My understanding is, within Postgres Database, we can write SQL style user -created function and PlpgSQL style user-created function. And they should be able to translate from one to the other. First off, am I conceptually wrong?
Here is an example:
I was trying to convert such code below:
CREATE OR REPLACE FUNCTION getNthHighestSalary(N integer) RETURNS integer
AS $$
BEGIN
return (
select distinct salary
from employee
order by salary
limit 1 offset $1-1);
END;$$ LANGUAGE plpgsql;
into something like:
CREATE OR REPLACE FUNCTION getNthHighestSalary(N integer) RETURNS integer
AS
BEGIN
return (
select distinct salary
from employee
order by salary
limit 1 offset $1-1);
END; LANGUAGE SQL;
no matter how I tried, the code I converted to won't work inside Postgres database, and always throws weird syntax error.
so how to convert the piece of code above to a viable Standard SQL function which is able to run within Postgres database? especially please explain where the problem is and what's the major difference between Standard SQL and Plpgsql syntax in the Postgres Database environment. Thanks a lot
BTW, here's the code for creating test table and inserting test data:
create table Employee
(
id varchar(255) PRIMARY KEY,
Salary numeric
);
insert into Employee values('1',100),('2',200),('3',300);
If you want to use LANGUAGE SQL, then there are a couple of changes you have to make.
First is to get rid of the BEGIN and END.
Second is to simply state the SELECT query without the RETURN keyword.
There were some other problems: You should order by salary desc, the return type is numeric rather than integer, and you need to escape the ; character, so enclose it with $$ as you do the plpgsql functions.
CREATE OR REPLACE FUNCTION getNthHighestSalary(N integer) RETURNS numeric
AS $$
select distinct salary
from employee
order by salary desc
limit 1 offset $1-1;
$$ LANGUAGE SQL;
Related
I'm new to databases and SQL and i've been messing around with functions on POSTGRESQL and I made a simple function to select all names from a table.
But the function, when called, returns just a single row as opposed to all rows being returned when i use SELECT c_name FROM customers; instead of the code shown below:
CREATE OR REPLACE FUNCTION get_cust_names()
RETURNS varchar AS
$body$
SELECT c_name FROM customers;
$body$
LANGUAGE SQL
Function call
SELECT get_cust_names()
this returns just a SINGLE row and this isnt code that i will use in a project etc. I'm just curious as to why postgresql behaves this way.
You need to declare the function as returns table(..) or returns setof
CREATE OR REPLACE FUNCTION get_cust_names()
RETURNS table(cust_name varchar)
AS
$body$
SELECT c_name
FROM customers;
$body$
LANGUAGE SQL;
Then use it like a table:
select *
from get_cust_names();
I would like to use a plpgsql function with a table and several columns as input parameter. The idea is to split the table in chunks and do something with each part.
I tried the following function:
CREATE OR REPLACE FUNCTION my_func(Integer)
RETURNS SETOF my_part
AS $$
DECLARE
out my_part;
BEGIN
FOR i IN 0..$1 LOOP
FOR out IN
SELECT * FROM my_func2(SELECT * FROM table1 WHERE id = i)
LOOP
RETURN NEXT out;
END LOOP;
END LOOP;
RETURN;
END;
$$
LANGUAGE plpgsql;
my_func2() is the function that does some work on each smaller part.
CREATE or REPLACE FUNCTION my_func2(table1)
RETURNS SETOF my_part2 AS
$$
BEGIN
RETURN QUERY
SELECT * FROM table1;
END
$$
LANGUAGE plpgsql;
If I run:
SELECT * FROM my_func(99);
I guess I should receive the first 99 IDs processed for each id.
But it says there is an error for the following line:
SELECT * FROM my_func2(select * from table1 where id = i)
The error is:
The subquery is only allowed to return one column
Why does this happen? Is there an easy way to fix this?
There are multiple misconceptions here. Study the basics before you try advanced magic.
Postgres does not have "table variables". You can only pass 1 column or row at a time to a function. Use a temporary table or a refcursor (like commented by #Daniel) to pass a whole table. The syntax is invalid in multiple places, so it's unclear whether that's what you are actually trying.
Even if it is: it would probably be better to process one row at a time or rethink your approach and use a set-based operation (plain SQL) instead of passing cursors.
The data types my_part and my_part2 are undefined in your question. May be a shortcoming of the question or a problem in the test case.
You seem to expect that the table name table1 in the function body of my_func2() refers to the function parameter of the same (type!) name, but this is fundamentally wrong in at least two ways:
You can only pass values. A table name is an identifier, not a value. You would need to build a query string dynamically and execute it with EXECUTE in a plpgsql function. Try a search, many related answers her on SO. Then again, that may also not be what you wanted.
table1 in CREATE or REPLACE FUNCTION my_func2(table1) is a type name, not a parameter name. It means your function expects a value of the type table1. Obviously, you have a table of the same name, so it's supposed to be the associated row type.
The RETURN type of my_func2() must match what you actually return. Since you are returning SELECT * FROM table1, make that RETURNS SETOF table1.
It can just be a simple SQL function.
All of that put together:
CREATE or REPLACE FUNCTION my_func2(_row table1)
RETURNS SETOF table1 AS
'SELECT ($1).*' LANGUAGE sql;
Note the parentheses, which are essential for decomposing a row type. Per documentation:
The parentheses are required here to show that compositecol is a column name not a table name
But there is more ...
Don't use out as variable name, it's a keyword of the CREATE FUNCTION statement.
The syntax of your main query my_func() is more like psudo-code. Too much doesn't add up.
Proof of concept
Demo table:
CREATE TABLE table1(table1_id serial PRIMARY KEY, txt text);
INSERT INTO table1(txt) VALUES ('a'),('b'),('c'),('d'),('e'),('f'),('g');
Helper function:
CREATE or REPLACE FUNCTION my_func2(_row table1)
RETURNS SETOF table1 AS
'SELECT ($1).*' LANGUAGE sql;
Main function:
CREATE OR REPLACE FUNCTION my_func(int)
RETURNS SETOF table1 AS
$func$
DECLARE
rec table1;
BEGIN
FOR i IN 0..$1 LOOP
FOR rec IN
SELECT * FROM table1 WHERE table1_id = i
LOOP
RETURN QUERY
SELECT * FROM my_func2(rec);
END LOOP;
END LOOP;
END
$func$ LANGUAGE plpgsql;
Call:
SELECT * FROM my_func(99);
SQL Fiddle.
But it's really just a a proof of concept. Nothing useful, yet.
As the error log is telling you.. you can return only one column in a subquery, so you have to change it to
SELECT my_func2(SELECT Specific_column_you_need FROM hasval WHERE wid = i)
a possible solution can be that you pass to funct2 the primary key of the table your funct2 needs and then you can obtain the whole table by making the SELECT * inside the function
Is it possible to pass the results of a postgres query as an input into another function?
As a very contrived example, say I have one query like
SELECT id, name
FROM users
LIMIT 50
and I want to create a function my_function that takes the resultset of the first query and returns the minimum id. Is this possible in pl/pgsql?
SELECT my_function(SELECT id, name FROM Users LIMIT 50); --returns 50
You could use a cursor, but that very impractical for computing a minimum.
I would use a temporary table for that purpose, and pass the table name for use in dynamic SQL:
CREATE OR REPLACE FUNCTION f_min_id(_tbl regclass, OUT min_id int) AS
$func$
BEGIN
EXECUTE 'SELECT min(id) FROM ' || _tbl
INTO min_id;
END
$func$ LANGUAGE plpgsql;
Call:
CREATE TEMP TABLE foo ON COMMIT DROP AS
SELECT id, name
FROM users
LIMIT 50;
SELECT f_min_id('foo');
Major points
The first parameter is of type regclass to prevent SQL injection. More info in this related answer on dba.SE.
I made the temp table ON COMMIT DROP to limit its lifetime to the current transaction. May or may not be what you want.
You can extend this example to take more parameters. Search for code examples for dynamic SQL with EXECUTE.
-> SQLfiddle demo
I would take the problem on the other side, calling an aggregate function for each record of the result set. It's not as flexible but can gives you an hint to work on.
As an exemple to follow your sample problem:
CREATE OR REPLACE FUNCTION myMin ( int,int ) RETURNS int AS $$
SELECT CASE WHEN $1 < $2 THEN $1 ELSE $2 END;
$$ LANGUAGE SQL STRICT IMMUTABLE;
CREATE AGGREGATE my_function ( int ) (
SFUNC = myMin, STYPE = int, INITCOND = 2147483647 --maxint
);
SELECT my_function(id) from (SELECT * FROM Users LIMIT 50) x;
It is not possible to pass an array of generic type RECORD to a plpgsql function which is essentially what you are trying to do.
What you can do is pass in an array of a specific user defined TYPE or of a particular table row type. In the example below you could also swap out the argument data type for the table name users[] (though this would obviously mean getting all data in the users table row).
CREATE TYPE trivial {
"ID" integer,
"NAME" text
}
CREATE OR REPLACE FUNCTION trivial_func(data trivial[])
RETURNS integer AS
$BODY$
DECLARE
BEGIN
--Implementation here using data
return 1;
END$BODY$
LANGUAGE 'plpgsql' VOLATILE;
I think there's no way to pass recordset or table into function (but I'd be glad if i'm wrong). Best I could suggest is to pass array:
create or replace function my_function(data int[])
returns int
as
$$
select min(x) from unnest(data) as x
$$
language SQL;
sql fiddle demo
I got Postgresql 8.4
I have a user table
user_id INT,
user_name VARCHAR(255),
user_email VARCHAR(255),
user_salt VARCHAR(255)
and 2 functions:
one with SETOF:
CREATE FUNCTION test ()
RETURNS SETOF "user"
AS
$BODY$
BEGIN
RETURN QUERY SELECT
*
FROM
"user";
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
one with TABLE:
CREATE FUNCTION test ()
RETURNS TABLE (id INT, name VARCHAR, email VARCHAR)
AS
$BODY$
BEGIN
RETURN QUERY SELECT
"user".user_id, "user".user_name, "user".user_email
FROM
"user";
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
By SETOF the column type is filled automatically, but I cannot set the column name and which columns to select in the result. By TABLE I can cut off the user_ prefix and set the exact column names, but I have to set the column types manually.
Is it possible to got the advantages of both?
Type handling with in PostgreSQL (and SQL in general) is strict. Defining the RETURN type of a function can be tricky.
There are simple solutions with plain SQL:
Select and rename all columns:
SELECT * FROM t AS t(id, name, email, salt);
Select and rename some columns:
SELECT user_id AS id, user_name AS name FROM t;
Combine with function
If you need a server side function for some reason, you can still combine these SQL features with a function. Given a table t like defined in your question and this simple function:
CREATE OR REPLACE FUNCTION f_test()
RETURNS SETOF t AS
$func$
SELECT * FROM t -- do stuff here
$func$ LANGUAGE sql STABLE;
To only rename columns (no need to provide types):
SELECT * FROM f_test() t(id, name, email, salt)
Select and rename some columns:
SELECT user_id AS id, user_name AS name FROM f_test() t;
You could possibly combine this with various different functions on different tables:
Refactor a PL/pgSQL function to return the output of various SELECT queries
But I am not entirely sure which problem in particular you want to tackle here.
Asides
Never quote the language name. plpgsql is an identifier. Quoting can lead to unexpected problems.
A function that only selects from tables can be declared STABLE. May be beneficial with repeated calls when nested.
Generally I would advice to upgrade to a current version of Postgres. 8.4 is rather old and will be lose support in less than a year. There have been a number of improvements in this area since 8.4.
I don't think this is possible in pl/pgsql because, it strongly depends on user defined types. Sadly this language is not smart enough for type auto detection... I think my first possible solution I'll use, it solves the problem partially because at least I won't need to refactor every function manually by type change of a table column.
1.) Possible solution with asking column types:
CREATE FUNCTION test ()
RETURNS TABLE (id "user".user_id%TYPE, name "user".user_name%TYPE, email "user".user_email%TYPE)
AS
$BODY$
BEGIN
return QUERY SELECT
"user".user_id, "user".user_name, "user".user_email
FROM
"user";
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
With this at least the type is not redundant. Not the best, but acceptable.
2.) Possible solution with SETOF RECORD:
CREATE FUNCTION test ()
RETURNS SETOF RECORD
AS
$BODY$
BEGIN
RETURN QUERY SELECT
"user".user_id AS id, "user".user_name AS name, "user".user_email AS email
FROM
"user";
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
Without column type definition list I got the following error:
ERROR: a column definition list is required for functions returning
"record"
So I have to use it like this:
SELECT * FROM test() AS (id INT, name VARCHAR, email VARCHAR);
Instead of this:
SELECT * FROM test()
I got every column in string by the php client, so the column type definition is more than useless for me... This solution would be the best without column type definition, but with it not acceptable.
It is possible to use this similar to table:
CREATE FUNCTION test (OUT id "user".user_id%TYPE, OUT name "user".user_name%TYPE, OUT email "user".user_email%TYPE)
RETURNS SETOF RECORD
AS
$BODY$
BEGIN
RETURN QUERY SELECT
"user".user_id, "user".user_name, "user".user_email
FROM
"user";
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
For example I could set everything to TEXT:
CREATE FUNCTION test (OUT id TEXT, OUT name TEXT , OUT email TEXT )
RETURNS SETOF RECORD
AS
$BODY$
BEGIN
RETURN QUERY SELECT
"user".user_id::TEXT , "user".user_name::TEXT , "user".user_email::TEXT
FROM
"user";
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
This works, but this is far from type auto detection, and it would result a lot of redundant text converter code...
3.) Possible solution with refcursors:
CREATE FUNCTION test ()
RETURNS SETOF "user"
AS
$BODY$
DECLARE
refc "user";
BEGIN
FOR refc IN
SELECT
"user".user_id, "user".user_name, "user".user_email
FROM
"user"
LOOP
RETURN NEXT refc;
END LOOP ;
RETURN ;
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
This fills out the lacking columns with null values, I cannot name the columns, and sql loops are very slow... So this is not acceptable.
By refcursors there is another way: to return the refcursor itself, but it is not acceptable because I cannot use it as a normal variable, I have to give a string as cursor name... Btw I did not manage to use the refcursor itself as result in phpstorm. I got jdbc cursor not found error. Maybe I set the name wrong, I don't know, I don't think it's worth more effort.
i've serarched for the answer, but did't find.
so i've got a table types
CREATE TABLE types
(
type_id serial NOT NULL,
type_name character varying,
CONSTRAINT un_type_name UNIQUE (type_name)
)
which holds type names, lets say users - and this is the name of corresponding table users. this design may be a bit ugly, but it was made to allow users create their own types. (is there better way to acheve this?)
now i want to perform a query like this one:
select type_name, (select count(*) from ???) from types
to get list of all type names and count of objects of each type.
can this be done?
You cannot do it directly in SQL
You can use a PLpgSQL function and dynamic SQL
CREATE OR REPLACE FUNCTION tables_count(OUT type_name character varying, OUT rows bigint)
RETURNS SETOF record AS $$
BEGIN
FOR tables_count.type_name IN SELECT types.type_name FROM types
LOOP
EXECUTE 'SELECT COUNT(*) FROM ' || quote_ident(tables_count.type_name) INTO tables_count.rows;
RETURN NEXT;
END LOOP;
RETURN;
END;
$$ LANGUAGE plpgsql;
SELECT * FROM tables_count();
I don't have enough information, but I do suspect that something is off with your design. You shouldn't need an extra table for every type.
Be that as it may, what you want to do cannot be done - in pure SQL.
It can be done with a plpgsql function executing dynamic SQL, though:
CREATE OR REPLACE FUNCTION f_type_ct()
RETURNS TABLE (type_name text, ct bigint) AS
$BODY$
DECLARE
tbl text;
BEGIN
FOR tbl IN SELECT t.type_name FROM types t ORDER BY t.type_name
LOOP
RETURN QUERY EXECUTE
'SELECT $1, count(*) FROM ' || tbl::regclass
USING tbl;
END LOOP;
END;
$BODY$
LANGUAGE plpgsql;
Call:
SELECT * FROM f_type_ct();
You'll need to study most of the chapter about plpgsql in the manual to understand what's going on here.
One special hint: the cast to regclass is a safeguard against SQLi. You could also use the more generally applicable quote_ident() for that, but that does not properly handle schema-qualified table names, while the cast to regclass does. It also only accepts table names that are visible to the calling user.