Nrthugu

I wanted to read a table which has values which will be the column names of the sql query result.
For example, I have table1 as ..

id    col1     col2

----------------------

0      name    ax

0      name2   bx

0      name3   cx

1      name    dx

1      name2   ex

1      name2   fx

If u see for id = 0, name has value of ax and name 2 - bx and name3 = cx
instead of this being rows it would be easier to show columns as id, name, name2, name3
Now I want the result of the query to look like this

id   name    name2     name3

0    ax      bx         cx

1    dx      ex         fx

Can someone help me in achieving this ?

This is done with a pivot table. Grouping by id, you issue CASE statements for each value you want to capture in a column and use something like a MAX() aggregate to eliminate the nulls and collapse down to one row.

SELECT

  id,

  /* if col1 matches the name string of this CASE, return col2, otherwise return NULL */

  /* Then, the outer MAX() aggregate will eliminate all NULLs and collapse it down to one row per id */

  MAX(CASE WHEN (col1 = 'name') THEN col2 ELSE NULL END) AS name,

  MAX(CASE WHEN (col1 = 'name2') THEN col2 ELSE NULL END) AS name2,

  MAX(CASE WHEN (col1 = 'name3') THEN col2 ELSE NULL END) AS name3

FROM

  yourtable

GROUP BY id

ORDER BY id

Here's a working sample

Note: This only works as is for a finite and known number of possible values for col1. If the number of possible values is unknown, you need to build the SQL statement dynamically in a loop.

What you are attempting to do is a PIVOT MySQL does not have a PIVOT function so you can replicate this using a CASE and an aggregate function.

If you have a known number of columns, then you can use a static version and hard-code the values. Similar to this (See SQL Fiddle with demo):

select id,

  max(case when col1='name' then col2 end) name,

  max(case when col1='name2' then col2 end) name2,

  max(case when col1='name3' then col2 end) name3

from yourtable

group by id

But if you have an unknown number of columns, then you can use a prepared statement and create this dynamically:

SET @sql = NULL;

SELECT

  GROUP_CONCAT(DISTINCT

    CONCAT(

      'max(case when col1 = ''',

      col1,

      ''' then col2 end) AS ',

      col1

    )

  ) INTO @sql

FROM yourtable;



SET @sql = CONCAT('SELECT id, ', @sql, ' 

                  FROM yourtable 

                  GROUP BY id');



PREPARE stmt FROM @sql;

EXECUTE stmt;

DEALLOCATE PREPARE stmt;

See SQL Fiddle with Demo

select id,

    max(if(tablename.columnname = 'name',tablename.columnname,null)) as namealise,

    max(if(tablename.columnname = 'name1',tablename.columnname,null)) as namealise1 

from table1, table2 

where table1.id = table2.id 

group by table1.id 

order by table1.id