pl/pgsql: How show values of NEW & OLD trigger record if i don't know the name of original table colum? - sql

Question

Hi all,
I wrote a function in pl/pgsql and I have this problem:
I want use the values of NEW and OLD trigger record but I don't know the column name and number if the table.
for example:
CREATE OR REPLACE FUNCTION tt() RETURNS trigger AS $$
DECLARE
text1 text;
text2 text;
orig_name text =tg_argv[0];
orig_schema text =tg_argv[1];
log_name text =tg_argv[2];
log_schema text =tg_argv[3];
col pg_attribute.attname%TYPE;
[...]
BEGIN
orig_comp := quote_ident(orig_schema)||'.'||quote_ident(orig_name);
log_comp := quote_ident(log_schema)||'.'||quote_ident(log_name);
IF(trigger_mode='INSERT')
THEN
-- I want know the names of column
FOR colonna in
SELECT attname
FROM pg_attribute
WHERE attrelid = orig_comp::regclass
AND attnum > 0
AND NOT attisdropped
loop --for each column I want save the value like a string
text1=NEW||'.'||colonna; -- this don't work: error: record NEW don't have colonna like values
text2:=text2||' , '||text1;
end loop;
[...]
END IF;
[...]
RETURN NEW;
END;
$$ LANGUAGE plpgsql;

Answer 1

you know a original name - it is a variable TG_TABLE_NAME. And dynamic access to record fields is possible with EXECUTE USING statement.
CREATE OR REPLACE FUNCTION dynamic_trigger()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
DECLARE
ri RECORD;
t TEXT;
BEGIN
RAISE NOTICE E'\n Operation: %\n Schema: %\n Table: %',
TG_OP,
TG_TABLE_SCHEMA,
TG_TABLE_NAME;
FOR ri IN
SELECT ordinal_position, column_name, data_type
FROM information_schema.columns
WHERE
table_schema = quote_ident(TG_TABLE_SCHEMA)
AND table_name = quote_ident(TG_TABLE_NAME)
ORDER BY ordinal_position
LOOP
EXECUTE 'SELECT ($1).' || ri.column_name || '::text' INTO t USING NEW;
RAISE NOTICE E'Column\n number: %\n name: %\n type: %\n value: %.',
ri.ordinal_position,
ri.column_name,
ri.data_type,
t;
END LOOP;
RETURN NEW;
END; $$;
This code is wrote by Tom Lane and it is from postgresql tricks pages Iteration over RECORD variable inside trigger.