i have a variable that is a name of a table. How can i select or update from this using variable in query , for example:
create or replace function pg_temp.testtst ()
returns varchar(255) as
$$
declare
r record; t_name name;
begin
for r in SELECT tablename FROM pg_tables WHERE schemaname = 'public' limit 100 loop
t_name = r.tablename;
update t_name set id = 10 where id = 15;
end loop;
return seq_name;
end;
$$
language plpgsql;
it shows
ERROR: relation "t_name" does not exist
Correct reply is a comment from Anton Kovalenko
You cannot use variable as table or column name in embedded SQL ever.
UPDATE dynamic_table_name SET ....
PostgreSQL uses a prepared and saved plans for embedded SQL, and references to a target objects (tables) are deep and hard encoded in plans - a some characteristics has significant impact on plans - for one table can be used index, for other not. Query planning is relatively slow, so PostgreSQL doesn't try it transparently (without few exceptions).
You should to use a dynamic SQL - a one purpose is using for similar situations. You generate a new SQL string always and plans are not saved
DO $$
DECLARE r record;
BEGIN
FOR r IN SELECT table_name
FROM information_schema.tables
WHERE table_catalog = 'public'
LOOP
EXECUTE format('UPDATE %I SET id = 10 WHERE id = 15', r.table_name);
END LOOP;
END $$;
Attention: Dynamic SQL is unsafe (there is a SQL injection risks) without parameter sanitization. I used a function "format" for it. Other way is using "quote_ident" function.
EXECUTE 'UPDATE ' || quote_ident(r.table_name) || 'SET ...
Related
I have function which supposed to create missing objects. I have a variable that I am using to set active schema tschem_name
However feels like proc cannot see this variable if it is trying to create this object, however, if which check if object exists can see this variable feels like it treats it as a column from the table. Any idea how to work around it? I was trying to use declare inside else statement but it doesn't work :(
ERROR: column "tschem_name" does not exist
CREATE OR REPLACE FUNCTION public.fn_upd_schema(
tschem_name character varying
)
RETURNS character varying
LANGUAGE 'plpgsql'
COST 100
VOLATILE PARALLEL UNSAFE
AS $BODY$
DECLARE
--tname text := t_shema;
--tschem_name text := tname||'_assets';
tsql_dyn text ;
nschema_check numeric := 0 ;
BEGIN
SELECT 1
INTO nschema_check
FROM PG_NAMESPACE
WHERE NSPNAME = tschem_name;
IF nschema_check = 0 THEN
RETURN 'Schema '||tschem_name ||' Does Not Exist';
ELSE
tsql_dyn := 'SET search_path TO '||tschem_name ||';';
raise notice 'EXECUTE %', tsql_dyn;
EXECUTE tsql_dyn;
IF EXISTS (SELECT FROM information_schema.tables
WHERE table_schema = tschem_name
AND table_type = 'VIEW'
AND table_name = 'vw_aaa')
THEN
null;-- raise notice 'vw_aaa EXISTS';
ELSE
--declare tschemaname text := tschem_name;
CREATE VIEW vw_aaa AS
SELECT
tschem_name::text AS database,
tale1.column1,
tale1.column2
From table1;
endif;
RETURN tschem_name ||' UPDATED TO STANDART';
END IF;
END;
$BODY$;
The problem is your CREATE VIEW statement. You need to use dynamic SQL with EXECUTE for that.
The underlying reason is that CREATE VIEW does not accept parameters.
By the way, your code is vulnerable to SQL injection. Never construct an SQL statement by concatenating strings with ||. Use format with the %I placeholder.
I'm trying to create a function on PostgreSQL, and I have some problem to use a local variable. Here's my code :
DECLARE query RECORD;
DECLARE schema_name TEXT;
BEGIN
FOR query IN SELECT * FROM context WHERE created_at + make_interval(days => duration) <= CURRENT_TIMESTAMP LOOP
SELECT lower(quote_ident(query.title)) INTO schema_name;
DROP SCHEMA schema_name CASCADE;
DELETE FROM context WHERE id = query.id;
END LOOP;
RETURN 1;
END;
$$ LANGUAGE plpgsql;
The select and delete queries work fine, and I've made a test returning the value of schema_name variable, and it's OK.
My problem is with this line :
DROP SCHEMA schema_name CASCADE;
I get an error as "the schema 'schema_name' doesn't exist".
I'd really appreciate any ideas for how to use this variable to do the drop query.
You need dynamic SQL for this:
DECLARE
query RECORD;
BEGIN
FOR query IN SELECT id, lower(title) as title
FROM context
WHERE created_at + make_interval(days => duration) <= CURRENT_TIMESTAMP
LOOP
execute format('DROP SCHEMA %I CASCADE', query.title);
DELETE FROM context WHERE id = query.id;
END LOOP;
RETURN 1;
END;
$$ LANGUAGE plpgsql;
I also removed the unnecessary SELECT statement to make the title lower case, this is better done in the query directly.
Also: variable assignment is faster with := then with select, so:
schema_name := lower(quote_ident(query.title));
would be better if the variable was needed.
I'm new to plpgsql. I'm trying to run a simple query in plpgsql using a variable as table name in plpgsql. But the variable is being interpreted as the table name instead of the value of the variable being interpreted as variable name.
DECLARE
v_table text;
z_table text;
max_id bigint;
BEGIN
FOR v_table IN
SELECT table_name
FROM information_schema.tables
WHERE table_catalog = 'my_database'
AND table_schema = 'public'
AND table_name not like 'z_%'
LOOP
z_table := 'z_' || v_table;
SELECT max(id) from z_table INTO max_id;
DELETE FROM v_table where id > max_id;
END LOOP;
Some background information. For every table in my database, I have another table starting with "z_". E.g. for a table called "employee" I have identical table called "z_employee". z_employee contains the same set of data as employee. I use it to restore the employee table at the start of every test.
When I run this function I get the following error:
ERROR: relation "z_table" does not exist
LINE 1: SELECT max(id) from z_table
My guess is that I'm not allowed to use the variable z_table in the SQL query. At least not the way I'm using it here. But I don't know how it's supposed to be done.
Use dynamic SQL with EXECUTE, simplify, and escape identifiers properly:
CREATE OR REPLACE FUNCTION f_test()
RETURNS void AS
$func$
DECLARE
v_table text;
BEGIN
FOR v_table IN
SELECT table_name
FROM information_schema.tables
WHERE table_catalog = 'my_database'
AND table_schema = 'public'
AND table_name NOT LIKE 'z_%'
LOOP
EXECUTE format('DELETE FROM %I v WHERE v.id > (SELECT max(id) FROM %I)'
, v_table, 'z_' || v_table);
END LOOP;
END
$func$ LANGUAGE plpgsql;
Table names may need to be quoted to defend against syntax errors or even SQL injection! I use the convenient format() to concatenate the DELETE statement and escape identifiers properly.
A separate SELECT would be more expensive. You can do it all with a single DELETE statement.
Related:
Table name as a PostgreSQL function parameter
Aside:
You might use the (slightly faster) system catalog pg_tables instead:
SELECT tablename
FROM pg_catalog.pg_tables
WHERE schemaname = 'public'
AND tablename NOT LIKE 'z_%'
See:
How to check if a table exists in a given schema
table_catalog in information_schema.tables has no equivalent here. Only tables of the current database are visible anyway. So the above predicate WHERE table_catalog = 'my_database' produces an empty result set when connected to the wrong database.
I am trying to have a dynamic variable that I can specify different column's with (depending on some if statements). Explained in code, I am trying to replace this:
IF (TG_TABLE_NAME='this') THEN INSERT INTO table1 (name_id) VALUES id.NEW END IF;
IF (TG_TABLE_NAME='that') THEN INSERT INTO table1 (lastname_id) VALUES id.NEW END IF;
IF (TG_TABLE_NAME='another') THEN INSERT INTO table1 (age_id) VALUES id.NEW END IF;
With this:
DECLARE
varName COLUMN;
BEGIN
IF (TG_TABLE_NAME='this') THEN varName = 'name_id';
ELSE IF (TG_TABLE_NAME='that') THEN varName = 'lastname_id';
ELSE (TG_TABLE_NAME='another') THEN varName = 'age_id';
END IF;
INSERT INTO table1 (varName) VALUES id.NEW;
END;
The INSERT string is just an example, it's actually something longer. I am a beginner at pgSQL. I've seen some examples but I'm only getting more confused. If you can provide an answer that is also more safe from SQL injection that would be awesome.
One way to do what you're looking for is to compose your INSERT statement dynamically based on the named table. The following function approximates the logic you laid out in the question:
CREATE OR REPLACE FUNCTION smart_insert(table_name TEXT) RETURNS VOID AS $$
DECLARE
target TEXT;
statement TEXT;
BEGIN
CASE table_name
WHEN 'this' THEN target := 'name_id';
WHEN 'that' THEN target := 'lastname_id';
WHEN 'another' THEN target := 'age_id';
END CASE;
statement :=
'INSERT INTO '||table_name||'('||target||') VALUES (nextval(''id''));';
EXECUTE statement;
END;
$$ LANGUAGE plpgsql;
Note that I'm using a sequence to populate these tables (the call to nextval). I'm not sure if that is your use case, but hopefully this example is extensible enough for you to modify it to fit your scenario. A contrived demo:
postgres=# SELECT smart_insert('this');
smart_insert
--------------
(1 row)
postgres=# SELECT smart_insert('that');
smart_insert
--------------
(1 row)
postgres=# SELECT name_id FROM this;
name_id
---------
101
(1 row)
postgres=# SELECT lastname_id FROM that;
lastname_id
-------------
102
(1 row)
Your example doesn't make a lot of sense. Probably over-simplified. Anyway, here is a trigger function for the requested functionality that inserts the new id in a selected column of a target table, depending on the triggering table:
CREATE OR REPLACE FUNCTION smart_insert(table_name TEXT)
RETURNS trigger AS
$func$
BEGIN
EXECUTE
'INSERT INTO table1 ('
|| CASE TG_TABLE_NAME
WHEN 'this' THEN 'name_id'
WHEN 'that' THEN 'lastname_id'
WHEN 'another' THEN 'age_id'
END CASE
||') VALUES ($1)'
USING NEW.id;
END
$func$ LANGUAGE plpgsql;
To refer to the id column of the new row, use NEW.id not id.NEW.
To pass a value to dynamic code, use the USING clause of EXECUTE. This is faster and more elegant, avoids casting to text and back and also makes SQL injection impossible.
Don't use many variables and assignments in plpgsql, where this is comparatively expensive.
If the listed columns of the target table don't have non-default column defaults, you don't even need dynamic SQL:
CREATE OR REPLACE FUNCTION smart_insert(table_name TEXT)
RETURNS trigger AS
$func$
BEGIN
INSERT INTO table1 (name_id, lastname_id, age_id)
SELECT CASE WHEN TG_TABLE_NAME = 'this' THEN NEW.id END
, CASE WHEN TG_TABLE_NAME = 'that' THEN NEW.id END
, CASE WHEN TG_TABLE_NAME = 'another' THEN NEW.id END;
END
$func$ LANGUAGE plpgsql;
A CASE expression without ELSE clause defaults to NULL, which is the default column default.
Both variants are safe against SQL injection.
I'm trying to load some data from CSV using the postgresql COPY command. The trick is that I'd like to implement multi-tenancy on a userid (which is contained in the CSV). Is there an easy way to tell the postgres copy command to filter based on this userid when loading the csv?
i.e. all rows with userid=x go to schema=x, rows with userid=y go to schema=y.
There is not a way of doing this with just the COPY command, but you could copy all your data into a master table, and then put together a simple PL/PGSQL function that does this for you. Something like this -
CREATE OR REPLACE FUNCTION public.spike()
RETURNS void AS
$BODY$
DECLARE
user_id integer;
destination_schema text;
BEGIN
FOR user_id IN SELECT userid FROM master_table GROUP BY userid LOOP
CASE user_id
WHEN 1 THEN
destination_schema := 'foo';
WHEN 2 THEN
destination_schema := 'bar';
ELSE
destination_schema := 'baz';
END CASE;
EXECUTE 'INSERT INTO '|| destination_schema ||'.my_table SELECT * FROM master_table WHERE userid=$1' USING user_id;
-- EXECUTE 'DELETE FROM master_table WHERE userid=$1' USING user_id;
END LOOP;
TRUNCATE TABLE master_table;
RETURN;
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE
COST 100;
This gets all unique user_ids from the master_table, uses a CASE statement to determine the destination schema, and then executes an INSERT SELECT to move rows, and finally deletes the moved rows.