Fernando Nasser of Red Hat pointed out to me that we are not quite spec-compliant on the FLOAT(p) datatype notation. We interpret P as the number of decimal digits of precision, and hence translate

P = 1..6 => float4 (a/k/a REAL) P = 7..15 => float8 (a/k/a DOUBLE PRECISION) otherwise error However, the spec is perfectly clear that P is to be interpreted as the number of *binary* digits of precision, not decimal digits. SQL92 section 4.4.1 says: An approximate numeric value consists of a mantissa and an expo- nent. The mantissa is a signed numeric value, and the exponent is a signed integer that specifies the magnitude of the mantissa. An approximate numeric value has a precision. The precision is a posi- tive integer that specifies the number of significant binary digits ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ in the mantissa. The value of an approximate numeric value is the mantissa multiplied by 10^exponent. So it's fairly clear that P is not the number of decimal digits. (The reference to multiplying by 10^exponent seems bogus, since on machines where the mantissa is in fact binary, one would expect a base-2 or possibly base-16 exponent to be used. But this does not affect the precision of the mantissa AFAICS.) On the assumption that most platforms have IEEE float math, it would be appropriate to interpret P like this: P = 1..24 => float4 P = 25..53 => float8 otherwise error This is a straightforward change and would not break pg_dump files, since fortunately pg_dump always references the underlying types and never refers to anything as FLOAT(p). But I wonder whether it is likely to break many existing applications. There is a hazard of some existing app asking for (what it thinks is) float8 and getting float4 instead. Is it worth trying to provide some sort of backwards-compatibility mode? We could imagine adding a GUC variable to select binary or decimal precision, but I really don't want to. It would increase the amount of work needed by more than an order of magnitude, and this problem doesn't seem worth it. I'd rather just list this under Incompatibilities in the 7.4 release notes. Comments? regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]