mysql pivot/crosstab query - mysql

Question

Question 1: I have a table with the below structure and data:
app_id transaction_id mobile_no node_id customer_attribute entered_value
100 111 9999999999 1 Q1 2
100 111 9999999999 2 Q2 1
100 111 9999999999 3 Q3 4
100 111 9999999999 4 Q4 3
100 111 9999999999 5 Q5 2
100 222 8888888888 4 Q4 1
100 222 8888888888 3 Q3 2
100 222 8888888888 2 Q2 1
100 222 8888888888 1 Q1 3
100 222 8888888888 5 Q5 4
I want to display these records in the below format:
app_id | transaction_id | mobile | Q1 | Q2 | Q3 | Q4 | Q5 |
100 | 111 | 9999999999 | 2 | 1 | 4 | 3 | 2 |
100 | 222 | 8888888888 | 3 | 1 | 2 | 1 | 4 |
I know I need to use crosstab/pivot query to get this display. For this I tried it based on the limited knowledge that I have about it. Following is my query:
SELECT app_id, transaction_id, mobile_no,
(CASE node_id WHEN 1 THEN entered_value ELSE '' END) AS user_input1,
(CASE node_id WHEN 2 THEN entered_value ELSE '' END) AS user_input2,
(CASE node_id WHEN 3 THEN entered_value ELSE '' END) AS user_input3,
(CASE node_id WHEN 4 THEN entered_value ELSE '' END) AS user_input4,
(CASE node_id WHEN 5 THEN entered_value ELSE '' END) AS user_input5
FROM trn_user_log
GROUP BY app_id, transaction_id, mobile_no, node_id
And based on this query I got the below display:
app_id transaction_id mobile_no user_input1 user_input2 user_input3 user_input4 user_input5
100 111 9999999999 2
100 111 9999999999 1
100 111 9999999999 4
100 111 9999999999 3
100 111 9999999999 2
100 222 8888888888 3
100 222 8888888888 1
100 222 8888888888 2
100 222 8888888888 1
100 222 8888888888 4
Can anyone help me with the proper changes that I need to make to my query to get the records in one single row and not multiple rows as above.
Question 2: Also is there a way to get the value of a particular field as the NAME of the column. As you can see above I have user_input1, user_input2,... as the header. Instead of that I want to have the values in customer_attribute as the header of the columns.
For this I checked NAME_CONST(name,value) as below:
SELECT app_id, transaction_id, mobile_no,
NAME_CONST(customer_attribute, (CASE node_id WHEN 1 THEN entered_value ELSE '' END))
FROM trn_user_log
But it gives an error
Error Code : 1210 Incorrect arguments to NAME_CONST
Help required.

Answer 1

While #John's static answer works great, if you have an unknown number of columns that you want to transform, I would consider using prepared statements to get the results:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'GROUP_CONCAT((CASE node_id when ',
node_id,
' then entered_value else NULL END)) AS user_input',
node_id
)
) INTO #sql
FROM trn_user_log;
SET #sql = CONCAT('SELECT app_id, transaction_id, mobile_no, ', #sql, '
FROM trn_user_log
GROUP BY app_id, transaction_id, mobile_no');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
see SQL Fiddle with Demo
As far as your second, please clarify what you are trying to do it is not clear.

Answer 2

Add GROUP_CONCAT in your CASE clause
SELECT app_id, transaction_id, mobile_no,
GROUP_CONCAT((CASE node_id WHEN 1 THEN entered_value ELSE NULL END)) AS user_input1,
GROUP_CONCAT((CASE node_id WHEN 2 THEN entered_value ELSE NULL END)) AS user_input2,
GROUP_CONCAT((CASE node_id WHEN 3 THEN entered_value ELSE NULL END)) AS user_input3,
GROUP_CONCAT((CASE node_id WHEN 4 THEN entered_value ELSE NULL END)) AS user_input4,
GROUP_CONCAT((CASE node_id WHEN 5 THEN entered_value ELSE NULL END)) AS user_input5
FROM trn_user_log
GROUP BY app_id, transaction_id, mobile_no
SQLFiddle Demo

Answer 3

#DarkKnightFan, this was a very helpful question for a task I was working. I went ahead and modified the solution from #bluefin to solve your second question. The following code produces your originally requested format with the value of customer_attribute as the resulting column headings in the cross-tab.
The relevant change was to change:
' then entered_value else NULL END)) AS user_input',
node_id
To this:
' then entered_value else NULL END)) AS ''',
customer_attribute,''''
The full code:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'GROUP_CONCAT((CASE node_id when ',
node_id,
' then entered_value else NULL END)) AS ''',
customer_attribute,''''
)
) INTO #sql
FROM trn_user_log;
SET #sql = CONCAT('SELECT app_id, transaction_id, mobile_no, ', #sql, '
FROM trn_user_log
GROUP BY app_id, transaction_id, mobile_no');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Also, for other users browsing this issue, if you have a lot of values that you are trying to cross-tab, you may run into error because GROUP_CONCAT() has a default max length of 1024 characters. To increase put this at the start of your prepared statement:
SET SESSION group_concat_max_len = value; -- replace value with an int