I am researching if it is possible to dynamically create a view and then return all data from it, all in a single function. My goal is to create a single function that will return all data from a dynamically created view, upon execution of the function. I can do it in Oracle and SQL Server, but so far I am not sure if it is that simple in Postgres. If someone could show code samples, ideas or point me in the right direction, I would be super happy :)
I already know how to create a SETOF function or a dynamic SQL function, but getting both to work in a single program/function function is a challenge that I cannot overcome so far ...
The returned content can be dynamic, the structure should be static.
CREATE OR REPLACE FUNCTION fx(OUT a int, OUT b int)
RETURNS SETOF record AS $$
BEGIN
RETURN QUERY EXECUTE format('SELECT i, i+1 FROM generate_series(1,3)');
END;
PostgreSQL documentation is good, please, don't be afraid to read it. The plpgsql related pages need no more than two hours.
Related
inside an anonymous block, I have nested a declare...begin...end. Inner block cannot "see" a temp table created in outer block. What is best way to solve, still maintaining creating of temp table inside?
The below FAILs with: CONTEXT: compilation of PL/pgSQL function "inline_code_block" near line 152
do
$$
declare
xyz...
being
create temp table x ... <depending on xyz>
...
declare
r x%rowtype -> FAIL
begin
...
end;
end;
$$
It cannot to work. This error is not related to block scopes, but it is related to timing. The temp table is created in runtime, but the x%rowtype is evaluated in validation time (before runtime). There is very simple and robust solution in Postgres. Use record type:
declare r record;
begin
The variable of record type takes real composite type in assign time.
Although PL/pgSQL is similar to PL/SQL, inside it is absolutely different technology, and not all patterns from Oracle are possible or are effective. And sometimes there are different (and sometimes much more comfortable) ways.
So I have a function in PostgreSQL that dynamically selects columns from a dynamic table. I got this solution from this post and it works great other than one thing.
This is inside of a file that is connected to a Node server, and so the $1 and $2 in the second SELECT * FROM represent values passed from there. The issue right now is that I am getting a syntax error that I don't understand (I am newer to SQL so that may be why).
$2 represents the name of the table to be selected from as a string, so for example it could be 'goals'. The error is syntax error at or near "'goals'". I realize that it cannot be a string with single quotes (I believe) and so I am wondering how to convert that variable to be a table name? using "goals" there as well as goals, for example works as expected, though I'm not sure how to do that outside of a function.
CREATE OR REPLACE FUNCTION get_data(user_id INT, table_name anyelement)
RETURNS SETOF ANYELEMENT AS $$
BEGIN
RETURN QUERY EXECUTE
format('SELECT * FROM %s WHERE user_id = $1', pg_typeof(table_name)) USING user_id;
END;
$$ LANGUAGE plpgsql;
SELECT * FROM get_data($1, NULL::$2);
$1 is 5 and $2 is 'goals' for example
After many hours of trying to figure it out, thanks to Adrian's comment, I found MassiveJS (how I'm connecting to my PostgreSQL server) has inline functions to do queries. In my controller file in my server I was able to create a one line function as such:
const data = await db[tableName].where("user_id=$1", [userId])
Didn't know inline SQL existed in MassiveJS, so that was great to find out!
If an entry in a table satisfies certain conditions, a NOTIFY is sent out. I want the payload to include the ID number and several other columns of information. Is there a postgres method to convert variables (OLD.ColumnID, etc) to strings?
using postgres 9.3
#klin is correct that NOTIFY doesn't support anything other than string literals. However there is a function pg_notify() which takes normal arguments to deal with exactly this situation. It's been around since at least 9.0 and that link is to the official documentation - always worth reading it carefully, there is a wealth of information there.
My guess is that the notify has to be done within a trigger function. Use a dynamic query, e.g.
execute format('notify channel, ''id: %s''', old.id);
The solution was to upgrade Postgres to a version that supported JSON.
Even postgresql 9.3 supports json. You could have just used row_to_json(payload)::text
Sorry for the long answer, i just cant walk away without reacting to the other answers too.
The format version fails in many ways. Before EXECUTE, you shoud prepare the plan. The "pseudo command" does not fits the syntax of execute which is
EXECUTE somepreparedplanname (parameter1, ...)
The %s in format is again too bad, this way you can summon sql injection attacks. When constructing a query with format, you need to use %L for literals %I for column/table/function/etc ids, and use %s almost never.
The other solution with the pg_notify function is correct. Try
LISTEN channel;
SELECT pg_notify('channel','Id: '|| pg_backend_pid ());
in psql command line.
So back to the original question: sdemurjian,
Its not clarified in the question, if you wants to use this notification thing in some trigger function. So here is an example (maybe not) for you (because im a little late. sorry for that too):
CREATE TABLE columns("columnID" oid, "columnData" text);
CREATE FUNCTION column_trigger_func() RETURNS TRIGGER AS
$$ BEGIN PERFORM pg_notify('columnchannel', 'Id: '||OLD."columnID");
RETURN NEW; END; $$ LANGUAGE plpgsql;
CREATE TRIGGER column_notify BEFORE UPDATE ON columns FOR EACH ROW
EXECUTE PROCEDURE column_trigger_func();
LISTEN columnchannel;
INSERT INTO columns VALUES(1,'testdata');
BEGIN; UPDATE columns SET "columnData" = 'success'; END;
BEGIN; UPDATE columns SET "columnData" = 'fail'; ROLLBACK;
Please note that in early postgres versions (any before 9), the notify command does not accepts any payload and there is no pg_notify function.
In 8.1 the trigger function stil works if you define it like
CREATE FUNCTION column_trigger_func() RETURNS TRIGGER AS
$$ BEGIN NOTIFY columnchannel; RETURN NEW; END; $$ LANGUAGE plpgsql;
I would love to exploit the SQL output formatting of PostgreSQL inside my PL/pgSQL functions, but I'm starting to feel I have to give up the idea.
I have my PL/pgSQL function query_result:
CREATE OR REPLACE FUNCTION query_result(
this_query text
) RETURNS SETOF record AS
$$
BEGIN
RETURN QUERY EXECUTE this_query;
END;
$$ LANGUAGE plpgsql;
..merrily returning a SETOF records from an input text query, and which I can use for my SQL scripting with dynamic queries:
mydb=# SELECT * FROM query_result('SELECT ' || :MYVAR || ' FROM Alice') AS t (id int);
id
----
1
2
3
So my hope was to find a way to deliver this same nicely formatted output from inside a PL/pgSQL function instead, but RAISE does not support SETOF types, and there's no magic predefined cast from SETOF records to text (I know I could create my own CAST..)
If I create a dummy print_result function:
CREATE OR REPLACE FUNCTION print_result(
this_query text
) RETURNS void AS
$$
BEGIN
SELECT query_result(this_query);
END;
$$ LANGUAGE plpgsql;
..I cannot print the formatted output:
mydb=# SELECT print_result('SELECT ' || :MYVAR || ' FROM Alice');
ERROR: set-valued function called in context that cannot accept a set
...
Thanks for any suggestion (which preferably works with PostgreSQL 8.4).
Ok, to do anything with your result set in print_result you'll have to loop over it. That'll look something like this -
Here result_record is defined as a record variable. For the sake of explanation, we'll also assume that you have a formatted_results variable that is defined as text and defaulted to a blank string to hold the formatted results.
FOR result_record IN SELECT * FROM query_result(this_query) AS t (id int) LOOP
-- With all this, you can do something like this
formatted_results := formatted_results ||','|| result_record.id;
END LOOP;
RETURN formatted_results;
So, if you change print_results to return text, declare the variables as I've described and add this in, your function will return a comma-separated list of all your results (with an extra comma at the end, I'm sure you can make use of PostgreSQL's string functions to trim that). I'm not sure this is exactly what you want, but this should give you a good idea about how to manipulate your result set. You can get more information here about control structures, which should let you do pretty much whatever you want.
EDIT TO ANSWER THE REAL QUESTION:
The ability to format data tuples as readable text is a feature of the psql client, not the PostgreSQL server. To make this feature available in the server would require extracting relevant code or modules from the psql utility and recompiling them as a database function. This seems possible (and it is also possible that someone has already done this), but I am not familiar enough with the process to provide a good description of how to do that. Most likely, the best solution for formatting query results as text will be to make use of PostgreSQL's string formatting functions to implement the features you need for your application.
How do I convert a simple select query like select * from customers into a stored procedure / function in pg?
I'm new to Postgres and create function customers() as returns table/setof just didn't feel right and thus the question here.
I understand procs are called "functions" in pg land. Thus create procedure does not exist and my only options are to either create a view or a function. The issue is create function x() returns setof y returns a paren'd comma separated row of values which can't be used without further processing (at least that's what I'm seeing in pgAdmin and Ruby/Sequel).
create function x() returns table(...) requires I embed the row definition which I don't want to.
I'm sure there's a reason behind all this but I'm surprised that the most common use case is this tricky.
Untested but should be about right:
CREATE OR REPLACE FUNCTION getcustomers() RETURNS SETOF customers AS $$
SELECT * FROM customers;
$$ LANGUAGE sql;
The issue is "create function x() returns setof y" returns a paren'd
comma separated row values which can't be used without further processing
The function returns a row. To decompose into individual columns, call it with:
SELECT * FROM getcustomers();
That's assuming the function defines a proper return type. See:
How to return multiple rows from PL/pgSQL function?
The manual on CREATE FUNCTION should be a good starting point. The example section covers this topic.