WHERE, GROUP BY, and HAVING Clause Evaluation - Teradata Database

WHERE, GROUP BY, and HAVING Clause Evaluation

WHERE, GROUP BY, and HAVING clauses in a SELECT statement are evaluated in this order:

WHERE

GROUP BY

HAVING

Before performing the sort operation that groups the rows to be returned to the requestor, Teradata Database creates a sort key and appends it to the rows to be sorted. If the length of this temporary data structure exceeds the system row length limit of 64 KB, the operation returns an error to the requestor. Depending on the situation, the message text is one of the following:

A data row is too long.

Maximum row length exceeded in database_object_name.

For explanations of these messages, see Messages.

The BYNET only looks at the first 4096 bytes of the sort key created to sort the specified fields, so if the field the sort key is based on is greater than 4096 bytes, the key is truncated and the data might not be returned in the desired order.