Looking at the fastest way to convert a field in a table and wonder if in
general an update with a CASE WHEN construction or an update with a join to
a lookup table is faster.
These conversions are of this type:
UPDATE A3SQL77D_J
SET ENTRY_TYPE = (case
when ENTRY_TYPE = 9 then 'Issue
when ENTRY_TYPE = 2 then 'Note'
when ENTRY_TYPE = 1 then 'Encounter'
when ENTRY_TYPE = 8 then 'Authorisation'
when ENTRY_TYPE = 11 then 'Prescription'
when ENTRY_TYPE = 5 then 'Treatment'
when ENTRY_TYPE = 3 then 'Problem'
when ENTRY_TYPE = 13 then 'Discontinuation'
when ENTRY_TYPE = 6 then 'Reminder'
when ENTRY_TYPE = 14 then 'Adverse reaction'
when ENTRY_TYPE = -1 then 'Unknown'
when ENTRY_TYPE = 4 then 'Sub-problem'
when ENTRY_TYPE = 7 then 'Battery'
when ENTRY_TYPE = 10 then 'Return-Script'
else ENTRY_TYPE end)
So, an integer value to be converted to a limited number of strings.
I could figure this out with some testing, but maybe there are some general
rules that apply to this.
Also, would the order of the CASE WHEN options make a difference,
speed-wise, so would it be faster to have the WHEN options in decreasing
order of frequency?
RBS
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