Question

I have a table which has categories information.

The table has a field to mark the parent and child categories.

I tried to list the parent category then its child category through a query.

I tried something like

SELECT 
  CategoryID.categories as ParentID,
  CategoryName.categories AS ParentName, 
  parents.* 
FROM 
  categories AS parents LEFT JOIN categories AS child 
    ON child.Parent = parents.ParentID

but unfortunately it didn’t work for me. It gives me a weird error.

[SQL] SELECT CategoryID.categories as ParentID, CategoryName.categories 
AS ParentName, parents.* FROM categories as parents LEFT JOIN categories as child on child.Parent = parents.ParentID

[Err] 1054 - Unknown column 'CategoryID.categories' in 'field list'

and I’m sure that all fields name are correct.

Answer 1

First thing is, db engine reads columns [table].[column], not the other way around. So it won’t understand what CategoryID.categories is – there is no table called CategoryID.

You defined your tables as such

     FROM categories AS parents 
LEFT JOIN categories AS child 

So you need to reference them using the names you gave them. i.e.

SELECT
      parents.CategoryId as ParentId,
      child.CategoryId as ChildId,
      ...