After some answer on a previous question (request over several schema), I try to write a stored procedure to select tables for several schemas (Each user have a schema).
create or replace public.select_simulations() returns setof simulation as $$
declare
users pg_user%ROWTYPE;
simu simulation%ROWTYPE;
begin
for users in select usename from pg_user where usename <> 'postgres' loop
for simu in select id, name from (users.usename).simulation loop
return next simu;
end loop;
end loop;
end;
$$
but it doesn't accept the (users.usename).simulation, and without the parenthesis it produced an error (seems to search a sub field, not a schema)...
So what is the correct syntax to tell that users.usename is a schema name ?
Thank you for your help!
You could take a look at the for-in-execute control structure:
FOR record_or_row IN EXECUTE text_expression LOOP
statements
END LOOP [ label ];
http://www.postgresql.org/docs/8.1/static/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING
Something like:
...
for users in select usename from pg_user where usename <> 'postgres' loop
for simu in execute 'select id, name from '||quote_ident(users.usename)||'.simulation' loop
return next simu;
end loop;
end loop;
...
Related
I'm migrating an Oracle PLSQL SP to be compatible with Postgres plpgsql (version PostgreSQL 13.6 on x86_64-pc-linux-gnu, compiled by x86_64-pc-linux-gnu-gcc (GCC) 7.4.0, 64-bit).
The exception block of the PLSQL SP has the below code:
exception
when others then
if CURR1%isopen then
close SPV_RECON_INFO;
end if;
open CURR1 for execute select sysdate from dual;
END;
How can %isopen be implemented in Postgres?
That is simple. You have to assign a name to the cursor variable, then you can search for that cursor in pg_cursors. If there is a row with that name, the cursor is open.
Here is a self-contained example:
DO
$$DECLARE
c refcursor;
BEGIN
c := 'mycursor';
/* cursor is not open, EXIST returns FALSE */
RAISE NOTICE '%', EXISTS (SELECT 1 FROM pg_cursors WHERE name = 'mycursor');
OPEN c FOR SELECT * FROM pg_class;
/* cursor is open, EXIST returns TRUE */
RAISE NOTICE '%', EXISTS (SELECT 1 FROM pg_cursors WHERE name = 'mycursor');
END;$$;
NOTICE: f
NOTICE: t
If you do not assign a name, PostgreSQL will generate a name (but you don't know what the name is).
PostgreSQL cursors do not support %ISOPEN or %NOTFOUND. To address this problem %ISOPEN can be replaced by a boolean variable declared internally in the procedure and is updated manually when the cursor is opened or closed.
http://wiki.openbravo.com/wiki/PL-SQL_code_rules_to_write_Oracle_and_Postgresql_code
I often found it convenient in cases like this to create a function that emulates Oracle. In his case something like:
create or replace function cursor_isopen(cur text)
returns boolean
language sql
as $$
select exists (select null
from pg_cursors
where name = cur
) ;
$$;
Then your code becomes something like:
exception
when others then
if cursor_isopen(cur_name::text) then
close SPV_RECON_INFO;
end if;
Of course you need to have preset the cursor name as Laurenz Albe has pointed out. Sample test case.
do $$
declare
cur1 cursor for select table_name from information_schema.tables;
cur2 cursor for select table_name from information_schema.tables;
table_name text;
begin
cur1 := 'closed-cursor';
cur2 := 'open-cursor';
open cur2;
if cursor_isopen(cur1::text)
then
fetch cur1 into table_name;
raise notice 'First table name: %', table_name;
close cur1;
else raise notice 'cursor_isopen(''%'') returned %', cur1::text, cursor_isopen(cur1::text);
end if;
if cursor_isopen(cur2::text)
then
fetch cur2 into table_name;
raise notice 'First table name: %', table_name;
close cur2;
else raise notice 'cursor_isopen(''%'') returned %', cur1::text, cursor_isopen(cur1::text);
end if;
end;
$$;
results:
cursor_isopen('closed-cursor') returned f
cursor_isopen('open-cursor') returned t. First table name: task_states
For some fancy database maintenance for my developer database I'd like to be able to use queries to generate commands to alter the database. The thing is: I'm a complete greenhorn to PostgreSQL. I've made my attempt but have failed colorfully.
So in the end, I would like to have a table with a single column and each row would be a command (or group of commands, depending on the case) that I would think would look something like this...
DO $$
DECLARE
command_entry RECORD;
BEGIN
FOR command_entry IN SELECT * FROM list_of_commands
LOOP
EXECUTE command_entry;
END LOOP;
END;
$$;
Where the table list_of_commands could be populated with something like the following (which in this example would remove all tables from the public schema)...
CREATE TEMP TABLE list_of_commands AS
SELECT 'drop table if exists "' || tablename || '" cascade;'
FROM pg_tables
WHERE schemaname = 'public';
However, with this I get the following error...
ERROR: syntax error at or near ""drop table if exists ""dummy_table"" cascade;""
LINE 1: ("drop table if exists ""dummy_table"" cascade;")
I assume this is a matter of escaping characters, but I'm not entirely sure how to fit that into either A) the population of the table or B) the execution of each row. Does anyone know what I could do to achieve the desired result?
The command_entry variable is of type record while the EXECUTE command expects a string. What is apparently happening is that PostgreSQL turns the record into a double-quoted string, but that messes up your command. Also, your temp table does not use a column name, making things a bit awkward to work with (the column name becomes ?column?), so change both as follows:
CREATE TEMP TABLE list_of_commands AS
SELECT 'drop table if exists public.' || quote_ident(tablename) || ' cascade' AS cmd
FROM pg_tables
WHERE schemaname = 'public';
DO $$
DECLARE
command_entry varchar;
BEGIN
FOR command_entry IN SELECT cmd FROM list_of_commands
LOOP
EXECUTE command_entry;
END LOOP;
END;
$$;
But seeing that you do all of this at session level (temp table, anonymous code block), why not write a stored procedure that performs all of this housekeeping when you are ready to do spring cleaning?
CREATE FUNCTION cleanup() RETURNS void AS $$
BEGIN
FOR tbl IN SELECT tablename FROM pg_tables WHERE schemaname = 'public'
LOOP
EXECUTE 'DROP TABLE IF EXISTS ' || quote_ident(tbl) || ' CASCADE';
END LOOP;
-- More housekeeping jobs
END;
$$ LANGUAGE plpgsql;
This saves a lot of typing: SELECT cleanup();. Any other housekeeping jobs you have you simply add to the stored procedure.
I had trouble with Patrick's answers, so here is an updated version for postgreSQL 10.
CREATE FUNCTION droptables(sn varchar) RETURNS void AS $$
DECLARE
tbl varchar;
BEGIN
FOR tbl IN SELECT tablename FROM pg_tables WHERE schemaname = sn
LOOP
EXECUTE 'DROP TABLE IF EXISTS ' || quote_ident(tbl) || ' CASCADE';
END LOOP;
END;
$$ LANGUAGE plpgsql;
And then "SELECT droptables('public');".
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 ...
CREATE OR REPLACE FUNCTION drop_now()
RETURNS void AS
$BODY$
DECLARE
row record;
BEGIN
RAISE INFO 'in';
FOR row IN
select relname from pg_stat_user_tables
WHERE schemaname='public' AND relname LIKE '%test%'
LOOP
IF EXISTS(SELECT row.relname.tm FROM row.relname
WHERE row.relname.tm < current_timestamp - INTERVAL '90 minutes'
LIMIT 1)
THEN
-- EXECUTE 'DROP TABLE ' || quote_ident(row.relname);
RAISE INFO 'Dropped table: %', quote_ident(row.relname);
END IF;
END LOOP;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
Could you tell me how to use variables in SELECT which is inside IF EXISTS? At the present moment, row.relname.tm and row.relname are treated literally which is not I want.
CREATE OR REPLACE FUNCTION drop_now()
RETURNS void AS
$func$
DECLARE
_tbl regclass;
_found int;
BEGIN
FOR _tbl IN
SELECT relid
FROM pg_stat_user_tables
WHERE schemaname = 'public'
AND relname LIKE '%test%'
LOOP
EXECUTE format($f$SELECT 1 FROM %s
WHERE tm < now() - interval '90 min'$f$, _tbl);
GET DIAGNOSTICS _found = ROW_COUNT;
IF _found > 0 THEN
-- EXECUTE 'DROP TABLE ' || _tbl;
RAISE NOTICE 'Dropped table: %', _tbl;
END IF;
END LOOP;
END
$func$ LANGUAGE plpgsql;
Major points
row is a reserved word in the SQL standard. It's use is allowed in Postgres, but it's still unwise. I make it a habbit to prepend psql variable with an underscore _ to avoid any naming conflicts.
You don't don't select the whole row anyway, just the table name in this example. Best use a variable of type regclass, thereby avoiding SQL injection by way of illegal table names automatically. Details in this related answer:
Table name as a PostgreSQL function parameter
You don't need LIMIT in an EXISTS expression, which only checks for the existence of any rows. And you don't need meaningful target columns for the same reason. Just write SELECT 1 or SELECT * or something.
You need dynamic SQL for queries with variable identifiers. Plain SQL does not allow for that. I.e.: build a query string and EXECUTE it. Details in this closely related answer:
Dynamic SQL (EXECUTE) as condition for IF statement
The same is true for a DROP statement, should you want to run it. I added a comment.
You'll need to build your query as a string then execute that - see the section on executing dynamic commands in the plpgsql section of the manual.
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.