How to query mysql to select and group by multiple values - mysql

Question

I'm trying to select and group by all the contentid values of the table below where the match criteria can be several different values.
the contentid values actually represent cars, so I need to select [and group by] all the contentis where the values are 'GMC' and the values are 'sedan' and the value is 'automatic.
i.e. I'm trying to select all the GMC sedans with an automatic transmission.
a query like this fails [obviously]:
select * from modx_site_tmplvar_contentvalues WHERE
`value` = 'gmc' and
`value` = 'tacoma'
group by contentid
I have no idea how to create a query like that. Any suggestions?

Answer 1

You need to "pivot" these data on "tmplvarid", but unfortunately for you MySQL doesn't have a PIVOT statement like other RDBMS. However, you can pivot it yourself by joining in the table multiple times for each variable you care about:
SELECT
contents.contentid,
transmission.value as transmission,
type.value as type,
make.value as make
FROM
(SELECT DISTINCT contentid FROM modx_site_tmplvar_contentvalues) AS contents
LEFT JOIN
modx_site_tmplvar_contentvalues AS transmission
ON contents.contentid = transmission.contentid
AND transmission.tmplvarid = 33 -- id for transmission
LEFT JOIN
modx_site_tmplvar_contentvalues AS make
ON contents.contentid = make.contentid
AND make.tmplvarid = 13 -- id for make
LEFT JOIN
modx_site_tmplvar_contentvalues AS type
ON contents.contentid = type.contentid
AND type.tmplvarid = 17 -- id for type
WHERE
type.value = 'sedan'
AND make.value = 'GMC'
AND transmission.value = 'automatic'
You can expand this with additional joins for other criteria such as year (id 15) or mileage (id 16).
If you need to use the value only, you could try:
SELECT DISTINCT
contents.contentid,
transmission.value as transmission,
type.value as type,
make.value as make
FROM
(SELECT DISTINCT contentid FROM modx_site_tmplvar_contentvalues) AS contents
INNER JOIN
modx_site_tmplvar_contentvalues AS transmission
ON contents.contentid = transmission.contentid
AND transmission.value = 'automatic'
INNER JOIN
modx_site_tmplvar_contentvalues AS make
ON contents.contentid = make.contentid
AND make.value = 'GMC'
INNER JOIN
modx_site_tmplvar_contentvalues AS type
ON contents.contentid = type.contentid
AND type.value = 'sedan'
In any case, make sure you have an index on the value column; these queries are going to get slow.

Answer 2

please try this:
SELECT *
FROM modx_site_tmplvar_contentvalues t1 INNER JOIN modx_site_tmplvar_contentvalues t2 ON t1.contentid = t2.content_id
WHERE
t1.`value` = 'gmc'
AND t2.`value` = 'tacoma';

Answer 3

You can do this with a group by. This is the most flexible in terms of expressing the conditions. In MySQL, multiple joins will often perform better:
select contentid
from modx_site_tmplvar_contentvalues
group by contentid
having sum(`value` = 'gmc') > 0 and
sum(`value` = 'tacoma') > 0;

Answer 4

This is always false:
`value` = 'gmc' and
`value` = 'tacoma'
Instead, use OR:
`value` = 'gmc' OR
`value` = 'tacoma'
In a condition "and" means "this and this is true at the same time". If you want all foos and all bars, then your condition is "foo OR bar".
EDIT:
To select groups containing your values, you can write subqueries:
SELECT DISTINCT name FROM table WHERE name IN (SELECT name FROM table WHERE value='value1') AND name IN (SELECT name FROM table WHERE value='value2')