Shantanu's Blog

Corporate Consultant

September 12, 2015

 

Redshift support of User Defined functions

The following example creates a function that compares two numbers and returns the larger value. Note that the indentation of the code between the double dollar signs ($$) is a Python requirement.

create function f_greater(a float, b float)
returns float
stable
as $$
  if a > b:
    return a
  return b
$$ language plpythonu;

The following query calls the new f_greater function to query the SALES table and return either COMMISSION or 20 percent of PRICEPAID, whichever is greater:
select f_greater(commission, pricepaid*0.20) from sales;

# Z-score calculation

create function f_z_test_by_pval (alpha float, x_bar float, test_val float, sigma float, n float)
RETURNS varchar
STABLE
AS $$

 import scipy.stats as st
 import math as math

 z = (x_bar - test_val) / (sigma / math.sqrt(n))

 p = st.norm.cdf(z)

 if p <= alpha:
   return 'Statistically significant'

 else:
   return 'May have occurred by random chance'

$$LANGUAGE plpythonu;

# string function

create function
f_return_focused_specialty(full_physician_specialty varchar)
RETURNS varchar
STABLE
AS $$

    parts = full_physician_specialty.split("/")
    return parts[len(parts) - 1].strip()

$$LANGUAGE plpythonu

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