从现有值在mysql视图中创建新列

Question

I am incredibly new at this so let me know if I can clarify. Essentially I am looking to create a new column in a mysql view based on values from a column in an existing table. I'm using phpGrid to output on the front end.

For instance - let's say I have existing column question_id :

    name | question_id | answer
----------------------------------
    Joe  | 1           | yes
    Joe  | 2           | no
    Ann  | 1           | maybe
    Ann  | 2           | kinda

and I have custom view my_view where I want the columns to be as such (not necessarily with question_id= in front, but whatever works):

    name  | question_id=1 | question_id=2
------------------------------------------
    Joe   | yes           | no
    Ann   | maybe         | kinda

Or something to that effect. How do I get the question_id values to become columns, and the answers in the right place?

Also, if name is from one table, and question_id is from another, how can I get the correctly associated values alongside each other in my_view ? name values often have duplicates, but they have individual entry ids.

Cheers and thanks!

EDIT: Create MySQL view using distinct values as columns is the right idea, but I get error #1064 about incorrect syntax.

Also, I'm not sure it solves the second problem of getting the data to align by unique entry ID. I tried to use this: 1052: Column 'id' in field list is ambiguous to fix the ambiguous issue but then I get error #1060 that there is a duplicate.

EDIT 2: Here is the code I use to try to get the columns from two separate tables, including the shared registration_id column present in both. I got the code from the post above regarding solving the ambiguous issue:

CREATE VIEW access AS
    SELECT fname,lname,email,city,state,country_id,phone,payment_status,event_id,wp_events_attendee.registration_id,wp_events_answer.registration_id,question_id,answer
    FROM wp_events_answer
    JOIN wp_events_attendee ON wp_events_attendee.registration_id = wp_events_answer.registration_id 

It gives me "#1060 - Duplicate column name 'registration_id'". Also not sure how to integrate that into the code seen at Create MySQL view using distinct values as columns . I tried to do a test:

  CREATE VIEW access AS
SELECT
    fname,lname,email,city,state,country_id,phone,payment_status,event_id,wp_events_attendee.registration_id,wp_events_answer.registration_id,question_id,answer,registration_id,
    MAX(IF(question_id = '1', status, NULL)) FIRST,
    MAX(IF(question_id = '11', status, NULL)) DOB,
FROM wp_events_answer, wp_events_attendee
JOIN wp_events_attendee ON wp_events_attendee.registration_id = wp_events_answer.registration_id 
GROUP BY registration_id;

But got "#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM wp_events_answer, wp_events_attendee GROUP BY registration_id' at line 6". Thanks!

Answer 1

I don't have much knowledge about sql views, but it seems there is a problem in your query when joining tables.

if you need to join 3 tables, follow the query below.

SELECT `table1`.`column1`,`table2`.`column2` 
FROM `table1` 
JOIN `mapping_table` 
JOIN `table2` 
ON `table1`.`table1_id`=`mapping_table`.`table1_foreign_key` 
AND `mapping_table`.`table2_foreign_key`=`table2`.`table2_id` 
GROUP BY `table1`.`group_column` 

Hope this will help you to create the view you want

Answer 2

Assuming you know the questions ids in advance this could be achieved with a bunch of UNIONS - http://sqlfiddle.com/#!9/00a0c/8

I'm afraid I'd need some sample data to answer the second part of your question.

UPDATE - I didn't realise that the additional rows were a problem. The following SQL fiddle addresses this issue.

http://sqlfiddle.com/#!9/0f8c7/2