Replacing Placeholder values with another table's data - sql

Question

I have 2 tables .The first table contains rows with placeholders and the second table contains those placeholders values.
I want a query which fetches data from the first table and replaces placeholders with actual values which are stored in the second table.
Ex:
Table1 Data
id value
608CB424-90BF-4B08-8CF8-241C7635434F jdbc:postgresql://{POSTGRESIP}:{POSTGRESPORT}/{TESTDB}
CDA4C3D4-72B5-4422-8071-A29D32BD14E0 https://{SERVICEIP}/svc/{TESTSERVICE}/
Table2 Data
id placeolder value
201FEBFE-DF92-4474-A945-A592D046CA02 POSTGRESIP 1.2.3.4
20D9DE14-643F-4CE3-B7BF-4B7E01963366 POSTGRESPORT 5432
45611605-F2D9-40C8-8C0C-251E300E183C TESTDB mytest
FA8E2E4E-014C-4C1C-907E-64BAE6854D72 SERVICEIP 10.90.30.40
45B76C68-8A0F-4FD3-882F-CA579EC799A6 TESTSERVICE mytest-service
Required output is
id value
608CB424-90BF-4B08-8CF8-241C7635434F jdbc:postgresql://1.2.3.4:5432/mytest
CDA4C3D4-72B5-4422-8071-A29D32BD14E0 https://10.90.30.40/svc/mytest-service/

Answer 1

If you want to use Python-like named placeholders then you need the helper function written on plpythonu:
create extension plpythonu;
create or replace function formatpystring( str text, a json ) returns text immutable language plpythonu as $$
import json
d = json.loads(a)
return str.format(**d)
$$;
Then simple test:
select formatpystring('{foo}.{bar}', '{"foo": "win", "bar": "amp"}');
formatpystring
----------------
win.amp
Finally you need to compose those arguments from your tables. It is simple:
select t1.id, formatpystring(t1.value, json_object_agg(t2.placeholder, t2.value)) as value
from table1 as t1, table2 as t2
group by t1.id, t1.value;
(Query was not tested but you have the direction)

Answer 2

(Clumsy) dynamic SQL implementation, featuring an outer join, but generating a recursive function call:
This function will not be very efficient, but probably the translation table is relatively small.
CREATE TABLE xlat_table (aa text ,bb text);
INSERT INTO xlat_table (aa ,bb ) VALUES( 'BBB', '/1.2.3.4/')
,( 'ccc', 'OMG') ,( 'ddd', '/4.3.2.1/') ;
CREATE FUNCTION dothe_replacements(_arg1 text) RETURNS text
AS
$func$
DECLARE
script text;
braced text;
res text;
found record; -- (aa text, bb text, xx text);
BEGIN
script := '';
res := format('%L', _arg1);
for found IN SELECT xy.aa,xy.bb
, regexp_matches(_arg1, '{\w+}','g' ) AS xx
FROM xlat_table xy
LOOP
-- RAISE NOTICE '#xx=%', found.xx[1];
-- RAISE NOTICE 'aa=%', found.aa;
-- RAISE NOTICE 'bb=%', found.bb;
braced := '{'|| found.aa || '}';
IF (found.xx[1] = braced ) THEN
-- RAISE NOTICE 'Res=%', res;
script := format ('replace(%s, %L, %L)'
,res,braced,found.bb);
res := format('%s', script);
END IF;
END LOOP;
if(length(script) =0) THEN return res; END IF;
script :='Select '|| script;
-- RAISE NOTICE 'script=%', script;
EXECUTE script INTO res;
return res;
END;
$func$
LANGUAGE plpgsql;
SELECT dothe_replacements( 'aaa{BBB}ccc{ddd}eee' );
SELECT dothe_replacements( '{AAA}bbb{CCC}DDD}{EEE}' );
Results:
CREATE TABLE
INSERT 0 3
CREATE FUNCTION
dothe_replacements
-----------------------------
aaa/1.2.3.4/ccc/4.3.2.1/eee
(1 row)
dothe_replacements
--------------------------
'{AAA}bbb{CCC}DDD}{EEE}'
(1 row)
The above method has quadratic behaviour(wrt the numberof xlat-entries); which is horrible.
But,we could dynamically create a function (once) and call it multiple times
(a poor man's generator)
Selecting only the relevant entries from the xlat table should probably be added.
And, you should of course re-create the function everytime the xlat table is changed.
CREATE FUNCTION create_replacement_function(_name text) RETURNS void
AS
$func$
DECLARE
argname text;
res text;
script text;
braced text;
found record; -- (aa text, bb text, xx text);
BEGIN
script := '';
argname := '_arg1';
res :=format('%I', argname);
for found IN SELECT xy.aa,xy.bb
FROM xlat_table xy
LOOP
-- RAISE NOTICE 'aa=%', found.aa;
-- RAISE NOTICE 'bb=%', found.bb;
-- RAISE NOTICE 'Res=%', res;
braced := '{'|| found.aa || '}';
script := format ('replace(%s, %L, %L)'
,res,braced,found.bb);
res := format('%s', script);
END LOOP;
script :=FORMAT('CREATE FUNCTION %I (_arg1 text) RETURNS text AS
$omg$
BEGIN
RETURN %s;
END;
$omg$ LANGUAGE plpgsql;', _name, script);
RAISE NOTICE 'script=%', script;
EXECUTE script ;
return ;
END;
$func$
LANGUAGE plpgsql;
SELECT create_replacement_function( 'my_function');
SELECT my_function('aaa{BBB}ccc{ddd}eee' );
SELECT my_function( '{AAA}bbb{CCC}DDD}{EEE}' );
And the result:
CREATE FUNCTION
NOTICE: script=CREATE FUNCTION my_function (_arg1 text) RETURNS text AS
$omg$
BEGIN
RETURN replace(replace(replace(_arg1, '{BBB}', '/1.2.3.4/'), '{ccc}', 'OMG'), '{ddd}', '/4.3.2.1/');
END;
$omg$ LANGUAGE plpgsql;
create_replacement_function
-----------------------------
(1 row)
my_function
-----------------------------
aaa/1.2.3.4/ccc/4.3.2.1/eee
(1 row)
my_function
------------------------
{AAA}bbb{CCC}DDD}{EEE}
(1 row)

Answer 3

The following offers a plpgsql solution in a with a single function.
You'll notice I've 'renamed' the value column. It's bad practice using rserved/key words as object names. Also soq is the schema I use for all SO code.
The process first takes the holder-values from table2 and generates a set of key-value pairs (in this case hstore, but jsonb would also work). It then builds an array from the value column (my column name: val_string) containing the place_holder name from the value. Finally, it iterates that array replacing the actual holder-name with the value from the key-values using the array value as the lookup key.
The performance would not be great with a larger volume from either table. If you need to process a large volume at a time to a single row temp table may yield better performance.
create or replace function soq.replace_holders( place_holder_line_in text)
returns text
language plpgsql
as $$
declare
l_holder_values hstore;
l_holder_line text;
l_holder_array text[];
l_indx integer;
begin
-- transform cloumns to key-value pairs of holder-value
select string_agg(place,',')::hstore
into l_holder_values
from (
select concat( '"',place_holder,'"=>"',place_value,'"') place
from soq.table2
) p;
-- raise notice 'holder_array_in==%',l_holder_values;
-- extract the text line and build array of place_holder names
select phv, string_to_array (string_agg(v,','),',')
into l_holder_line,l_holder_array
from (
select replace(replace(place_holder_line_in,'{',''),'}','') phv
, replace(replace(replace(regexp_matches(place_holder_line_in,'({[^}]+})','g')::text ,'{',''),'}',''),'"','') v
) s
group by phv;
-- raise notice 'Array==%',l_holder_array::text;
-- replace each key from text line with the corresponding value
for l_indx in 1 .. array_length(l_holder_array,1)
loop
l_holder_line = replace(l_holder_line,l_holder_array[l_indx],l_holder_values -> l_holder_array[l_indx]);
end loop;
-- done
return l_holder_line;
end;
$$;
-- Test driver
select id, soq.replace_holders(val_string) result_value from soq.table1;

Answer 4

I have created a simple query for this solution and it working as required.
WITH RECURSIVE cte(id, value, level) AS (
SELECT id,value, 0 as level
FROM Table1
UNION
SELECT ts.id,replace(ts.value,'{'||tp.placeholder||'}',tp.value) as value, level+1
FROM cte ts, Table2 tp WHERE ts.value LIKE CONCAT('%',tp.placeholder, '%')
)
SELECT id, value FROM cte c
where level =
(
select Max(level)
from cte c2 where c.id=c2.id
)
Output is
id value
CDA4C3D4-72B5-4422-8071-A29D32BD14E0 https://10.90.30.40/svc/mytest-service/
608CB424-90BF-4B08-8CF8-241C7635434F jdbc:postgresql://1.2.3.4:5432/mytest