In MySQL, the GROUPING() function allows us to identity which rows have been generated by the WITH ROLLUP modifier of the GROUP BY clause.
By default, WITH ROLLUP outputs NULL as the value that represents all aggregate values. By this, I mean it doesn’t provide us with a nice easy to read label. It simply outputs NULL. This makes it more difficult for us to distinguish between normal rows and super aggregate rows that were generated by WITH ROLLUP.
In MySQL, ANY_VALUE() is an aggregate function that allows us to include nonaggregated columns in the SELECT list when using the GROUP BY clause.
The ANY_VALUE() function is commonly used to resolve issues that arise when a query includes columns that are not part of the GROUP BY clause or aggregate functions. It can be useful in scenarios where we want to include descriptive columns in a grouped result set without affecting the grouping behaviour.
In MySQL, the VAR_SAMP() function returns the sample variance of an expression. The denominator is the number of rows minus one.
If there are no matching rows, or if the expression is NULL, VAR_SAMP() returns NULL.
VAR_SAMP() is an aggregate function, and so it can be used with the GROUP BY clause.
The VAR_SAMP() function can also be used as a window function.
In MySQL, the VARIANCE() function returns the population standard variance of an expression.
If there are no matching rows, or if the expression is NULL, the function returns NULL.
The VARIANCE() function is a synonym for the standard SQL VAR_POP() function. In other words, they both do the same thing, but VARIANCE() is not standard SQL. Therefore, if you need to use standard SQL, use VAR_POP() instead.
In MySQL, the VAR_POP() function returns the population standard variance of an expression.
If there are no matching rows, or if the expression is NULL, VAR_POP() it returns NULL.
VAR_POP() is an aggregate function, and so it can be used with the GROUP BY clause.
The VAR_POP() function is standard SQL. There’s also a VARIANCE() function that does the same thing, but is not standard SQL.
In MySQL, the STDDEV_SAMP() function returns the sample standard deviation of a given expression. This is the square root of VAR_SAMP().
STDDEV_SAMP() is an aggregate function, and so it can be used with the GROUP BY clause.
If there are no matching rows, or if the expression is NULL, STDDEV_SAMP() returns NULL.
In MySQL, the STDDEV() function returns the population standard deviation of a given expression.
STDDEV() is a synonym for the standard SQL function STDDEV_POP(). There’s also a STD() function which also does the same thing, so we can use either of these functions to get the same result.
In MySQL, the STD() function returns the population standard deviation of a given expression.
STD() is a synonym for the standard SQL function STDDEV_POP(). There’s also a STDDEV() function which also does the same thing, so we can use either of these functions to get the same result.