PostgreSQL: IN A SINGLE SQL SYNTAX order by numeric value computed from a text column

Question

A column has a string values like \"1/200\", \"3.5\" or \"6\". How can I convert this String to numeric value in single SQL query?

My actual SQL is more complicated, h

Answer 1

I would define a stored function to convert the string to a numeric value, more or less like this:

CREATE OR REPLACE FUNCTION fraction_to_number(s CHARACTER VARYING)
RETURN DOUBLE PRECISION AS
BEGIN
   RETURN
   CASE WHEN s LIKE '%/%' THEN
       CAST(split_part(s, '/', 1) AS double_precision) 
       / CAST(split_part(s, '/', 2) AS double_precision)
   ELSE
       CAST(s AS DOUBLE PRECISION)
   END CASE
END

Then you can ORDER BY fraction_to_number(weird_column)

If possible, I would revisit the data design. Is it all this complexity really necessary?