how to insert multiple columns in a single column of another table in sql

Question

I have the following table:

Then I want to get the following:

I want to achieve this in postgres. What should I do?

Answer 1

Tabular data can be easily unpivoted with the help of JSON functions.

The query below will work, assuming tablename is replaced by your table name, and primary_key is the name of the pivot column. The other columns don't have to be specified, they're obtained automatically by json_each_text applied to row_to_json applied to all rows.

SELECT primary_key, key, value
 FROM (select row_to_json(t.*) AS line, primary_key
     FROM tablename AS t) AS r
   JOIN LATERAL json_each_text(r.line)
     ON (key <> 'primary_key')