How Can I Transpose User-Defined Field Values in SQL?

SQL Transposing Techniques for User-Defined Field Values

In SQL, you may encounter situations where you need to transpose data stored in rows to form columns. One such example is when you have a table like the one described below:

================================================
| Id | UserId | FieldName     | FieldValue     |
=====+========+===============+================|
| 1  | 100    | Username      | John Doe       |
|----+--------+---------------+----------------|
| 2  | 100    | Password      | pass123!       |
|----+--------+---------------+----------------|
| 3  | 102    | Username      | Jane           |
|----+--------+---------------+----------------|
| 4  | 102    | Password      | $ecret         |
|----+--------+---------------+----------------|
| 5  | 102    | Email Address | [email protected] |
------------------------------------------------

To transpose this data into a format where the FieldNames become column headers and the FieldValues form the corresponding row data, you can leverage the following SQL query:

  SELECT t.userid
         MAX(CASE WHEN t.fieldname = 'Username' THEN t.fieldvalue ELSE NULL END) AS Username,
         MAX(CASE WHEN t.fieldname = 'Password' THEN t.fieldvalue ELSE NULL END) AS Password,
         MAX(CASE WHEN t.fieldname = 'Email Address' THEN t.fieldvalue ELSE NULL END) AS Email
    FROM TABLE t
GROUP BY t.userid

However, for this approach to work effectively, you would need to define CASE statements for each expected FieldName value. To enhance flexibility, consider implementing MySQL's Prepared Statement (dynamic SQL) syntax for dynamically generating these CASE statements.

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