PostgreSQL - How to change Length of Different Tables Columns with Cursors - postgresql

Question

I'm changing column lengths for all necessary tables but I got some errors.
I am using PostgreSQL 10 and pgAdmin4 but I couldn't see error messages.
I guess, because of the pgAdmin version. Firstly, I couldn't declare CURSOR, I don't know why? I had succeeded on Oracle.
Can you help me about this situation? My code as shown below;
do $$
DECLARE
modify_column_cursor CURSOR FOR
SELECT 'ALTER TABLE "schema_name"."' || C.TABLE_NAME || '" ALTER COLUMN'|| C.COLUMN_NAME||' varchar(128)' as alter_sql, TABLE_NAME t_name, COLUMN_NAME c_name, 128 c_length FROM information_schema.columns c WHERE column_name LIKE '%PROD_NUM' and TABLE_NAME not like '%STAGING%' UNION
SELECT 'ALTER TABLE "schema_name"."' || C.TABLE_NAME || '" ALTER COLUMN'|| C.COLUMN_NAME||' varchar(128)' as alter_sql, TABLE_NAME t_name, COLUMN_NAME c_name, 128 c_length FROM information_schema.columns c WHERE column_name LIKE '%PREV_PROD_NUM' and TABLE_NAME not like '%STAGING%';
--.
--.
--.
sql_stmt VARCHAR(800);
c_length numeric;
c_length_db numeric;
flag numeric := 0;
BEGIN
--OPEN modify_column_cursor;
for modify_column in modify_column_cursor LOOP
raise notice 'asd : %', modify_column.ex_name;
sql_stmt := 'SELECT character_maximum_length FROM information_schema.columns WHERE column_name = ''' || modify_column.c_name || ''' and table_name = ''' || modify_column.t_name || ''' and table_schema = ''schema_name''';
EXECUTE sql_stmt INTO c_length_db;
IF c_length_db > modify_column.c_length THEN
sql_stmt := 'select max(length(' || modify_column.c_name || ')) from "schema_name".' || modify_column.t_name;
EXECUTE sql_stmt INTO c_length;
IF c_length > modify_column.c_length THEN
flag := 1;
raise notice '--------------INCONSISTENED FIELD FOUND---------------';
raise notice '% - % - % Not Ok! Default field size in db: %', modify_column.t_name, modify_column.c_name, modify_column.c_length, c_length_db;
raise notice '% - % - % Not Ok! Field has a data with length: %', modify_column.t_name, modify_column.c_name, modify_column.c_length, c_length;
raise notice '-------------------------------------------------------';
raise notice ' ';
ELSE
NULL;
END IF;
ELSE
NULL;
END IF;
END LOOP;
IF flag = 0 THEN
FOR modify_column IN modify_column_cursor
LOOP
EXECUTE modify_column.alter_sql;
END LOOP;
raise notice ' ';
raise notice '-----FIELDS ARE SUCCESSFULLY MODIFIED-----';
ELSE
raise notice ' ';
raise notice '-----ERROR: SOME FIELDS ARE NOT SUITABLE TO ALTER-----';
END IF;
end$$;

Answer 1

I am on PostgreSQL 11 but if I remember well its pretty much the same.
If you want to absolutely use a loop to do that I corrected a little your code and injected a debug table.
You had a missing blank space and a wrong declaration of the cursor. I simply got ride of it.
You can read this excellent article on cursor on postgresql if you want : http://www.postgresqltutorial.com/plpgsql-cursor/
do $$
DECLARE
sql_stmt VARCHAR(800);
c_length numeric;
c_length_db numeric;
flag numeric := 0;
modify_column record;
begin
create table if not exists [your_schema_name].test (query varchar);
for modify_column in
SELECT 'ALTER TABLE "'||[your_schema_name]||'"."' || C.TABLE_NAME || '" ALTER COLUMN '|| C.COLUMN_NAME||' varchar(128)' as alter_sql
, TABLE_NAME t_name
, COLUMN_NAME c_name
, 128 c_length
FROM information_schema.columns c
where table_schema = ''||[your_schema_name]||''
LOOP
--raise notice 'asd : %', modify_column.ex_name;
sql_stmt := 'SELECT character_maximum_length FROM information_schema.columns WHERE column_name = ''' || modify_column.c_name || ''' and table_name = ''' || modify_column.t_name || ''' and table_schema = '''||[your_schema_name]||'''';
insert into [your_schema_name].test values (sql_stmt);
EXECUTE sql_stmt INTO c_length_db;
IF c_length_db > modify_column.c_length THEN
sql_stmt := 'select max(length(' || modify_column.c_name || ')) from "'||[your_schema_name]||'".' || modify_column.t_name;
--EXECUTE sql_stmt INTO c_length;
insert into [your_schema_name].test values (sql_stmt);
IF c_length > modify_column.c_length THEN
flag := 1;
raise notice '--------------INCONSISTENED FIELD FOUND---------------';
raise notice '% - % - % Not Ok! Default field size in db: %', modify_column.t_name, modify_column.c_name, modify_column.c_length, c_length_db;
raise notice '% - % - % Not Ok! Field has a data with length: %', modify_column.t_name, modify_column.c_name, modify_column.c_length, c_length;
raise notice '-------------------------------------------------------';
raise notice ' ';
ELSE
NULL;
END IF;
ELSE
NULL;
END IF;
END LOOP;
IF flag = 0 THEN
--FOR modify_column IN modify_column_cursor
-- LOOP
-- EXECUTE modify_column.alter_sql;
--END LOOP;
raise notice ' ';
raise notice '-----FIELDS ARE SUCCESSFULLY MODIFIED-----';
ELSE
raise notice ' ';
raise notice '-----ERROR: SOME FIELDS ARE NOT SUITABLE TO ALTER-----';
END IF;
end;
$$;