Basically, there is an attribute table and translation table - many translations for one attribute.
I need to select id and value from translation for each attribute in a specified language, even if there is no translation record in that language. Either I am missing some join technique or join (without involving language table) is not working here since the following do not return attributes with non-existing translations in the specified language.
select a.attribute, at.id, at.translation
from attribute a left join attributeTranslation at on a.id=at.attribute
where al.language=1;
So I am using subqueries like this, problem here is making two subqueries to the same table with the same parameters (feels like performance drain unless MySQL groups those, which I doubt since it makes you do many similar subqueries)
select attribute,
(select id from attributeTranslation where attribute=a.id and language=1),
(select translation from attributeTranslation where attribute=a.id and language=1),
from attribute a;
I would like to be able to get id and translation from one query, so I concat columns and get the id from string later, which is at least making single subquery but still not looking right.
select attribute,
(select concat(id,';',title)
from offerAttribute_language
where offerAttribute=a.id and _language=1
)
from offerAttribute a
So the question part.
Is there a way to get multiple columns from a single subquery or should I use two subqueries (MySQL is smart enough to group them?) or is joining the following way to go:
[[attribute to language] to translation] (joining 3 tables seems like a worse performance than subquery).
Yes, you can do this. The knack you need is the concept that there are two ways of getting tables out of the table server. One way is ..
FROM TABLE A
The other way is
FROM (SELECT col as name1, col2 as name2 FROM ...) B
Notice that the select clause and the parentheses around it are a table, a virtual table.
So, using your second code example (I am guessing at the columns you are hoping to retrieve here):
SELECT a.attr, b.id, b.trans, b.lang
FROM attribute a
JOIN (
SELECT at.id AS id, at.translation AS trans, at.language AS lang, a.attribute
FROM attributeTranslation at
) b ON (a.id = b.attribute AND b.lang = 1)
Notice that your real table attribute is the first table in this join, and that this virtual table I've called b is the second table.
This technique comes in especially handy when the virtual table is a summary table of some kind. e.g.
SELECT a.attr, b.id, b.trans, b.lang, c.langcount
FROM attribute a
JOIN (
SELECT at.id AS id, at.translation AS trans, at.language AS lang, at.attribute
FROM attributeTranslation at
) b ON (a.id = b.attribute AND b.lang = 1)
JOIN (
SELECT count(*) AS langcount, at.attribute
FROM attributeTranslation at
GROUP BY at.attribute
) c ON (a.id = c.attribute)
See how that goes? You've generated a virtual table c containing two columns, joined it to the other two, used one of the columns for the ON clause, and returned the other as a column in your result set.
Related
I’ve got quite a few tables with product information. The columns on each table that I’m pulling from in this particular query have the exact same column names. I’ve been attempting to do it via a UNION ALL but for some reason it is throwing an error saying non-object but all the column names are correct.
I’m using a format that I found online. But obviously something is wrong. There are more tables; however, this is how it starts (with 2). I’d prefer not to have to code each select statement in the union with unique table abbreviations if I don’t have to.
I don’t have to use union if there is a better method.
All tables share data on Product_Categories and Product_Sub_Category.
The only thing unique to each table is id and part_number.
SELECT f.id,f.part_number,f.cat,f.subcat,f.table_name FROM
(
SELECT t.id,t.part_number,psc.name as subcat,c.name as cat, c.table_name FROM Steel_Strapping as t JOIN Product_Sub_Category as psc ON t.subcat = psc.id JOIN Product_Categories as c ON psc.category = c.id ORDER BY c.sort_order,psc.sort_order,t.sort_order
UNION ALL
SELECT t.id,t.part_number,psc.name as subcat,c.name as cat, c.table_name FROM Product as t JOIN Product_Sub_Category as psc ON t.subcat = psc.id JOIN Product_Categories as c ON psc.category = c.id ORDER BY c.sort_order,psc.sort_order,t.sort_order
) f
My end result is one full list of all products sharing column names. Ex: $result[‘part_number’] will pull part numbers from ALL tables listed in union.
I found the solution when playing around with code. I had to add parenthesis (select...) UNION JOIN (select...) inside the parent select statement
When I want to select all columns expect foo and bar, what I normally do is just explicitly list all the other columns in select statement.
select a, b, c, d, ... from ...
But if table has dozen columns, this is tedious process for simple means. What I would like to do instead, is something like the following pseudo statement:
select * except(foo, bar) from ...
I would also like to know, if there is a function to filter out rows from the result consisting of multiple columns, if multiple rows has same content in all corresponding columns. In other words duplicate rows would be filtered out.
------------------------
A | B | C
------------------------ ====> ------------------------
A | B | C A | B | C
------------------------ ------------------------
You can query INFORMATION_SCHEMA db and get the list of columns (except two) for that table, e.g.:
SELECT REPLACE(GROUP_CONCAT(COLUMN_NAME), '<foo,bar>,', '')
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = '<your_table>' AND TABLE_SCHEMA = '<database>';
Once you get the list of columns, you can use that in your select query.
You can create view based on this table with all columns except these two columns and then use this view everytime with
select * from view
simple group by on all column will remove such duplicates. there are other options as well - distinct and row_number.
select * except(foo, bar) from
This is a frequently requested feature on SO. However, it has not made it to the SQL Standard and I don't know of any SQL products that support it. I guess when the product managers ask their developers, MVPs, usergroups, etc to measure enthusiasm for this prospective feature, they mostly hear, "SELECT * FROM is considered dangerous, we need to protect new users who don't know what they are doing, etc."
You may find it useful to use NATURAL JOIN rather than INNER JOIN etc which removes what would be duplicated columns from the resulting table expression e.g.
SELECT *
FROM Table1 t1
INNER JOIN Table2 t2
ON t1.foo = t2.foo
AND t1.bar = t2.bar;
will result in two columns named foo and two named bar (and possibly other repeated names), probably de-duplicated in some way e.g. by suffixing the range variable names t1 and t2 that INNER JOIN forced you into using.
Whereas:
SELECT *
FROM Table1 NATURAL JOIN Table2;
doesn't require the use of range variables (a good thing) because there will only be one column named foo and one named bar in the result.
And to remove duplicated rows as well as columns changed the implied SELECT ALL * into the explicit SELECT DISTINCT * e.g.
SELECT DISTINCT *
FROM Table1 NATURAL JOIN Table2;
Doing this may reduce your need for the SELECT ALL BUT { these columns } feature you desire.
Of course, if you do that you will be told, "NATURAL JOIN is considered dangerous, we need to protect you from yourself in case you don't know what you are doing, etc." :)
How can i use in table field values in the url
SQL Query wherein all 3 tables are joined
select * from nfojm_usedcar_variants cv
inner join nfojm_usedcar_products cp
inner join nfojm_usedcar_categories cc on
cc.id=cp.prod_cat_id and
cp.id=cv.v_prod_id and
cv.state='1' order by cv.id desc
Output as checked
Then it combines all 3 tables
nfojm_usedcar_variants
nfojm_usedcar_products
nfojm_usedcar_categories
However - all 3 tables have unique field i.e id (but with different values)
I need to pass on value of id and v_prod_id in a url
say url been :-
<a href="index.php?option=com_usedcar&pid='.$row->v_prod_id.'&vid='.$row->id.'">
But id been common field in most of the tables hence its not picking in correctly from nfojm_usedcar_variants,
Can some one help to modify a function so as to fetch in value of id and v_prod_id from the respective table of nfojm_usedcar_variants
thanks
If you have multiple tables in a join that share a common column name, and you need them, then alias them. Such as:
select a.id as aid,a.theName,b.id as bid,b.year
from tableA a
join tableB b
on b.id=a.id
then refer to those columns as aid and bid in your code that follows.
Try to avoid Ever doing a select *. Be explicit. You never know what comes flying out of a select * typically. And odds are you don't need it all. Select * is fine for messing around, but not for production code. And you can't control common column names with select *. We like to control things afterall, no?
I'll try to explain my problem. I have two tables. In the first one each record is identified by a unique INT code (counter). In the second the code from the first table is one of the fields (and may be repeated in various records).
I want to make a SELECT CODE in the second table, based on WHERE parameters, knowing I will get as result a recordset with possibly repeated CODES, and use this recordset for another SELECT in the first table, WHERE CODE IN the above recordset (from the second table).
Is this possible ?? And if yes, how to do this ?
Usually, if I use the WHERE IN clause, the array can contain repeated values like WHERE Code IN "3,4,5,6,3,4,2" ... right ? The difference here is that I want to use a previously Selected recordset in place of the array.
Is this possible ?? Sure is.
And if yes, how to do this ? Like most questions answers depends. There's more than one way to skin this cat; and depending on data (volume of records), and indexes answers can vary.
You can use a distinct or group by to limit the table A records because the join from A--> b is a 1--> many thus we need to distinct or group by the values from A as they would be repeated. But if you need values from B as well, this is the way to do it.
Select A.Code, max(count B.A_CODE) countOfBRecords
from B
LEFT JOIN A
on A.Code = B.A_Code
WHERE B.Paramater = 'value'
and B.Paramater2 = 'Value2'
group by A.Code)
Or using your approach (works if you ONLY need values/columns from table A.)
Select A.Code
from A
Where code in (Select B.A_CODE
From B WHERE B.Paramater = 'value'
and B.Paramater2 = 'Value2')
But these can be slow depending on data/indexes.
You don't need the distinct on the inner query as A.Code only exists once and thus wouldn't be repeated. It's the JOIN which would cause the records to repeat not the where clause.
-Correlated Subquery will return a single A.Code works if you ONLY need values from table A.
Select A.Code
From A
Where exists (Select 1
from B
where b.paramter = value ...
AND A.Code = B.A_CODE)
Since there's no join no A.records would be repeated. On larger data sets this generally performs better .
This last approach works because it Correlates the outer table with sub select Note this can only go 1 level in a relationship. If you had multiple levels deep trying to join this way, it woudln't work.
I need to gather posts from two mysql tables that have different columns and provide a WHERE clause to each set of tables. I appreciate the help, thanks in advance.
This is what I have tried...
SELECT
blabbing.id,
blabbing.mem_id,
blabbing.the_blab,
blabbing.blab_date,
blabbing.blab_type,
blabbing.device,
blabbing.fromid,
team_blabbing.team_id
FROM
blabbing
LEFT OUTER JOIN
team_blabbing
ON team_blabbing.id = blabbing.id
WHERE
team_id IN ($team_array) ||
mem_id='$id' ||
fromid='$logOptions_id'
ORDER BY
blab_date DESC
LIMIT 20
I know that this is messy, but i'll admit, I am no mysql veteran. I'm a beginner at best... Any suggestions?
You could put the where-clauses in subqueries:
select
*
from
(select * from ... where ...) as alias1 -- this is a subquery
left outer join
(select * from ... where ...) as alias2 -- this is also a subquery
on
....
order by
....
Note that you can't use subqueries like this in a view definition.
You could also combine the where-clauses, as in your example. Use table aliases to distinguish between columns of different tables (it's a good idea to use aliases even when you don't have to, just because it makes things easier to read). Example:
select
*
from
<table> as alias1
left outer join
<othertable> as alias2
on
....
where
alias1.id = ... and alias2.id = ... -- aliases distinguish between ids!!
order by
....
Two suggestions for you since a relative newbie in SQL. Use "aliases" for your tables to help reduce SuperLongTableNameReferencesForColumns, and always qualify the column names in a query. It can help your life go easier, and anyone AFTER you to better know which columns come from what table, especially if same column name in different tables. Prevents ambiguity in the query. Your left join, I think, from the sample, may be ambigous, but confirm the join of B.ID to TB.ID? Typically a "Team_ID" would appear once in a teams table, and each blabbing entry could have the "Team_ID" that such posting was from, in addition to its OWN "ID" for the blabbing table's unique key indicator.
SELECT
B.id,
B.mem_id,
B.the_blab,
B.blab_date,
B.blab_type,
B.device,
B.fromid,
TB.team_id
FROM
blabbing B
LEFT JOIN team_blabbing TB
ON B.ID = TB.ID
WHERE
TB.Team_ID IN ( you can't do a direct $team_array here )
OR B.mem_id = SomeParameter
OR b.FromID = AnotherParameter
ORDER BY
B.blab_date DESC
LIMIT 20
Where you were trying the $team_array, you would have to build out the full list as expected, such as
TB.Team_ID IN ( 1, 4, 18, 23, 58 )
Also, not logical "||" or, but SQL "OR"
EDIT -- per your comment
This could be done in a variety of ways, such as dynamic SQL building and executing, calling multiple times, once for each ID and merging the results, or additionally, by doing a join to yet another temp table that gets cleaned out say... daily.
If you have another table such as "TeamJoins", and it has say... 3 columns: a date, a sessionid and team_id, you could daily purge anything from a day old of queries, and/or keep clearing each time a new query by the same session ID (as it appears coming from PHP). Have two indexes, one on the date (to simplify any daily purging), and second on (sessionID, team_id) for the join.
Then, loop through to do inserts into the "TempJoins" table with the simple elements identified.
THEN, instead of a hard-coded list IN, you could change that part to
...
FROM
blabbing B
LEFT JOIN team_blabbing TB
ON B.ID = TB.ID
LEFT JOIN TeamJoins TJ
on TB.Team_ID = TJ.Team_ID
WHERE
TB.Team_ID IN NOT NULL
OR B.mem_id ... rest of query
What I ended up doing is;
I added an extra column to my blabbing table called team_id and set it to null as well as another field in my team_blabbing table called mem_id
Then I changed the insert script to also insert a value to the mem_id in team_blabbing.
After doing this I did a simple UNION ALL in the query:
SELECT
*
FROM
blabbing
WHERE
mem_id='$id' OR
fromid='$logOptions_id'
UNION ALL
SELECT
*
FROM
team_blabbing
WHERE
team_id
IN
($team_array)
ORDER BY
blab_date DESC
LIMIT 20
I am open to any thought on what I did. Try not to be too harsh though:) Thanks again for all the info.