SQL INNER JOIN看不到表别名

Question

I'm having trouble with this SQL statement:

SELECT linkstable.date, (linkstable.count - x.count) 
FROM (SELECT .....) AS linkstable 
INNER JOIN linkstable AS x 
  ON linkstable.date = x.date+1 

It tells me that links table cannot be found although (SQL error 1146) there clearly is an alias to that select query. Can anybody tell me please how do I bypass this error?

Answer 1

You cannot alias an alias. If you want to join table to itself, repeat the select:

SELECT linkstable.date, (linkstable.count - x.count) 
FROM (SELECT .....) AS linkstable 
INNER JOIN (SELECT .....) AS x ON linkstable.date = x.date+1

If inner select is too cumbersome or you're running into performance issues insert its results into a temp table and use it in your main query.

Answer 2

You can't reference a subquery's alias in the FROM clause like that. However, if your database supports Common Table Expressions, you can use the WITH clause to accomplish the same thing:

WITH linkstable as (SELECT ...)
SELECT linkstable.date, (linkstable.count - x.count) 
FROM linkstable 
INNER JOIN linkstable AS x 
  ON linkstable.date = x.date+1