I have a column ContentID in a table that identifies content that exists in other tables. For example, it could refer to a pageID, productID, etc. My plan is to use that to pull through other information I need, such as a page name or product name. This is what I have so far:
SELECT TL.ID, TL.TableName, TL.FileName, TL.ContentID, p.PageName AS Content
FROM TranslationLog TL
LEFT JOIN Pages P ON TL.ContentID = P.PageID
LEFT JOIN Categories C ON TL.ContentID = C.CategoryID
LEFT JOIN ProductDescriptions PD ON TL.ContentID = PD.SKU
The idea is for each row, I want to get the data for the specified content using the TableName and ContentID fields. Currently, I'm able to get PageName by selecting p.PageName AS Content. However, I'd like to do this for each of the tables; if the row corresponds to the pages table, then query that table - same for categories and product descriptions. I also need it to have the alias "Content", regardless of which field from another table we're using, such as PageName or ProductName.
Is it possible to do this?
EDIT:
The solution posted by rd_nielsen was almost perfect, but it turned out there was actually a bit of overlap with the ContentID. Here's what I ended up with to fix it:
SELECT TL.ID, TL.TableName, TL.FileName, TL.ContentID, coalesce(P.PageName, C.CategoryName, PD.ProductName)
FROM TranslationLog TL
LEFT JOIN Pages P ON TL.ContentID = P.PageID AND TL.TableName = 'Pages'
LEFT JOIN Categories C ON TL.ContentID = C.CategoryID AND TL.TableName = 'Categories'
LEFT JOIN ProductDescriptions PD ON TL.ContentID = PD.SKU AND TL.TableName = 'Products'
You should use cross-apply. For example:
select
T.*
from
table_stored_data u
cross apply dbo.created_function(u.contentid,u.tablename,u.search_column) T
You need to write a function for it.
If the values of TranslationLog.ContentID can appear in only one of the related tables, then you can coalesce the values from those tables:
SELECT
TL.ID,
TL.TableName,
TL.FileName,
TL.ContentID,
coalesce(p.PageName, C.CategoryName, PD.ProductName) AS Content
FROM
...
Try concat function:
select concat(p.PageName, C.CategoryName, PD.ProductName) AS Content from ...
Related
I have a task in which I'm using Northwind database to select only these products which category name begins with 'C'. Product details are in table Products while CategoryName is in table Categories and this is the only answer I came up with
SELECT P.*
FROM Products P, Categories C
WHERE C.CategoryName LIKE 'C%' AND P.CategoryID = C.CategoryID
I was curious if I can do it without putting Categories inside FROM clause and connecting the tables. For me it seemed logical that I can access child table and use the values inside it smh, can you explain why it's not possible?
You can use a Correlated Subquery to achieve this:
SELECT *
FROM Products p
WHERE EXISTS (SELECT id FROM Categories c WHERE c.id = p.id)
This subquery is "Correlated" in that the SQL in the subquery references the query in which it's contained. Very similar to a join, but we are down in the WHERE clause using the EXISTS condition.
EXISTS is nice since it doesn't care what is returned by the subquery. It only cares that ANYTHING was returned by the subquery. So that subquery could also be: SELECT 1 FROM Categories WHERE c.id = p.id and this query would still work.
You should be using JOINS not that type of syntax (INNER, LEFT, RIGHT, ...)
But you can do this
SELECT P.*
FROM dbo.Products P WITH (NOLOCK)
INNER JOIN dbo.Categories C WITH (NOLOCK)
ON P.CategoryID = C.CategoryID
WHERE
SUBSTRING(LTRIM(C.CategoryName), 1, 1) = 'C'
Join Products with Categories using an INNER JOIN which will only return the records that match. Add WITH (NOLOCK) when selecting from a transactional database so it does not lock users when attempting to run a transaction. I try to avoid LIKE when possible so in your scenario you can use substring to get the first character. The first argument is the expression, then start index and then how many characters you need to grab. LTRIM will remove white spaces from the left so even if your CategoryName accidentally has a leading whitespace or spaces it will remove them before running the substring. RTRIM would be unnecessary for what you need
I am working on a query that has fields called ios_app_id, android_app_id and app_id.
The app_id from downloads table can be either ios_app_id or android_app_id in the products table.
Is it correct that because of that I cannot just run a simple join of downloads and products table on on p.ios_app_id = d.app_id and then join again on on p.android_app_id = d.app_id? Would that cause an incorrect number of records?
select p.product_id, d.date, d.downloads,
from products p
inner join download d
on p.ios_app_id = d.app_id
UNION
select p.product_id, d.date, d.downloads
from products p
inner join download d
on p.android_app_id = d.app_id
I would try:
select p.product_id, d.date, d.downloads,
from products p
inner join downloads d
on p.ios_app_id = d.app_id
inner join downloads d
on p.android_app_id = d.app_id
Basically I am trying to understand why the union here is needed instead of just joining the two fields twice? Thank you
Just join twice:
select p.product_id,
coalesce(di.date, da.date),
coalesce(di.downloads, da.downloads)
from products p left join
downloads di
on p.ios_app_id = di.app_id left join
downloads da
on p.android_app_id = da.app_id;
This should be more efficient than your method with union. Basically, it attempts joining using the two ids. The coalesce() combines the results into a single column.
Remember that the purpose of an INNER JOIN is to get the values that exists on BOTH sets of data (lets called them table A and table B), using a specific column to join them. In your example, if you try to do the INNER JOIN twice, what would happen is that the first time you execute the INNER JOIN, the complete PRODUCTS table is your table A, and you obtain all the products that have downloaded the ios_app, but now (and this is the key part) this result becomes your new dataset, so it becomes your new table A for the next inner join. And thats the issue, cause what you would want is to join the whole table again, not just the result of the first join, but thats not how it works. This is why you need to use the UNION, cause you need to obtain your results independently and then add them.
An alternative would be to use LEFT JOIN, but you could get null values and duplicates -and its not too "clean"-. So, for your particular case, I think using UNION is much clearer and easier to understand.
If you do left join in first query it will work.
create table all_products as (select p.product_id, d.date, d.downloads,
from products p
left join downloads d
on p.ios_app_id = d.app_id)
select a.product_id, d.date, d.downloads from all_products a left join downloads d
on a.android_app_id = d.app_id inner join
I managed to import too much data into one of my database tables. I want to delete most of this data, but I need to ensure that the reference doesn't exist in either of two other tables before I delete it.
I figured this query would be the solution. It give me the right result on a test database, but in the production environment it returns no hits.
select product
from products
where 1=1
and product not in (select product from location)
and product not in (select product from lines)
You are getting no results/hits it means that you table location and/or lines having the null values in the product column. in clause failed if column having null value.
try below query just added the null condition on the top of your shared query.
select product from products
where 1=1
and product not in ( select product from location where product is not null)
and product not in ( select product from lines where product is not null)
Use EXISTS instead of IN which is more efficient
DELETE FROM products WHERE
NOT EXISTS
(
SELECT
1
FROM [Location]
WHERE Product = Products.Product
) AND
NOT EXISTS
(
SELECT
1
FROM lines
WHERE Product = Products.Product
)
Try this..
DELETE FROM Products where not exists
(select 1 from Location
join lines on lines.Product = Location.Product
and Location.Product = Products.Product
);
It's difficult to tell from your post why the query would return results in the test database but not production other than there is different data or different structures. You might try including the DDL for the participating tables in your post so that we know what the table structures are. For example, is the "product" column a PK or a text name?
One thing that does jump out is that your query will probably perform poorly. Try something like this instead: (Assuming the "product" column is a PK in Products and FK in the other tables.)
Select product
From Products As p
Left Outer Join Location As l
On p.product = l.product
And l.product is null
Left Outer Join Lines as li
On p.product = li.product
And li.product is null;
This simple set based approach may help ...
DELETE p
FROM products p
LEFT JOIN location lo ON p.product = lo.product
LEFT JOIN lines li ON p.product = li.product
WHERE lo.product IS NULL AND li.product IS NULL
I have three tables:
COLLECTION
PERSON
PERSON_COLLECTION
where PERSON_COLLECTION is a mapping table id|person_id|collection_id
I now want to select all entries in collection and order them by person.name.
Do I have to join the separate tables with the mapping table first and then do a join again on the results?
SELECT
c.*,
p.Name
FROM
Collection c
JOIN Person_Collection pc ON pc.collection_id = c.id
JOIN Person p ON p.id = pc.person_id
ORDER BY p.Name
Not sure without the table schema but, my take is:
SELECT
c.*,
p.*
FROM
Person_Collection pc
LEFT JOIN Collection c
ON pc.collection_id = c.id
LEFT JOIN Person p
ON pc.person_id = p.id
ORDER BY p.name
The order you join won't break it but depending on which sql product you're using may effect performance.
You need to decide if you want ALL records from both/either table or only records which have a matching mapping entry, this will change the type of join you need to use.
I'm beginner and I need help!!!!!
I have a database:
article: id, name, description, id_pic, lang, date
category: id_cat, name_cat
pictures: id_pic, image
sub_cat: id_subcat, name_subcat, id_cat
I need to SELECT name, desc, image, name_subcat this on
SELECT
a.id, a.name, a.desc, sc.name_subcat, p.picture, a.id_subcat
FROM
article a, subcategory sc
LEFT JOIN
pictures p ON a.id_pic = p.id_pic
WHERE
a.id_subcat = sc.id_subcat
AND a.id_subcat IN (SELECT sc.id_subcat
FROM subcategory sc
WHERE id_cat = (SELECT id_cat
FROM category
WHERE name_cat = '???????'))
Try this:
SELECT a.id, a.name, a.desc,
sc.name_subcat, p.picture, a.id_subcat
FROM article a,
LEFT JOIN subcategory sc ON a.id_subcat = sc.id_subcat
LEFT JOIN categories c ON sc.id_cat = c.id_cat
LEFT JOIN pictures p ON a.id_pic = p.id_pic
WHERE c.name_cat = '??????'
Just join the table subcategory with other tables instead of where a.id_subcat = sc.id_subcat. This join will ensure that any a.id_subcat is in subcategory, so you can get rid of the subquery in the where clause too. You will also need to join the categories c table too.
You will need to choose the JOIN type whether left ot INNER, depending on what data to select from your table.
You seem to be missing some joins defines.
Four tables:
Article:
ID
Name
Description
ID_Pic
Lang
Date
Category:
id_cat
name_cat
Subcategory:
id_subcat
name_subcat
id_cat
Pictures:
id_pic
image,
We need to see how Category/Subcategory relate to articles. Do articles have a category they are linked to that you are missing afield from?
When you can get me these answers i can go through a join process for you.
EDIT: I see the missing field. Please ignore, good answer above me.
Regards,
Jason