Searchability.

using a linked table, you can do 
SELECT 
  * 
FROM 
  main_data 
WHERE 
  ROWID IN (
    SELECT link_id 
    FROM extra_data
    WHERE key1 = ?
    AND value1 LIKE ?
  )

[download]

Consider also:
do you want to put a storage method (JSON) inside a different storage method (SQL)?

In reply to Re^5: key value in text format by The_Dj
in thread key value in text format by pwagyi

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