Concatenate SQL table rows with conditions in single text - sql

Question

I have a SQL table like this
col1 col2 col3
1 0 1
1 1 1
0 1 1
1 0 0
0 0 0
I am expecting output as like this
col1 col2 col3 NewCol
1 0 1 SL,PL
1 1 1 SL,EL,PL
0 1 1 EL,PL
1 0 0 SL
0 0 0 NULL
The condition for this is if col1>0 then SL else ' ', if col2>0 EL else ' ', if col3>0 PL else ' '
I tried to use Concatenate many rows into a single text string? but didn't able to achieve the desired result properly
I have tried It is working fine with a message
Invalid length parameter passed to the LEFT or SUBSTRING function.
WITH CTE AS (
SELECT col1, col2, col3,
CASE WHEN col1 > 0 THEN 'SL,' ELSE '' END +
CASE WHEN col2 > 0 THEN 'EL,' ELSE '' END +
CASE WHEN col3 > 0 THEN 'PL,' ELSE '' END AS NewCol
FROM Employee
)
SELECT col1, col2, col3,
substring(NewCol, 1, len(NewCol) - 1) AS NewCol
FROM CTE
But again my last condition is not matching if all columns is 0 then I have to show NULL as per desired output.
Find the attach fiddle http://sqlfiddle.com/#!6/2bd6a/1

Answer 1

The issue with your code example is that when all columns are 0 then the length is 0 and the substring function will throw an error.
Use nullif to fix it: substring(NewCol, 1, len(nullif(NewCol,'')) - 1) AS NewCol

Answer 2

You could also change to appending the delimiter on the front and use STUFF.
STUFF('',1,1,'') will return NULL rather than an error.
WITH
Employee(col1, col2, col3) AS (
SELECT 1,1,1 UNION ALL
SELECT 0,0,0
),
CTE AS (
SELECT col1, col2, col3,
CASE WHEN col1 > 0 THEN ',SL' ELSE '' END +
CASE WHEN col2 > 0 THEN ',EL' ELSE '' END +
CASE WHEN col3 > 0 THEN ',PL' ELSE '' END AS NewCol
FROM Employee
)
SELECT col1,
col2,
col3,
STUFF(NewCol, 1, 1, '')
FROM CTE
Returns
+------+------+------+------------------+
| col1 | col2 | col3 | (No column name) |
+------+------+------+------------------+
| 1 | 1 | 1 | SL,EL,PL |
| 0 | 0 | 0 | NULL |
+------+------+------+------------------+

Answer 3

You have to check with NULLIF to do this trick
Two ways
SELECT col1, col2, col3,
nullif(CASE WHEN col1 = 1 THEN 'SL,' ELSE '' END +
CASE WHEN col2 = 1 THEN 'EL,' ELSE '' END +
CASE WHEN col3 = 1 THEN 'PL,' ELSE '' END,'') AS NewCol
FROM Employee
OR
SELECT
col1,
col2,
col3,
substring(nullif(NewCol,''), 1, len(NewCol) - 1) AS NewCol
FROM
CTE