Sams Teach Yourself Oracle PLSQL in 10 Minutes by Ben Forta

Author:Ben Forta [Forta, Ben]
Language: eng
Format: azw3
Publisher: Pearson Education
Published: 2015-09-01T16:00:00+00:00

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Correlated Subquery

A subquery that refers to the outer query.

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The type of subquery is called a correlated subquery. This syntax—the table name and the column name separated by a period—must be used whenever there is possible ambiguity about column names. Why? Well, let’s look at what happens if fully qualified column names are not used:

Input

Click here to view code image

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SELECT cust_name,

cust_state,

(SELECT COUNT(*)

FROM orders

WHERE cust_id = cust_id) AS orders

FROM customers

ORDER BY cust_name;

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