MySQL Select Data From two tables and generate column name dynamically - mysql

Question

1: Product info (corewp_product) 2: Product Metadata (corewp_productmeta)
I want to select (assume the user is searching) by price, color, size e.t.c metadata depending on the search parameter and metadata available.
Eg. search might be
where (color=red and price between 100 and 500)
Since metadata is dynamically added I don't want to create a new column for each metadata. Some of the products are in group (eg. Sneaker might be in red,blue with various prices)
My Tables are like this:
corewp_product
id
idname
title
category
price
type
meta
1
A1
Sneakers
2
0
grouped
0
2
A2
Branded Shirts for sale
1
0
grouped
0
3
A3
Long Sleeve Shirts
1
0
grouped
0
corewp_productmeta
id
postid_field
group_id
meta_name
meta_value
1
A1
G1
color
red
2
A1
G1
size
EU40
3
A1
G1
price
28
4
A1
G2
color
black
5
A1
G2
size
EU41
6
A1
G2
price
30
7
A1
G3
color
red
8
A1
G3
size
E40
9
A1
G3
price
50
10
A2
G1
color
any
11
A2
G1
size
L
12
A2
G1
price
60
13
A3
G1
color
red
14
A3
G1
price
30
Problem:
Selecting products with color = red and price between 0 and 50 or with other metadata.
Approach 1- using join:
I have tried to do it this way
SELECT corewp_product.id, corewp_product.idname, corewp_product.title, P.amount, C.color FROM corewp_product JOIN ( SELECT `postid_field` as priceId, `meta_value` as amount, `group_id` as ggroup FROM `corewp_productmeta` WHERE (`meta_name` = 'price' AND `meta_value` BETWEEN 10 AND 50)) AS P JOIN (SELECT `postid_field` as colorId, `meta_value` as color, `group_id` as ggroup FROM `corewp_productmeta` WHERE (`meta_name` = 'color' AND `meta_value` = 'red') GROUP BY `group_id`,`postid_field`) AS C ON p.ggroup = C.ggroup WHERE corewp_product.idname = P.priceId AND corewp_product.idname = C.colorId
But the problem with the code above is what happen when a new meta data is added e.g: brand name
id
postid_field
group_id
meta_name
meta_value
15
A1
G1
brand
nike
and the new search has to include brand name color = red and brand = nike and price between 0 and 50, I will have to alter the query above which is something am looking to avoid.
Approach 2- using view:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'MAX(IF(pm.meta_name = ''',
meta_name,
''', pm.meta_value, NULL)) AS ',
meta_name
)
) INTO #sql
FROM corewp_productmeta;
SET #sql = CONCAT('SELECT p.idname , p.title, ', #sql, ' FROM corewp_product p LEFT JOIN corewp_productmeta AS pm ON p.idname = pm.postid_field GROUP BY pm.group_id,p.idname,p.title');
SET #qrys = CONCAT('CREATE OR REPLACE VIEW meta_view AS ',#sql);
PREPARE stmt FROM #qrys;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
The approach works as expected but now I have to get all the data from the view table which also I want to avoid now an issue comes when a new meta data is added e.g. brand same issue repeat.
It will be great if I could be able to query like select... where brand=xx and color=aa then results would come with column brand and name if brand doesn't exist then brand column returned as null or result not found same with other dynamic values passed in a query
Is there any way you can help me guys? I will appriciate.
N.B: this query will also include pagination limit (0,10) once full system is deployed.
SQL FORMAT
CREATE TABLE `corewp_product` (
`id` int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
`idname` varchar(20) NOT NULL,
`title` varchar(60) NOT NULL,
`category` int(11) NOT NULL,
`price` double(20,2) NOT NULL,
`type` varchar(20) NOT NULL,
`meta` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `corewp_product` (`id`, `idname`, `title`, `category`, `price`, `type`, `meta`) VALUES
(1, 'A1', 'Sneakers', 2, 0.00, 'grouped', 0),
(2, 'A2', 'Branded Shirts for sale', 1, 0.00, 'grouped', 0),
(3, 'A3', 'Long Sleeve Shirts', 1, 0.00, 'grouped', 0);
CREATE TABLE `corewp_productmeta` (
`id` int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
`postid_field` varchar(5) NOT NULL,
`group_id` varchar(5) NOT NULL,
`meta_name` varchar(50) NOT NULL,
`meta_value` varchar(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `corewp_productmeta` (`id`, `postid_field`, `group_id`, `meta_name`, `meta_value`) VALUES
(1, 'A1', 'G1', 'color', 'red'),
(2, 'A1', 'G1', 'size', 'EU40'),
(3, 'A1', 'G1', 'price', '28'),
(4, 'A1', 'G2', 'size', 'EU41'),
(5, 'A1', 'G2', 'color', 'black'),
(6, 'A1', 'G2', 'price', '30'),
(7, 'A1', 'G3', 'color', 'red'),
(8, 'A1', 'G3', 'size', 'E40'),
(9, 'A1', 'G3', 'price', '50'),
(10, 'A2', 'G1', 'color', 'any'),
(11, 'A2', 'G1', 'size', 'L'),
(12, 'A2', 'G1', 'price', '60'),
(13, 'A3', 'G1', 'color', 'red'),
(14, 'A3', 'G1', 'price', '30');

Answer 1

WITH vars AS (
SELECT postid_field,title,
GROUP_CONCAT(IF(meta_name='color', meta_value, NULL) SEPARATOR '') color,
GROUP_CONCAT(IF(meta_name='size', meta_value, NULL) SEPARATOR '') size,
GROUP_CONCAT(IF(meta_name='price', meta_value, NULL) SEPARATOR '') price
FROM corewp_productmeta,corewp_product
WHERE postid_field = idname
GROUP BY group_id,postid_field,title
)
select * from vars
where price > 29 AND price < 59
Query Demo
The query uses the WITH clause to create a sub-query that joins the two tables and assigns the resulting table to a variable eg: vars.
After that, you can query from the variable like any normal table and apply your filters in the where clause and you can filter using the extended columns. eg: where price > 29 AND price < 59
Check the Query Demo on the link above.

Answer 2

where (color=red and price between 100 and 500)
SELECT pr.*
FROM corewp_product pr
JOIN corewp_productmeta pm ON pr.idname = pm.postid_field
WHERE (pm.meta_name = 'color' AND meta_value = 'red')
OR (pm.meta_name = 'price' AND meta_value + 0 BETWEEN 100 AND 500)
GROUP BY pr.id
HAVING COUNT(*) = 2;
DEMO
Some explanations.
We select the metadata rows which matches any of the criteria. Then we group by the product and count the amount of matched meta values for it. Finally we return only those products which have the matched amount equal to total one.
This query does not need in dynamic SQL. You must only put correct values into the conditions.
Pay attention to this: meta_value + 0 BETWEEN 100 AND 500. The addition + 0 performs implicit data casting to numeric (of course we can use explicit CAST(meta_value AS UNSIGNED)). This allows make numeric comparing context. Without this addition the comparing context will be string, and we may obtain incorrect output (for example, for "price between 50 and 100").