SQL Avg() Example
Select Avg(Film_Length) From Film_Table Where Film_Title in ("Pinocchio", "Hercules", "Mulan", "The Lady and the Tramp", "The Little Mermaid");
85 (in minutes)
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|Comment by TheMadProfessor on 2013-07-06 Rate this Comment|
A Gotcha to keep in mind for column functions in general is that for aggregate function computations other than COUNT(*), rows containing NULL are excluded. A common misconception I've seen is expecting NULL to be equated to a value of zero, when instead it is simply ignored. For example, if a sixth movie was added to the IN values above that had a NULL for film length, you would get the same result as above computed by (80+90+90+80+85)/5, instead of (80+90+90+80+85+0)/6. The rows containing NULL values are completely ignored in the computation.
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