How Do Efficiently I Convert Dynamic Rows to Column in MySQL - mysql

Question

I'm looking for an efficient way to convert rows to columns in the SQL server, I heard that PIVOT is not very fast, and I need to deal with a lot of records.
I tried following on this Efficiently convert rows to columns in sql server but still not solved with my below example
This is my example: (updated)
-----------------------------------------------
| Id | Value | ColumnName | Submission_Id |
-----------------------------------------------
| 1 | John | FirstName | 1 |
| 2 | 2.4 | Amount | 1 |
| 3 | ZH1E4A | PostalCode | 1 |
| 4 | Fork | LastName | 1 |
| 5 | 857685 | AccountNumber | 1 |
| 6 | Donny | FirstName | 2 |
| 7 | 2.7 | Amount | 2 |
| 8 | ZH1E4C | PostalCode | 2 |
| 9 | Yen | LastName | 2 |
| 10 | 857686 | AccountNumber | 2 |
-----------------------------------------------
This is my expected result:
---------------------------------------------------------------------
| FirstName |Amount| PostalCode | LastName | AccountNumber |
---------------------------------------------------------------------
| John | 2.4 | ZH1E4A | Fork | 857685 |
| Donny | 2.7 | ZH1E4C | Yen | 857686 |
---------------------------------------------------------------------
How can I build the result?

Answer 1

You need to group them by their associative key, which you informed:
SELECT
MAX(CASE ColumnName WHEN 'FirstName' THEN Value END) AS FirstName,
MAX(CASE ColumnName WHEN 'Amount' THEN Value END) AS Amount,
MAX(CASE ColumnName WHEN 'PostalCode' THEN Value END) AS PostalCode,
MAX(CASE ColumnName WHEN 'LastName' THEN Value END) AS LastName,
MAX(CASE ColumnName WHEN 'AccountNumber' THEN Value END) AS AccountNumber
FROM table
GROUP BY submission_id
;
GROUP BY enforces that there is single row for each unique submission_id, MAX selects the most descendant value of the expression for that particular group key (it is assumed to be singular so aggregate type should not matter), and finally CASE is filtering the Value by ColumnName.

Answer 2

WITH
indata(Id,Value,ColumnName) AS (
SELECT 1,'John' ,'FirstName'
UNION ALL SELECT 2,'2.4' ,'Amount'
UNION ALL SELECT 3,'ZH1E4A' ,'PostalCode'
UNION ALL SELECT 4,'Fork' ,'LastName'
UNION ALL SELECT 5,'857685' ,'AccountNumber'
UNION ALL SELECT 6,'Donny' ,'FirstName'
UNION ALL SELECT 7,'2.7' ,'Amount'
UNION ALL SELECT 8,'ZH1E4C' ,'PostalCode'
UNION ALL SELECT 9,'Yen' ,'LastName'
UNION ALL SELECT 10,'857686','AccountNumber'
)
,
-- need to get a grouping column, one that
-- changes every time we encounter a 'FirstName
-- add a counter that is at 1 for FirstName
-- otherwise at 0, and build a running sum...
w_session_id AS (
SELECT
SUM(CASE ColumnName WHEN 'FirstName' THEN 1 END)
OVER(ORDER BY id) AS sessid
, *
FROM indata
)
-- now un-pivot manually
SELECT
sessid AS id
, MAX(CASE ColumnName WHEN 'FirstName' THEN value END) AS FirstName
, MAX(CASE ColumnName WHEN 'Amount' THEN value END) AS Amount
, MAX(CASE ColumnName WHEN 'PostalCode' THEN value END) AS PostalCode
, MAX(CASE ColumnName WHEN 'LastName' THEN value END) AS LastName
, MAX(CASE ColumnName WHEN 'AccountNumber' THEN value END) AS AccountNumber
FROM w_session_id
GROUP BY sessid;
-- out id | FirstName | Amount | PostalCode | LastName | AccountNumber
-- out ----+-----------+--------+------------+----------+---------------
-- out 1 | John | 2.4 | ZH1E4A | Fork | 857685
-- out 2 | Donny | 2.7 | ZH1E4C | Yen | 857686