Combining Data in Two Tables SQL

Question

I'm sure a very basic question, but I'm continue to be stuck:

Table A - image_number, camera_type, total_sales
Table B - image_number, keyword

Table A has one ROW for each image_number - example:

image_number="AXJ789, camera_type="Nikon", total_sales=678
image_number="JIJ123", camera_type="Canon", total_sales=999
image_number="KNI908", camera_type="Sony", total_sales=565

Table B has many ROWs for each image_number - example:

image_number="AXJ789", keyword = "rain"
image_number="AXJ789", keyword = "mountain"
image_number="AXJ789", keyword = "grass"
image_number="AXJ789", keyword = "cloud"

What I'm trying to do is JOIN the two tables so that I can generate the following output:

image_number="AXJ789", camera_type=678, camera_type="Nikon", keyword(1) = "rain", keyword(2) = "mountain", keyword(3) = "grass", keyword(4) = "cloud"

In other words, I want to have all items in each ROW in table A + all the items from table B. For each image_number in Table A, there could be no "keywords" in Table B or 50 keywords - depends on the image.

When I do an INNER JOIN, of course I can get one "keyword" from table B, but I can't figure out how to get all of them.

Answer 1

You can concatenate the keywords together:

select a.*,
       (select group_concat(b.keyword)
        from b
        where b.image_number = a. image_number
       ) as keywords
from a;

This creates a comma-delimited list of the keywords. This is much simpler (in MySQL) than trying to put them in separate columns. In fact, if you wanted separate columns, I might suggest parsing this result:

select a.*,  -- or whatever columns you want
       substring_index(keywords, ',' 1) as keyword1,
       substring_index(substring_index(keywords, ',' 2), ',', -1) as keyword2,
       substring_index(substring_index(keywords, ',' 3), ',', -1) as keyword3,
       substring_index(substring_index(keywords, ',' 4), ',', -1) as keyword4
from a left join 
     (select b.image_number, group_concat(b.keyword) as keywords
      from b
      group by b.image_number
     ) b
     on b.image_number = a. image_number;

Answer 2

You can generate a comma-separated list of keywords for each image using GROUP_CONCAT and JOIN (but use a LEFT JOIN if an image may have no keywords).

SELECT a.*, GROUP_CONCAT(b.keyword) AS keyword_list
FROM a
JOIN b on b.image_number = a.image_number
GROUP BY a.image_number

Output for your sample data:

image_number    camera_type     total_sales     keyword_list
AXJ789          Nikon           678             rain,mountain,grass,cloud

Demo on dbfiddle

You can then parse this into an array in your application, for example in PHP (if you have read the row into $row ):

$keywords = explode(',', $row['keyword_list']);
print_r($keywords);

Output:

Array
(
    [0] => rain
    [1] => mountain
    [2] => grass
    [3] => cloud
)