Question

I’m trying the following SQL query:

  select (execution_end_timestamp - execution_queued_timestamp) as totalTime, execution_queued_timestamp from exec_queue
  where execution_name like '%Generate%'
  and execution_queued_timestamp > '2012-10-04 20:00:00.000'
  having totalTime < '1900-01-01 00:00:06.000'

I’ve tried using the totalTime in the where and having clause and in both cases it doesn’t work. I also tried datediff hoping that might work, but it had identical results.

Is there a trick where you can use a computed field in a where or having clause? Googling around hasn’t turned up anything except in cases where an aggregating function is used.

Answer 1

No, alias is not allowed on WHERE clause, try,

select (execution_end_timestamp - execution_queued_timestamp) as totalTime, execution_queued_timestamp 
from exec_queue
where execution_name like '%Generate%' AND
      execution_queued_timestamp > '2012-10-04 20:00:00.000' AND
      (execution_end_timestamp - execution_queued_timestamp) < '1900-01-01 00:00:06.000'

Reason why ALIAS doesn’t work on WHERE and HAVING clause,

• First the product of all tables in the from clause is formed.
• The where clause is then evaluated to eliminate rows that do not satisfy the search_condition.
• Next, the rows are grouped using the columns in the group by clause.
• Then, Groups that do not satisfy the search_condition in the having clause are eliminated.
• Next, the expressions in the select clause target list are evaluated.
• If the distinct keyword in present in the select clause, duplicate rows are now eliminated.
• The union is taken after each sub-select is evaluated.
• Finally, the resulting rows are sorted according to the columns specified in the order by clause.