Question

Postgresql 9.2 DB which automatically collects data from various machines.
The DB stores all the data including the machine id, the firmware, the manufacturer id etc as well as the actual result data. In one stored field (varchar) there are 5 sub fields which are separated by the ^ character.

ACT18!!!8246-EN-2.00013151!1^7.00^F5260046959^H1P1O1R1C1Q1L1^1 (Machine 1)

The order of this data seems to vary from one machine to another. Eg machine 1 2 and 3. The string above shows the firmware version, in this case “7.0” and it appears in sub-field 2. However, another machine sends the data in a different sub-field – in this case sub-field 3 and the value is “1”

BACT/ALERT^A.00^1^^ (Machine 2)

I want to store the values “7.0” and “1” in a different field in a separate table using a CREATE TRIGGER t_machine_id AFTER INSERT function where I can choose which sub-field is used depending on the machine the data has come from.

Is split_part the best function to do this? Can anyone supply an example code that will do this? I can’t find anything in the documentation.

Answer 1

You need to (a) split the data using something like regexp_split_to_table then (b) match which parts are which using some criteria, since you don’t have field position-order to rely on. Right now I don’t see any reliable rule to decide what’s the firmware version and what’s the machine number; you can’t really say where field <> machine_number because if machine 1 had firmware version 1 you’d get no results.

Given dummy data:

CREATE TABLE machine_info(data text, machine_no integer);
INSERT INTO machine_info(data,machine_no) (VALUES
  ('ACT18!!!8246-EN-2.00013151!1^7.00^F5260046959^H1P1O1R1C1Q1L1^1',1),
  ('BACT/ALERT^A.00^1^^',2)
);

Something like:

SELECT machine_no, regexp_split_to_table(data,'\^') 
FROM machine_info;

will give you a table of split data elements with machine number, but then you need to decide which fields are which:

 machine_no |    regexp_split_to_table     
------------+------------------------------
          1 | ACT18!!!8246-EN-2.00013151!1
          1 | 7.00
          1 | F5260046959
          1 | H1P1O1R1C1Q1L1
          1 | 1
          2 | BACT/ALERT
          2 | A.00
          2 | 1
          2 | 
          2 | 
(10 rows)

You may find the output of substituting regexp_split_to_array more useful, depending on whether you can get any useful info from field order and how you intend to process the data.

regress=# SELECT machine_no, regexp_split_to_array(data,'\^') 
          FROM machine_info;
 machine_no |                      regexp_split_to_array                       
------------+------------------------------------------------------------------
          1 | {ACT18!!!8246-EN-2.00013151!1,7.00,F5260046959,H1P1O1R1C1Q1L1,1}
          2 | {BACT/ALERT,A.00,1,"",""}
(2 rows)

Say there are two firmware versions; version 1 sends code^blah^fwvers^^ and version 2 and higher sends code^fwvers^blah^blah2^machineno. You can then differentiate between the two because you know that version 1 leaves the last two fields blank:

SELECT
  machine_no,
  CASE WHEN info_arr[4:5] = ARRAY['',''] THEN info_arr[3] ELSE info_arr[2] END AS fw_vers
FROM (
  SELECT machine_no, regexp_split_to_array(data,'\^')
  FROM machine_info
) string_parts(machine_no, info_arr);

results:

 machine_no | fw_vers 
------------+---------
          1 | 7.00
          2 | 1
(2 rows)

Of course, you’ve only provided two sample data, so the real matching rules are likely to be more complex. Consider writing an SQL function to extract the desired field(s) and return them from the array passed.