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What is explain and how does it work?


The EXPLAIN facility is a teradata extension that provides you with an "ENGLISH" translation of the steps choosen by the optimizer to execute an SQL

statement.It may be used oin any valid teradata database with a preface called "EXPLAIN".

The following is an example:-

EXPLAIN select last_name,first_name FROM employees;

The EXPLAIN parses the SQL statement but does not execute it.

This provides the designer with an "execution stratergy".

The execution stratergy provides what an optimizer does but not why it choses them.

The EXPLAIN facility is used to analyze all joins and complex queries.

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