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The returned result is of FLOAT type.

SQRT is the inverse function of POWER(x, 2), so that SQRT(POWER(x,2)) should return x.

Let’s check this

select 3 x, power(3,2) y, sqrt(power(3,2)) sqrt_y;

x	y	sqrt_y
3	9	3

This is correct. However,

select 3.1 x, power(3.1,2) y, sqrt(power(3.1,2)) sqrt_y;

yields

x	y	sqrt_y
3.1	9.6	3,09838667696593

This unexpected result in most likelihood has to do with a loss of precision when the POWER function result type (which matches the type of the argument, NUMERIC) is implicitly converted to FLOAT.

Indeed,

select SQL_VARIANT_PROPERTY(3.1,'BASETYPE') basetype;

basetype
numeric

When we apply an equivalent conversion to retain the NUMERIC type for the result

select 3.1 x, power(3.1,2) y, power(power(3.1,2),0.5) sqrt_y;

everything works as expected.

x	y	sqrt_y
3.1	9.6	3.1

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