SQL IS NOT NULL for CASE WHEN

Question

My current database is in the follow format,

| question_id |Tag  | Question  |
|      -      |-   --|--        -|
|1            | EN   | DOG       |
|1            | DE   | HUND      |

and i'm trying to create a result such as;

| question_id |English  | German    |
|      -      |-      --|--        -|
|1            | DOG     | HUND       |

I currently have a case when set up;

select  question_id
  , CASE WHEN tag = 'en'
               THEN text
          END AS "ENGLISH",
   CASE WHEN tag = 'de'
              THEN text
          END AS "GERMAN"
from table

The problem is because I have two case when(s), it end up returning duplicate rows

  | question_id |English  | German    |
|      -      |-      --|--        -|
|1            | NULL     | HUND       |
|1            | DOG     | NULL       |

My attempt to fix this, was to add a WHERE "ENGLISH" IS NOT NULL to the end of the statement to delete these rows, but SQL doesn't seem to recognise that case when columns are real columns.

Answer 1

You could use aggregation:

SELECT question_id,
       max(text) FILTER (WHERE tag = 'en') AS english,
       max(text) FILTER (WHERE tag = 'de') AS german
FROM atable
GROUP BY question_id;

Answer 2

you could use aggregation with case when as well

select  question_id
  , max(CASE WHEN tag = 'en'
               THEN text
          END )AS ENGLISH,
   max (CASE WHEN tag = 'de'
              THEN text
          END) AS GERMAN
from table group by question_id

Answer 3

CREATE TABLE test_table(question_id NUMBER,
tag VARCHAR2(10),
question VARCHAR2(10));

INSERT INTO test_table VALUES(1,'EN','DOG');
INSERT INTO test_table VALUES(1,'DE','HUND');

COMMIT;


SELECT QUESTION_ID,
MAX(CASE WHEN TAG='EN' THEN QUESTION END) AS ENGLISH,
MAX(CASE WHEN TAG='DE' THEN QUESTION END) AS GERMAN
FROM test_table
GROUP BY QUESTION_ID;

I tried the expected result for the above sample set of data.