Cast string to number, interpreting null or empty string as 0

Question

I have a Postgres table with a string column carrying numeric values. I need to convert these strings to numbers for math, but I need both NULL values as well as em

Answer 1

You could also use

cast(
    case
        when coalesce(orig, '') = '' then '0'
        else orig
    end
    as float
)

You could also unwrap that a bit since you're being fairly verbose anyway:

cast(
    case
        when orig is null then '0'
        when orig = '' then '0'
        else orig
    end
    as float
)

or you could put the cast inside the CASE:

case
    when coalesce(orig, '') = '' then 0.0
    else cast(orig as float)
end

A CASE makes it a bit easier to account for any other special conditions, this also seems like a clearer expression of the logic IMO. OTOH, personal taste and all that.