How to show multiple values of a single field in a single row in a single query?

Question

Table 1:Domain Link Result
======================================================================
||Column1(words)     ||Column2(links)    ||Column3(frequency)       ||
======================================================================
    1                   1                   Any Number
    2                   1                   Any Number
    3                   1                   Any Number
    4                   1                   Any Number
    1                   2                   Any Number
    2                   2                   Any Number
    3                   2                   Any Number
    4                   2                   Any Number


Table 2:Sub Link Result
======================================================================
||Column1(words)     ||Column2(sublinks)    ||Column3(frequency)    ||
======================================================================
    1                   a                   Any Number
    2                   b                   Any Number
    3                   c                   Any Number
    4                   d                   Any Number
    1                   e                   Any Number
    2                   f                   Any Number
    3                   g                   Any Number
    4                   h                   Any Number

And so on.

In the above scenario user entered 4 words and 2 domain links. Now the frequency of 4 keywords is calculated on domain links as well sublinks and stored in separate tables as shown above. I want an aggregate result like below:

Table 3:Final Result
==================================================================================
||Column1(words)     ||Column2(Domain links)    ||Column3(Total frequency)      ||
==================================================================================
Row1:    1              1                    Total of frequency in both tables
                        2                    for word "1"   
----------------------------------------------------------------------------------
Row2:    2              1                    Total of frequency in both tables
                        2                    for word "2"   
----------------------------------------------------------------------------------
Row3:    3              1                    Total of frequency in both tables
                        2                    for word "3"   
----------------------------------------------------------------------------------
Row4:    4              1                    Total of frequency in both tables
                        2                    for word "4"   
----------------------------------------------------------------------------------

I tried the following query in MySQL:

SELECT t.`keyword`, t.`link` SUM( t.`frequency` ) AS total
FROM (

SELECT `frequency`
FROM `domain_link_result`
WHERE `keyword` = 'national'
UNION ALL
SELECT `frequency`
FROM `sub_link_result`
WHERE `keyword` = 'national'
)t GROUP BY `keyword`

But in Column 2 of the final result I get only first link instead of two links for row 1. How can I get both links or any number of links entered by user in a single row ?

Words and Links have VARCHAR as type and frequency has INT type.

Answer 1

If you want to collapse several rows into one and still be able to see the information, you have to use GROUP_CONCAT

http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

This outputs the collapsed values separated by commas, ie: a string. In your programming language you can split this string if you need individual values.

Your query would look somehow like this

SELECT keyword, GROUP_CONCAT(links), SUM(frequency)

FROM (subquery)

GROUP BY keyword

Which would output something like this:

==================================================================================
||Column1(words)     ||Column2(Domain links)    ||Column3(Total frequency)      ||
==================================================================================
Row1:    1              1,2                     sum of freq.
----------------------------------------------------------------------------------
Row2:    2              1,2                     sum of freq.
----------------------------------------------------------------------------------
Row3:    3              1,2                     sum of freq.
----------------------------------------------------------------------------------
Row4:    4              1,2                     sum of freq.

EDIT: Extra help for your query

Your query looks a little bit confusing to me. Try with a JOIN approach:

SELECT domain_link_results.word AS word,
       GROUP_CONCAT(domain_link_results.links) AS domain_links,
       domain_link_results.frequency + sub_link_results.frequency AS total_frequency

FROM domain_link_results

INNER JOIN sub_link_results
        ON domain_link_results.word = sub_link_results.word

WHERE domain_link_results.word = "national"

GROUP BY domain_link_results.word

On the other hand, it might be better to have all the links in the same table, and an extra field to determine if it's a domain link or a sublink. Without knowing more about your system it is hard to say.