Scalar Subquery

A scalar row subquery is a single-row subquery. In other words, it returns a single row. If the scalar subquery returns more than one row, it generates an error. The Oracle 9i version has more support of scalar subqueries than Oracle 8i.

▪ FOR EXAMPLE

SELECT city, state, 
      (SELECT count(*) 
         FROM student s 
        WHERE s.zip = z.zip) as student_count 
  FROM zipcode z 
 WHERE state = 'CT'

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