SQL Query to get only 1 instance of a record where one to many relationship exists - sql

Question

Ive got an SQL Query trying to get 1 record back when a 1 to many relationship exists.
SELECT dbo.BlogEntries.ID AS blog_entries_id, dbo.BlogEntries.BlogTitle, dbo.BlogEntries.BlogEntry, dbo.BlogEntries.BlogName,
dbo.BlogEntries.DateCreated AS blog_entries_datecreated, dbo.BlogEntries.inActive AS blog_entries_in_active,
dbo.BlogEntries.HtmlMetaDescription AS blog_entries_html_meta_description, dbo.BlogEntries.HtmlMetaKeywords AS blog_entries_html_meta_keywords,
dbo.BlogEntries.image1, dbo.BlogEntries.image2, dbo.BlogEntries.image3, dbo.BlogEntries.formSelector, dbo.BlogEntries.image1Alignment,
dbo.BlogEntries.image2Alignment, dbo.BlogEntries.image3Alignment, dbo.BlogEntries.blogEntryDisplayName, dbo.BlogEntries.published AS blog_entries_published,
dbo.BlogEntries.entered_by, dbo.BlogEntries.dateApproved, dbo.BlogEntries.approved_by, dbo.blog_entry_tracking.id AS blog_entry_tracking_id,
dbo.blog_entry_tracking.blog, dbo.blog_entry_tracking.blog_entry, dbo.BlogCategories.ID, dbo.BlogCategories.BlogCategoryName,
dbo.BlogCategories.BlogCategoryComments, dbo.BlogCategories.DateCreated, dbo.BlogCategories.BlogCategoryTitle, dbo.BlogCategories.BlogCategoryTemplate,
dbo.BlogCategories.inActive, dbo.BlogCategories.HtmlMetaDescription, dbo.BlogCategories.HtmlMetaKeywords, dbo.BlogCategories.entry_sort_order,
dbo.BlogCategories.per_page, dbo.BlogCategories.shorten_page_content, dbo.BlogCategories.BlogCategoryDisplayName, dbo.BlogCategories.published,
dbo.BlogCategories.blogParent
FROM dbo.BlogEntries LEFT OUTER JOIN
dbo.blog_entry_tracking ON dbo.BlogEntries.ID = dbo.blog_entry_tracking.blog_entry LEFT OUTER JOIN
dbo.BlogCategories ON dbo.blog_entry_tracking.blog = dbo.BlogCategories.ID
i have some records assigned to 2 different blogcategories, and when i query everything it returns duplicate records.
How do i only return 1 instance of a blog?

Answer 1

Try this one -
SELECT blog_entries_id = be.Id
, be.BlogTitle
, be.BlogEntry
, be.BlogName
, blog_entries_datecreated = be.DateCreated
, blog_entries_in_active = be.inActive
, blog_entries_html_meta_description = be.HtmlMetaDescription
, blog_entries_html_meta_keywords = be.HtmlMetaKeywords
, be.image1
, be.image2
, be.image3
, be.formSelector
, be.image1Alignment
, be.image2Alignment
, be.image3Alignment
, be.blogEntryDisplayName
, blog_entries_published = be.published
, be.entered_by
, be.dateApproved
, be.approved_by
, blog_entry_tracking_id = bet.Id
, bet.blog
, bet.blog_entry
, bc2.Id
, bc2.BlogCategoryName
, bc2.BlogCategoryComments
, bc2.DateCreated
, bc2.BlogCategoryTitle
, bc2.BlogCategoryTemplate
, bc2.inActive
, bc2.HtmlMetaDescription
, bc2.HtmlMetaKeywords
, bc2.entry_sort_order
, bc2.per_page
, bc2.shorten_page_content
, bc2.BlogCategoryDisplayName
, bc2.published
, bc2.blogParent
FROM dbo.BlogEntries be
LEFT JOIN dbo.blog_entry_tracking bet ON be.Id = bet.blog_entry
OUTER APPLY (
SELECT TOP 1 *
FROM dbo.BlogCategories bc
WHERE bet.blog = bc.Id
) bc2
Also, I would like to mention that in this case, using of aliases in the column names decreases the size of your query and makes it more convenient for understanding.

Answer 2

if you just need one record back, you can use
SELECT TOP 1 dbo.BlogEntries.ID AS blog_entries_id, dbo.Bl.... (same as you have now).
it is more efficient than SELECT DISTINCT

Answer 3

Here is a Northwind Example.
It will return only 1 row in the Order Detail table for each Order.
Use Northwind
GO
Select COUNT(*) from dbo.Orders
select COUNT(*) from dbo.[Order Details]
select * from dbo.Orders ord
join
(select ROW_NUMBER() OVER(PARTITION BY OrderID ORDER BY UnitPrice DESC) AS "MyRowID" , * from dbo.[Order Details] innerOD) derived1
on ord.OrderID = derived1.OrderID
Where
derived1.MyRowID = 1
Order by ord.OrderID