I have 3 tables that need to be dealt with in a SQL query. If it comes to it, technically I'm working with a MySQL database, but I'm pretty sure that any of the SQL-utilizing DMBS that I've picked for my categories should be able to work with the same answer.
Anyway, the first table is called "templates" the second is called "tempXcat" and the third is "categories". Their purposes should seem obvious enough. There is a many-to-many relationship between templates and categories, so tempXcat is my crossover table. Now, my question is, how do I construct a statement that identifies all templates NOT represented in the crossover table? I need the same thing for all categories not represented in the crossover table.
I'm fairly certain this is basic SQL stuff, but I'm self-taught, so my instruction has some gaping holes, and I don't know what I'd be looking for if I were to search the manual. Your help will be greatly appreciated. Thanks!
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Lets say Template and category both have primary keys called ID and TempXcat has columns called TemplateID and CategoryID
SELECT template.* FROM template LEFT JOIN TempXCat on template.id=TempXCat.Templ
SELECT category.* FROM category LEFT JOIN TempXCat on category.id=TempXCat.categ
Or
SELECT Template.* from template where template.id not in (select templateID from TempXCat)
SELECT * from category where id not in (select categoryID from TempXCat)
Regards
Tushar
Business Accounts
Answer for Membership
by: ee_rleePosted on 2008-04-20 at 08:26:53ID: 21396382
hi, you can do it in at least 3 ways
1. Using left join (I prefer this one) . When the ID in templates does not match in tempXcat, all values on tempXcat will return NULL.
SELECT t.*
FROM templates t LEFT JOIN
tempXcat x ON t.TemplateID=x.TemplateID
WHERE x.TemplateID IS NULL
2. Using not exists. Checks if an ID in templates does not exist in tempXcat.
SELECT *
FROM templates t
WHERE NOT EXISTS (SELECT 1 FROM tempXcat WHERE TemplateID=t.TemplateID)
3. Using not in. The subquery returns a list of IDs from tempXcat and the not in statement returns records from templates not in the list.
SELECT *
FROM templates t
WHERE TemplateID NOT IN (SELECT DISTINCT TemplateID FROM tempXcat)
> I need the same thing for all categories not represented in the crossover table.
Just change templates to categories and their corresponding id/linked fields.