An aggregate function computes a single result from multiple input rows. It is important to understand the interaction between aggregates and SQL 's WHERE. These functions are useful while performing mathematical calculations, string concatenations, sub-strings etc. SQL functions are divided into two categories. An aggregate function performs calculation on a set of values and return a single value. This tutorial introduces the most commonly used MySQL aggregate.
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As far as NULL is concerned, the following two facts are worth knowing and hardly surprising, I would guess: This goes for any condition on non-aggregate columns. If you specify neither, then the default is ALL. String and BLOB values that aggregate function in sql not look like numbers are interpreted as 0.
The result of avg is always a floating point value as long as at there is at least one non-NULL input even if all inputs are aggregate function in sql. The following two expressions are equivalent: Instead, it is enough to use a non-null constant value.
Otherwise, count the number of rows in the group with non-NULL values in the specified column. MIN column Finds the smallest numerical value in the specified column for all rows in the group.