Typecast to a FLOAT - casting

Question

The following query was not returning my expected/desired results for slope and intercept. I finally realized that slope and intercept are typecasted as integers in my anchor query, and remain integers through the recursion.
WITH RECURSIVE t AS (
SELECT id parentId, idPublic parentIdPublic, name parentName,
slope parentSlope, intercept parentIntercept,
id, idPublic, name, type, 1 slope, 0 intercept, value
FROM measurements
WHERE id IN (414,415,416,417,491)
UNION ALL
SELECT t.parentId, t.parentIdPublic, t.parentName,
t.parentSlope, t.parentIntercept,
m.id, m.idPublic, m.name, m.type,
t.slope*pchm.sign*m.slope slope,
t.intercept+t.slope*pchm.sign*m.intercept intercept, m.value
FROM t
INNER JOIN subpoints sp ON sp.measurementId=t.id
INNER JOIN measurements m ON m.id=sp.measurementId
)
SELECT slope, intercept FROM t;
slope and intercept needs to be able to store widely different values and exact accuracy is not important, so I feel a FLOAT is best. My schema for slope and intercept is as shown:
`slope` FLOAT NOT NULL DEFAULT 1,
`intercept` FLOAT NOT NULL DEFAULT 0,
As a hack solution, I changed my anchor query to:
SELECT id parentId, ..., 1.0 slope, 0.0 intercept, value
I think the right solution is to typecase these two values to a FLOAT, but the documentation does not seem to allow. I could do DECIMAL, however, I have the issue with slope and intercept potentially being a wide range of values.
Am I able to cast slope and intercept to FLOAT? If not, what is the best solution?

Answer 1

I think that UNION is the villain, not WITH, etc. UNION likes to define the datatypes based on the first SELECT. Of course, with WITH RECURSIVE, you don't have the option of swapping the SELECTs.
So... I vote for your 'hack solution' of 0.0 and 1.0. Or, these might be clearer: 0e0 and 1e0. (Still a kludge, but it points at FLOAT, not DECIMAL.)
I, too, have bemoaned the absence of CASTing to FLOAT (or DOUBLE).