(table2.Fuel) sum_fuel
from table2,table1
where EmployeeID=ID IN (
select ID, coalesce(ID, 'No-fuel used') as ID
from table1 t1
left join table2 t2 on t2.ID = t1.EmployeeID
)
group by fuel
order by ID DESC;
As you can see from two tables that employee with from 1 to 5 of table1 are in table2. So for these employee I need to show total fuel used by every individual. And for employee with ID from 6 to 14 are not available in table1 so for these employee “No fuel used” message should be printed.

Answer 1

You can use a left join. This way, whenever the Id values for tables don't match you'll get null values for sum(fuel) value, and will assign the string 'No fuel used'for sum_fuel column by using nvl() function:
with table1( EmployeeID, FirstName ) as
(
select 1,'Vikas' from dual union all
select 2,'nikita' from dual union all
select 3,'Ashish' from dual union all
select 4,'Nikhil' from dual union all
select 5,'anish' from dual union all
select 15,'pratteek' from dual
), table2( ID, Fuel ) as
(
select 1, 10 from dual union all
select 2, 9 from dual union all
select 3, 8 from dual union all
select 4, 6 from dual union all
select 5, 12 from dual union all
select 6, 11 from dual union all
select 7, 10 from dual union all
select 8, 9 from dual union all
select 9, 8 from dual union all
select 10, 10 from dual union all
select 11, 9 from dual union all
select 12, 12 from dual union all
select 13, 7 from dual union all
select 14, 15 from dual
)
select EmployeeID, FirstName, nvl(to_char(sum(t2.Fuel)),'No fuel used') as sum_fuel
from table1 t1
left join table2 t2
on t1.EmployeeID = t2.ID
group by EmployeeID, FirstName
order by EmployeeID desc;
EMPLOYEEID FIRSTNAME SUM_FUEL
---------- --------- ------------
15 pratteek No fuel used
5 anish 12
4 Nikhil 6
3 Ashish 8
2 nikita 9
1 Vikas 10
Demo

Answer 2

This may work---
SELECT ID
, FirstName
, CASE
WHEN SUM(f.Fuel) > 0 THEN CAST(SUM(f.Fuel) AS NVARCHAR(25))
ELSE 'No fuel used'
END sum_fuel
FROM #emp e
LEFT JOIN #fuel f ON e.EmployeeID = f.id
GROUP BY ID,FirstName
ORDER BY ID DESC