6.2

The Subquery in an UPDATE statement

The Subquery in an UPDATE statement

  • Subqueries may be used in an UPDATE statement
  • Since it is possible to change many values at once with a subquery, take special care before running an UPDATE statement with a subquery. You might make a copy of the table and data you are trying to change to test with before running your statement on live data.
  • It is also possible to run your UPDATE statement inside of a transaction block that allows you to ROLLBACK or undo a statement. We will address the topic of ROLLBACK in a future lesson.

Code Sample:

1    UPDATE country 
2    SET GNPOld = 0.00 
3    WHERE Code IN 
4    (SELECT CountryCode FROM countrylanguage WHERE population = 0)

Results:

sub_02.png

UPDATE country

SET GNPOld = 0.00

WHERE Code IN

(SELECT CountryCode FROM countrylanguage WHERE population = 0)

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