create missing sequence for database tables containing column called id - postgresql

Question

i'm trying to fix database issue related to creating missing sequence of the table after moving database from lower to higher version but i face 2 issues
first here is what i tried so far:
DO $$
DECLARE
i TEXT;
BEGIN
FOR i IN (select table_name from information_schema.tables where table_catalog='cst_sh' and table_schema='public') LOOP
IF EXISTS (SELECT count(*) FROM information_schema.columns WHERE table_name=table_name and column_name='id') THEN
EXECUTE 'CREATE SEQUENCE IF NOT EXISTS '''||i||'_id_seq''';
EXECUTE 'Select setval('''||i||'_id_seq'', (SELECT max(id) as a FROM ' || i ||')+1,true);';
end if;
END LOOP;
END$$;
1st problem is that the condition doesn't seem to work. First i check if the table has column called id then i start to create the sequence if exist and then set the value for it but some tables doesn't have id column so the second query fail.
2nd problem is with the 1st query that i use to create the sequence if it doesn't exist, it fails every time and i dont know why
the error is :
QUERY: CREATE SEQUENCE IF NOT EXISTS 'xxxx'
CONTEXT: PL/pgSQL function inline_code_block line 7 at EXECUTE

Answer 1

You should only loop over tables that actually have such a column. This can be achieved by using an EXISTS condition.
select t.table_name, t.table_schema
from information_schema.tables t
where t.table_schema = 'public'
and exists (select *
from information_schema.columns c
where t.table_name = c.table_name
and t.table_schema = c.table_schema
and c.column_name = 'id')
To create a safe SELECT statement you need to include the schema name of the table when getting the max() value.
Dynamic SQL is a lot easier to write if you use format() instead of string concatenation. You create a statement create sequence 'foo_id_seq' putting the sequence name in single quotes - but that's invalid for identifiers.
When you loop over a SELECT statement the loop variable should be a record, not a text value.
So putting that all together your code should look something like this:
DO $$
DECLARE
l_rec record;
l_seq_name text;
BEGIN
FOR l_rec IN select t.table_name, t.table_schema
from information_schema.tables t
where t.table_schema = 'stuff'
and exists (select *
from information_schema.columns c
where t.table_name = c.table_name
and t.table_schema = c.table_schema
and c.column_name = 'id')
LOOP
l_seq_name := l_rec.table_name||'_id_seq';
EXECUTE format('CREATE SEQUENCE IF NOT EXISTS %I', l_seq_name);
EXECUTE format('select setval(%L, max(id)) FROM %I.%I', l_seq_name, l_rec.table_schema, l_rec.table_name);
END LOOP;
END
$$;
You probably also want to make the sequence owned by the column, so you should add:
EXECUTE format('alter sequence %I owned by %I.%I.id', l_seq_name, l_rec.table_schema, l_rec.table_name);