user2210819 user2210819 - 1 month ago 13
MySQL Question

mysql transform fields to column

I have the following tables


table 1 table 2
id q_id content id w_id q_id c_id ranking
---------------------- ------------------------------------------------
95 2046 1=E 123 22404 2046 100 1

96 2046 2=G 124 22404 2046 101 2

97 2046 3=N 125 22404 2046 102 2

98 2046 4=B 126 22404 2046 103 2

99 2046 5=V 127 22404 2046 104 3

100 2046 A1 128 22404 2046 105 3

101 2046 A2

102 2046 A3

103 2046 A4

104 2046 A5

105 2046 A6


I need to transfrom the table row to column

The original Result:

 
c_id content E G N B V
----------------------------------------------
100 A1 1 0 0 0 0

101 A2 0 1 0 0 0

102 A3 0 1 0 0 0

103 A4 0 1 0 0 0

104 A5 0 0 1 0 0

105 A6 0 0 1 0 0



The code of Result 1 :

(SELECT c.id, c.content, a.E, a.G, a.N, a.B, a.V FROM table_1 t
INNER JOIN
(SELECT t1.id,
Count(IF(t2.ranking=1,1,0)) AS E,
Count(IF(t2.ranking=2,1,0)) AS G,
Count(IF(t2.ranking=3,1,0)) AS N,
Count(IF(t2.ranking=4,1,0))AS B,
Count(IF(t2.ranking=5,1,0)) AS V
FROM table_1 t1, table_2 t2
WHERE t1.question_id = 2046 AND t2.question_id = 2046 AND t2.choice_id = t1.id
AND t2.ranking >= 0 AND t2.w_id IN (22404)
GROUP BY t1.id) a ON a.id = t1.id);


To New Result:


content A1 A2 A3 A4 A5 A6
-----------------------------------------------
1=E 1 0 0 0 0 0

2=G 0 1 1 1 0 0

3=N 0 0 0 0 1 1

4=B 0 0 0 0 0 0

5=V 0 0 0 0 0 0



I am using MySql and I can't use pivot. Also, I think I will not know the no. of "A" in table 1 which means it may up to "A30". Therefore it should be dynamic.....
Can anyone give me advice for Result 2?




@bluefeet I think I need to add two more condition in where caluse since the left join may joined large amount of data in table_1. So it can't show the result.

select c.content,
sum(case when t1.content = 'A1' then 1 else 0 end) A1,
sum(case when t1.content = 'A2' then 1 else 0 end) A2,
sum(case when t1.content = 'A3' then 1 else 0 end) A3,
sum(case when t1.content = 'A4' then 1 else 0 end) A4,
sum(case when t1.content = 'A5' then 1 else 0 end) A5
from table_1 c
left join table_2 t2
on left(c.content, 1) = t2.ranking
left join table_1 t1
on t2.c_id = t1.id
where locate('=', c.content) > 0 and c.id IN (95,96,97,98,99) and w_id = 22404
group by c.content;


The result would be like this

| CONTENT | A1 | A2 | A3 | A4 | A5 | A6 |
-----------------------------------------
| 1=E | 1 | 0 | 0 | 0 | 0 | 0 |
| 2=G | 0 | 1 | 1 | 1 | 0 | 0 |
| 3=N | 0 | 0 | 0 | 0 | 1 | 1 |


two rows are missing (4=B , 5=V).

How can I solve it?

Answer

The following query should give you the result, however it makes a few assumptions:

  • The final content column will always have an equal sign = present. This is being used to locate the rows that are in the content.
  • The content column values with the = sign have the associated rank as the first character. This character is used to join the rows to the ranking in table_2

If you have a known number of values, then you can use the following:

select c.content,
  sum(case when t1.content = 'A1' then 1 else 0 end) A1,
  sum(case when t1.content = 'A2' then 1 else 0 end) A2,
  sum(case when t1.content = 'A3' then 1 else 0 end) A3,
  sum(case when t1.content = 'A4' then 1 else 0 end) A4,
  sum(case when t1.content = 'A5' then 1 else 0 end) A5
from table_1 c
left join table_2 t2
  on left(c.content, 1) = t2.ranking
left join table_1 t1
  on t2.c_id = t1.id
where locate('=', c.content) > 0
group by  c.content;

See SQL Fiddle with Demo.

If you are going to have an unknown number of A values, then you can use a prepared statement to generate dynamic SQL:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'sum(CASE WHEN t1.content = ''',
      content,
      ''' THEN 1 else 0 END) AS `',
      content, '`'
    )
  ) INTO @sql
FROM Table_1
where locate('=', content)= 0;

SET @sql 
  = CONCAT('SELECT c.content, ', @sql, ' 
            from table_1 c
            left join table_2 t2
              on left(c.content, 1) = t2.ranking
            left join table_1 t1
              on t2.c_id = t1.id
            where locate(''='', c.content) > 0
            group by  c.content;');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

See SQL Fiddle with Demo. Both give the result:

| CONTENT | A1 | A2 | A3 | A4 | A5 | A6 |
-----------------------------------------
|     1=E |  1 |  0 |  0 |  0 |  0 |  0 |
|     2=G |  0 |  1 |  1 |  1 |  0 |  0 |
|     3=N |  0 |  0 |  0 |  0 |  1 |  1 |
|     4=B |  0 |  0 |  0 |  0 |  0 |  0 |
|     5=V |  0 |  0 |  0 |  0 |  0 |  0 |
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