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 Teradata  |  Question 21 of 24    Print  
what is explain in teradata?
what is explain and how does it work?


  
Total Answers and Comments: 2 Last Update: February 14, 2008     Asked by: dheeraj reddy chala 
  
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February 07, 2008 02:35:25   #1  
sakthiganesht Member Since: February 2008   Contribution: 5    
RE: what is explain in teradata?
Explain is a fn using which you can find the execution procedure of any query in sql assistant. To use this fn type Explain before any query and run it or press F6 after writing a query. It also gives the estimated time, join confidence and memory needed to execute that query. It's advisable to use explain before executing any complex query.
 
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February 14, 2008 04:23:15   #2  
A4ananth Member Since: February 2008   Contribution: 2    
RE: what is explain in teradata?
 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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what is explain and how does it work? 
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