I am scratching my head on this since a while. I am trying to create a materialized view and I want the query to be parallel. However when I use the following code :
CREATE MATERIALIZED VIEW xxx AS SELECT foo(myfield) FROM table
I got the following error :
cannot start subtransactions during a parallel operation
CONTEXT: PL/pgSQL function foo(text) line 1 during statement block entry
foo is a plpgsql function and as such considered as a subtransaction. However you can see there is nothing magic, I use it only to handle exceptions :
CREATE FUNCTION foo(TEXT) RETURNS NUMERIC LANGUAGE plpgsql IMMUTABLE PARALLEL SAFE AS $$
BEGIN RETURN CAST(REPLACE($1,',','.') AS NUMERIC);
EXCEPTION
WHEN invalid_text_representation THEN RETURN NULL;
END; $$;
How can I create this view in a parallel way and still handle casting exceptions thanks to this plpgsql function ? Is there an other way to handle exceptions ? (try_catch from SQL server would be the fix here but sadly it's postgres).
Thanks !
Check the number for correctness first:
CREATE FUNCTION foo(text) RETURNS numeric
LANGUAGE sql IMMUTABLE PARALLEL SAFE AS
$$SELECT CASE WHEN $1 ~ '^-?[0-9]+(?:,[0-9]+)?$'
THEN CAST (replace($1,',','.') AS numeric);
ELSE CAST (NULL AS numeric)
END$$;
Related
We started to use Postgres much more recently, having moved from SQL Server. I've noticed that Postgres parser/compiler allows creation of functions that (it seems to me) can be rejected at creation time.
One example of what I'm talking about is select statements in plpgsql blocks:
create or replace function test() returns void as $$
begin
select * from pg_database;
end;
$$ language plpgsql;
This function fails at runtime with "query has no destination for result data". Why would this error not be caught at function creation time? Is there any case when using select without 'return' in plpgsql block is allowed?
The other type of errors that are not always caught at compile time is type mismatch errors between a declared return type and actual type of the value. These are caught in simple cases, but start to make it to runtime in more complicated functions. I suspect there's some limitations in Postgres type inference/analysis, is there any additional information on this available?
tldr: Is there any way to make Postgres parser/compiler fail more on function creation?
Is there any way to make Postgres parser/compiler fail more on function creation?
That's the purpose of the plpgsql_check extension. It won't prevent the function to be created, though.
test=# create extension plpgsql_check;
CREATE EXTENSION
test=# create or replace function test() returns void as $$
begin
select * from pg_database;
end;
$$ language plpgsql;
test=# select * from plpgsql_check_function('test');
plpgsql_check_function
----------------------------------------------------------------------
error:42601:3:SQL statement:query has no destination for result data
I need to create a new procedure/function in Postgres that creates a new sequence.
The procedure/function will get the name of the sequence as a variable and creates it.
I tried to follow the documentation but it's not very helpful. This is what I've got so far but it's not working (of course):
CREATE FUNCTION create_seq(text) RETURNS text
AS 'CREATE SEQUENCE $1 START 100;'
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
ERROR: return type mismatch in a function declared to return text
DETAIL: Function's final statement must be SELECT or INSERT/UPDATE/DELETE RETURNING.
CONTEXT: SQL function "create_seq"```
you need use dynamic SQL like said #a_horse_with_no_name, but you need use the plpgsql language not sql language for the function, for remember return void,example,:
CREATE FUNCTION create_seq_plpgsql(p_seq_name text)
RETURNS void
AS
$$
begin
execute format('CREATE SEQUENCE %I START 100', p_seq_name);
end;
$$
LANGUAGE plpgsql;
You need dynamic SQL for that, parameters can't be used as identifiers.
To properly deal with names that potentially need quoting, it is highly recommended to use the format() function to generate the SQL.
And you need to declare the function as returns void as you don't want to return anything.
CREATE FUNCTION create_seq(p_seq_name, text)
RETURNS void
AS
$$
begin
execute format('CREATE SEQUENCE %I START 100', p_seq_name);
end;
$$
LANGUAGE plpgsql;
If you are on Postgres 11, you could also use a procedure instead of a function for that.
I'm trying to store a simple SELECT query with the new CREATE PROCEDURE method in PostgreSQL 11. My idea is to store the queries in the DB, because I can have a much simple code in my API server and maybe I don't need to develop a query builder if I can use if/else in an sql function with enforced type safety. I have this minimal example:
First I tried this plpgsql function:
CREATE OR REPLACE PROCEDURE test_proc() AS $$
BEGIN
SELECT * FROM my_db
LIMIT 1;
END;
$$ LANGUAGE plpgsql;
CALL test_proc();
However throws this error:
ERROR: query has no destination for result data
HINT: If you want to discard the results of a SELECT, use PERFORM instead.
CONTEXT: PL/pgSQL function test_proc() line 3 at SQL statement SQL state: 42601
If I trying to use RETURN QUERY:
CREATE OR REPLACE PROCEDURE test_proc() AS $$
BEGIN
RETURN QUERY;
SELECT * FROM my_db
LIMIT 1;
END;
$$ LANGUAGE plpgsql;
I'm getting this error:
ERROR: cannot use RETURN QUERY in a non-SETOF function
LINE 17: RETURN QUERY; ^
SQL state: 42804
Character: 310
I'm also getting error when I try to use RETURNS void AS $$ or RETURNS table(...) AS $$. Seems like RETURNS not supported in CREATE PROCEDURE? So, is it possible to return a table with the new stored procedure method? Or if it's not, maybe JSON?
Procedures in PostgreSQL (Oracle, DB2) are not same like procedures in MS-SQL. It has different target, and you cannot use it. Usually, the best what you can do, forgot all what you know from MSSQL. The procedural part is really different.
Only functions can returns some data - so you need to use functions. Functions can returns scalar value, composite value or array value, or table. You want function that returns table.
CREATE OR REPLACE FUNCTION fx()
RETURNS SETOF mytab AS $$
BEGIN
RETURN QUERY SELECT * FROM mytab;
END
$$ LANGUAGE plpgsql;
SELECT * FROM fx();
For record:
You can use SQL function, that can have better (or worse) performance (depends on context). These functions are sometimes named as parametrized views.
CREATE OR REPLACE FUNCTION fx()
RETURNS SETOF mytab AS $$
SELECT * FROM mytab;
$$ LANGUAGE sql;
Attention: this technique is antipattern!!! Don't do it. It is really not good idea. The functions should not to wrap queries. If you want to hide some complexity of queries, then use a views. Don't use a functions. Functions are effective barier for query optimizer, and when you use this antipattern, then optimizer cannot to well optimize any non trivial queries that use in this form evaluated subqueries.
Use it - if you want very very slow applications - or if your data model or queries are primitive. In other cases, don't do it.
Don't afraid of SQL - it is great language designed for manual usage. It is good to place all data access to one module (model), to don't access database everywhere in your code, but it is bad too hide SQL in your code.
First of all Procedure was introduced in PostgreSQL 11, If you are using below 11th version, you cannot use Procedures. Instead to Procedure you can use functions.
Syntax to create function
CREATE or replace function function_name(_parameter varchar)
returns table(col1 varchar, col2 varchar, col3 varchar)
language 'plpgsql'
as $BODY$
BEGIN
return query select a.col1, a.col2, b.col3 from table a
join table2 as b on a.col1 = b.col1;
END;
$BODY$;
you can call a function same a like table
select * From function_name('sample data');
syntax to create Procedure.
CREATE OR REPLACE PROCEDURE procedure_name(_parameter varcar,INOUT result refcursor)
LANGUAGE 'plpgsql'
AS $BODY$
BEGIN
open result for SELECT , * from sampletable where a = _parameter;
END;
$BODY$;
you can execute a Procedure using call keyword, within a transaction
BEGIN;
CALL public.procedure_name( 'sample data', 'test');
fetch all in "test";
COMMIT;
The postgreSql 11. we have to create a stored procedure
there is the solution :
Create procedure to execute query in PostgreSQL
I am trying to implement a function that returns a table with the same structure as an input table in the parameter, using PL/pgSQL (PostgreSQL 9.3). Basically, I want to update a table, and return a copy of the updated table with plpgsql. I searched around SO and found several related questions (e.g. Return dynamic table with unknown columns from PL/pgSQL function and Table name as a PostgreSQL function parameter), which lead to the following minimal test example:
CREATE OR REPLACE FUNCTION change_val(_lookup_tbl regclass)
RETURNS _lookup_tbl%rowtype AS --problem line
$func$
BEGIN
RETURN QUERY EXECUTE format('UPDATE %s SET val = 2 RETURNING * ; ', _lookup_tbl);
END
$func$ LANGUAGE plpgsql;
But I can't get past giving the correct return type for TABLE or SETOF RECORD in the problem line. According to this answer:
SQL demands to know the return type at call time
But I think the return type (which I intend to borrow from the input table type) is known. Can some one help explain if it is possible to fix the signature of the above PL/pgSQL function?
Note, I need to parametrize the input table and return the update of that table. Alternatives are welcome.
What you have so far looks good. The missing ingredient: polymorphic types.
CREATE OR REPLACE FUNCTION change_val(_tbl_type anyelement)
RETURNS SETOF anyelement -- problem solved
LANGUAGE plpgsql AS
$func$
BEGIN
RETURN QUERY EXECUTE format(
'UPDATE %s SET val = 2 RETURNING *;'
, pg_typeof(_tbl_type))
);
END
$func$;
Call (important):
SELECT * FROM change_val(NULL::some_tbl);
db<>fiddle here
Old sqlfiddle
See (last paragraph):
Refactor a PL/pgSQL function to return the output of various SELECT queries
I need to show the Tree_Nodes table data
CREATE OR REPLACE FUNCTION sample()
RETURNS TABLE() AS
$BODY$
BEGIN
select * from "Tree_Nodes";
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100
ROWS 1000;
ALTER FUNCTION sample()
OWNER TO postgres;
It fails with:
ERROR: query has no destination for result data
Avoid the error and i will get the table column format in all data
To return the result of a SELECT, a pure SQL function is much more suitable:
CREATE OR REPLACE FUNCTION sample()
RETURNS TABLE ( .... ) AS
$BODY$
select * from "Tree_Nodes";
$BODY$
LANGUAGE sql;
Or if you really need PL/pgSQL, you need to use return query (which is clearly documented in the manual)
CREATE OR REPLACE FUNCTION sample()
RETURNS TABLE (....)
AS
$BODY$
BEGIN
return query select * from "Tree_Nodes";
END;
$BODY$
LANGUAGE plpgsql;
But you cannot just specify returns table() you have to also define the structure of the result:
CREATE OR REPLACE FUNCTION sample()
RETURNS TABLE(id integer, some_column text, other_column decimal(10,2), ...)
AS
The exact error you quote is caused by using SELECT without an INTO clause in PL/PgSQL. You must either use SELECT INTO somevariable, use RETURN QUERY, if you want to discard the data, use the PERFORM statement instead of SELECT, as covered by the PL/PgSQL manual.
Once you fix that by using RETURN QUERY SELECT .... you'll find that the function still doesn't work, because RETURNS TABLE() doesn't make sense. You're returning an empty result set. It'll fail, complaining that the statement is returning a result set that doesn't match the function.
It makes no sense to do this anyway, since you can just write it as a trivial SQL function like:
CREATE OR REPLACE FUNCTION sample()
RETURNS SETOF "Tree_Nodes"
AS $$
SELECT * FROM "Tree_Nodes";
$$ LANGUAGE sql;
This function appears to serve no purpose. What are you trying to achieve with it?
(By the way, you should generally avoid SELECT * in production code. List the columns. That way, if you add a column later, things that use the table won't suddenly stop working.)