Example of coalesce operator - sql, PL-SQL Programming

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Example of COALESCE operator

Example: Give the total of marks for each exam (simplified solution)

SELECT CourseId,

COALESCE ((SELECT SUM (Mark)

FROM EXAM_MARK AS EM

WHERE EM.CourseId = C.CourseId ),

0) AS TotalMark

FROM COURSE AS C

Explanation

The first operand to the invocation of COALESCE is a scalar subquery similar to Aggregate Operators. Recall the need to enclose the SELECT expression in parentheses, without which it would denote a table rather than a number.

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