Question

I have data in a mysql table in long / tall format (described below) and want to convert it to wide format. Can I do this using just sql?

Easiest to explain with an example. Suppose you have information on (country, key, value) for M countries, N keys (e.g. keys can be income, political leader, area, continent, etc.)

Long format has 3 columns: country, key, value
  - M*N rows.
  e.g. 
  'USA', 'President', 'Obama'
   ...
  'USA', 'Currency', 'Dollar'

Wide format has N=16 columns: county, key1, ..., keyN
  - M rows
example: 
   country, President, ... , Currency
   'USA', 'Obama', ... , 'Dollar'

Is there a way in SQL to create a new table with the data in the wide format?

select distinct key from table;

// this will get me all the keys.

1) How do I then create the table using these key elements?

2) How do I then fill in the table values?

I’m pretty sure I can do this with any scripting language (I like python), but wanted to know if there is an easy way to do this in mysql. Many statistical packages like R and STATA have this command built in because it is often used.

======

To be more clear, here is the desired input output for a simple case:

Input:

country    attrName    attrValue     key  (these are column names)
US         President   Obama         2
US         Currency    Dollar        3
China      President   Hu            4
China      Currency    Yuan          5

Output

country    President    Currency    newPkey
US         Obama        Dollar      1
China      Hu           Yuan        2

Answer 1

Cross-tabs or pivot tables is the answer. From there you can SELECT FROM … INSERT INTO … or create a VIEW from the single SELECT.

Something like:

SELECT country, 
       MAX( IF( key='President', value, NULL ) ) AS President,
       MAX( IF( key='Currency', value, NULL ) ) AS Currency,
       ...

FROM table 
GROUP BY country;