Question

The SQL query without where statement runs great and outputs good results, but when I include WHERE condition it shows Unknown column ‘date1’ in ‘where clause’. What’s the problem?

SELECT
  IF( e.weekly,
      DATE_ADD(DATE(e.time),
      INTERVAL CEIL(DATEDIFF('2010-04-08', e.time)/7) WEEK ),
   DATE(e.time)) AS `e.date1`,
   `v`.`lat`,
   `v`.`lng` 
FROM `events` AS `e`
INNER JOIN `venues` AS `v` ON e.venue_id = v.id
WHERE e.date1 > '2010-09-01'

Answer 1

You cannot alias a column with <tablename>.<name>. Instead of AS e.date1 you really have to use AS date1.
(If you omit the backticks to create the alias you will get an SQL syntax error.)

But this is only one reason. The other is that aliases can’t be used in WHERE clauses.

From the documentation:

An alias can be used in a query select list to give a column a different name. You can use the alias in GROUP BY, ORDER BY, or HAVING clauses to refer to the column

and

Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined.

But you can use aliases in a HAVING clause:

SELECT
  IF( e.weekly,
    DATE_ADD(DATE(e.time),
    INTERVAL CEIL(DATEDIFF('2010-04-08', e.time)/7) WEEK ),
    DATE(e.time)) AS `date1`,
  `v`.`lat`,
  `v`.`lng` 
FROM `events` AS `e`
INNER JOIN `venues` AS `v` ON e.venue_id = v.id
HAVING date1 > '2010-09-01'

or you repeat the whole IF statement in the where clause.