If I have these two Postgres function definitions saved in two seperate .sql files:
CREATE OR REPLACE FUNCTION column_exists(tablename text, colname text) RETURNS boolean AS
$BODY$
DECLARE
q text;
field_name text;
onerow record;
BEGIN
q = 'SELECT column_name FROM information_schema.columns WHERE table_name='''||tablename||''' AND table_schema =''public''';
FOR onerow IN EXECUTE q
LOOP
field_name := onerow.column_name;
IF ((field_name = colname)) then
RETURN true;
END IF;
END LOOP;
RETURN false;
END;
$BODY$
LANGUAGE plpgsql
CREATE OR REPLACE FUNCTION correct_col_names() RETURNS VOID AS
$BODY$
DECLARE
q boolean;
BEGIN
-- rename name column to Name
select column_exists('National_Parks', 'name') as q;
IF q = TRUE THEN
alter table "National_Parks"
rename column name to "Name";
END IF;
-- remance descriptio column to description
select column_exists('National_Parks', 'descriptio') as q;
IF q = TRUE THEN
alter table "Natioanl_Parks"
rename column descriptio to "Description";
END IF;
END
$BODY$
LANGUAGE plpgsql
What is the syntax I need to use to call the sequentially, say in another script? I tried
select correct_col_names()
and this returns the following 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 "correct_col_names" line 7 at SQL statement
********** Error **********
ERROR: query has no destination for result data
SQL state: 42601
Hint: If you want to discard the results of a SELECT, use PERFORM instead.
Context: PL/pgSQL function "correct_col_names" line 7 at SQL statement
TIA.
The problem is that you have SELECT statements that aren't doing anything with the data. Your
select column_exists('National_Parks', 'name') as q;
should be
select column_exists('National_Parks', 'name') INTO q;
The as simply aliases the result as "q" for that query, it doesn't actually put it into the q variable.
Your syntax for calling the functions (select correct_col_names()) is correct for SQL. Once you fix the two errors in that function, it should work.
However, if you were to try select correct_col_names() inside another PL/PGSQL function, you would get the same error, because the select statement isn't actually doing anything with the results. perform correct_col_names() would run without error, because PERFORM is PL/PGSQL syntax for calling something when you don't want to save the result.
Related
CREATE FUNCTION retrieve_add_friends(user_id text[])
RETURNS SETOF user_rows AS
$BODY$
BEGIN
FOR user_rows IN EXECUTE SELECT * FROM user_details where user_id= $1
LOOP
FOR user_friends IN EXECUTE SELECT * FROM user_add_friends where user_id= $1
LOOP
IF user_rows.user_id!=user_friends.user_friend_id THEN
RETURN NEXT user_rows;
END IF;
END LOOP;
RETURN;
END LOOP;
RETURN;
END
$BODY$
language plpgsql VOLATILE;
When I execute this I get following error:
ERROR: return type mismatch in function declared to return user_details
DETAIL: Function's final statement must be SELECT or INSERT/UPDATE/DELETE RETURNING.
CONTEXT: SQL function "retrieve_add_friends"
Can anyone help me out with this?
The function displayed is a PL/pgSQL function.
You are calling a different function, an SQL function, obviously (for which the error msg would make sense):
SQL function "retrieve_add_friends"
Same function name, but different arguments (and possibly in a different database schema). Are you aware of function overloading and its implications?
Related:
ERROR: function addgeometrycolumn is not unique
For a quick diagnosis:
SELECT oid::regprocedure AS function_signature, *
FROM pg_proc
WHERE proname = 'retrieve_add_friends';
All that aside, the function displayed has multiple errors and can be replaced with plain SELECT.
The function is created fine, but when I try to execute it, I get this error:
ERROR: relation "column1" does not exist
SQL state: 42P01
Context: SQL statement "ALTER TABLE COLUMN1 ADD COLUMN locationZM geography (POINTZM, 4326)"
PL/pgSQL function addlocationzm() line 6 at SQL statement
Code:
CREATE OR REPLACE FUNCTION addlocationZM()
RETURNS void AS
$$
DECLARE
COLUMN1 RECORD;
BEGIN
FOR COLUMN1 IN SELECT f_table_name FROM *schema*.geography_columns WHERE type LIKE 'Point%' LOOP
ALTER TABLE COLUMN1 ADD COLUMN locationZM geography (POINTZM, 4326);
END LOOP;
END;
$$
LANGUAGE 'plpgsql';
SELECT addlocationZM()
I'm probably just being dumb, but I've been at this for a while now and I just can't get it. The SELECT f_table_name ... statement executed on its own returns 58 rows of a single column, each of which is the name of a table in my schema. The idea of this is to create a new column, type PointZM, in each table pulled by the SELECT.
The function would work like this:
CREATE OR REPLACE FUNCTION addlocationZM()
RETURNS void AS
$func$
DECLARE
_tbl text;
BEGIN
FOR _tbl IN
SELECT f_table_name FROM myschema.geography_columns WHERE type LIKE 'Point%'
LOOP
EXECUTE
format('ALTER TABLE %I ADD COLUMN location_zm geography(POINTZM, 4326)', _tbl);
END LOOP;
END
$func$ LANGUAGE plpgsql;
Note how I use a simple text variable to simplify matters. You don't need the record to begin with.
If it's a one-time operation, use a DO command instead of creating a function:
DO
$do$
BEGIN
EXECUTE (
SELECT string_agg(
format(
'ALTER TABLE %I ADD COLUMN location_zm geography(POINTZM, 4326);'
, f_table_name)
, E'\n')
FROM myschema.geography_columns
WHERE type LIKE 'Point%'
);
END
$do$;
This is concatenating a single string comprised of all commands (separated with ;) for a single EXECUTE.
Or, especially while you are not familiar with plpgsql and dynamic SQL, just generate the commands, copy/paste the result and execute as 2nd step:
SELECT 'ALTER TABLE '
|| quote_ident(f_table_name)
|| ' ADD COLUMN locationZM geography(POINTZM, 4326);'
FROM myschema.geography_columns
WHERE type LIKE 'Point%';
(Demonstrating quote_ident() this time.)
Related:
Table name as a PostgreSQL function parameter
Aside: Unquoted CaMeL-case identifiers like locationZM or your function name addlocationZM may not be such a good idea:
Are PostgreSQL column names case-sensitive?
I need to do the same deletion or purge operation (based on several conditions) on a set of tables. For that I am trying to pass the table names in an array to a function. I am not sure if I am doing it right. Or is there a better way?
I am pasting just a sample example this is not the real function I have written but the basic is same as below:
CREATE OR REPLACE FUNCTION test (tablename text[]) RETURNS int AS
$func$
BEGIN
execute 'delete * from '||tablename;
RETURN 1;
END
$func$ LANGUAGE plpgsql;
But when I call the function I get an error:
select test( {'rajeev1'} );
ERROR: syntax error at or near "{"
LINE 10: select test( {'rajeev1'} );
^
********** Error **********
ERROR: syntax error at or near "{"
SQL state: 42601
Character: 179
Array syntax
'{rajeev1, rajeev2}' or ARRAY['rajeev1', 'rajeev2']. Read the manual.
TRUNCATE
Since you are deleting all rows from the tables, consider TRUNCATE instead. Per documentation:
Tip: TRUNCATE is a PostgreSQL extension that provides a faster
mechanism to remove all rows from a table.
Be sure to study the details. If TRUNCATE works for you, the whole operation becomes very simple, since the command accepts multiple tables:
TRUNCATE rajeev1, rajeev2, rajeev3, ..
Dynamic DELETE
Else you need dynamic SQL like you already tried. The scary missing detail: you are completely open to SQL injection and catastrophic syntax errors. Use format() with %I (not %s to sanitize identifiers like table names. Or, better yet in this particular case, use an array of regclass as parameter instead:
CREATE OR REPLACE FUNCTION f_del_all(_tbls regclass)
RETURNS void AS
$func$
DECLARE
_tbl regclass;
BEGIN
FOREACH _tbl IN ARRAY _tbls LOOP
EXECUTE format('DELETE * FROM %s', _tbl);
END LOOP;
END
$func$ LANGUAGE plpgsql;
Call:
SELECT f_del_all('{rajeev1,rajeev2,rajeev3}');
Explanation here:
Table name as a PostgreSQL function parameter
You used wrong syntax for text array constant in the function call. But even if it was right, your function is not correct.
If your function has text array as argument you should loop over the array to execute query for each element.
CREATE OR REPLACE FUNCTION test (tablenames text[]) RETURNS int AS
$func$
DECLARE
tablename text;
BEGIN
FOREACH tablename IN ARRAY tablenames LOOP
EXECUTE FORMAT('delete * from %s', tablename);
END LOOP;
RETURN 1;
END
$func$ LANGUAGE plpgsql;
You can then call the function for several tables at once, not only for one.
SELECT test( '{rajeev1, rajeev2}' );
If you do not need this feature, simply change the argument type to text.
CREATE OR REPLACE FUNCTION test (tablename text) RETURNS int AS
$func$
BEGIN
EXECUTE format('delete * from %s', tablename);
RETURN 1;
END
$func$ LANGUAGE plpgsql;
SELECT test('rajeev1');
I recommend using the format function.
If you want to execute a function (say purge_this_one_table(tablename)) on a group of tables identified by similar names you can use this construction:
create or replace function purge_all_these_tables(mask text)
returns void language plpgsql
as $$
declare
tabname text;
begin
for tabname in
select relname
from pg_class
where relkind = 'r' and relname like mask
loop
execute format(
'purge_this_one_table(%s)',
tabname);
end loop;
end $$;
select purge_all_these_tables('agg_weekly_%');
It should be:
select test('{rajeev1}');
I am adjusting some PL/pgSQL code so my refcursor can take the table name as parameter. Therefore I changed the following line:
declare
pointCurs CURSOR FOR SELECT * from tableName for update;
with this one:
OPEN pointCurs FOR execute 'SELECT * FROM ' || quote_ident(tableName) for update;
I adjusted the loop, and voilà, the loop went through. Now at some point in the loop I needed to update the record (pointed by the cursor) and I got stuck. How should I properly adjust the following line of code?
UPDATE tableName set tp_id = pos where current of pointCurs;
I fixed the quotes for the tableName and pos and added the EXECUTE clause at the beginning, but I get the error on the where current of pointCurs.
Questions:
How can I update the record?
The function was working properly for tables from the public schema and failed for tables from other schemas (e.g., trace.myname).
Any comments are highly appreciated..
Answer for (i)
1. Explicit (unbound) cursor
EXECUTE is not a "clause", but a PL/pgSQL command to execute SQL strings. Cursors are not visible inside the command. You need to pass values to it.
Hence, you cannot use the special syntax WHERE CURRENT OFcursor. I use the system column ctid instead to determine the row without knowing the name of a unique column. Note that ctid is only guaranteed to be stable within the same transaction.
CREATE OR REPLACE FUNCTION f_curs1(_tbl text)
RETURNS void AS
$func$
DECLARE
_curs refcursor;
rec record;
BEGIN
OPEN _curs FOR EXECUTE 'SELECT * FROM ' || quote_ident(_tbl) FOR UPDATE;
LOOP
FETCH NEXT FROM _curs INTO rec;
EXIT WHEN rec IS NULL;
RAISE NOTICE '%', rec.tbl_id;
EXECUTE format('UPDATE %I SET tbl_id = tbl_id + 10 WHERE ctid = $1', _tbl)
USING rec.ctid;
END LOOP;
END
$func$ LANGUAGE plpgsql;
Why format() with %I?
There is also a variant of the FOR statement to loop through cursors, but it only works for bound cursors. We have to use an unbound cursor here.
2. Implicit cursor in FOR loop
There is normally no need for explicit cursors in plpgsql. Use the implicit cursor of a FOR loop instead:
CREATE OR REPLACE FUNCTION f_curs2(_tbl text)
RETURNS void AS
$func$
DECLARE
_ctid tid;
BEGIN
FOR _ctid IN EXECUTE 'SELECT ctid FROM ' || quote_ident(_tbl) FOR UPDATE
LOOP
EXECUTE format('UPDATE %I SET tbl_id = tbl_id + 100 WHERE ctid = $1', _tbl)
USING _ctid;
END LOOP;
END
$func$ LANGUAGE plpgsql;
3. Set based approach
Or better, yet (if possible!): Rethink your problem in terms of set-based operations and execute a single (dynamic) SQL command:
-- Set-base dynamic SQL
CREATE OR REPLACE FUNCTION f_nocurs(_tbl text)
RETURNS void AS
$func$
BEGIN
EXECUTE format('UPDATE %I SET tbl_id = tbl_id + 1000', _tbl);
-- add WHERE clause as needed
END
$func$ LANGUAGE plpgsql;
SQL Fiddle demonstrating all 3 variants.
Answer for (ii)
A schema-qualified table name like trace.myname actually consists of two identifiers. You have to
either pass and escape them separately,
or go with the more elegant approach of using a regclass type:
CREATE OR REPLACE FUNCTION f_nocurs(_tbl regclass)
RETURNS void AS
$func$
BEGIN
EXECUTE format('UPDATE %s SET tbl_id = tbl_id + 1000', _tbl);
END
$func$ LANGUAGE plpgsql;
I switched from %I to %s, because the regclass parameter is automatically properly escaped when (automatically) converted to text.
More details in this related answer:
Table name as a PostgreSQL function parameter
I would like to be able to get values of function variables whose names are queried from a table
Edited to show querying a table instead of query from static values:
create table __test__
(
_col text
);
insert into __test__
(_col)
values('_a');
create or replace function __test()
returns void
language 'plpgsql' as
$$
declare
_r record;
_a int;
_b int;
_sql text;
begin
_a = 1;
_b = 0;
for _r in select _col as _nam from __test__ a loop
-- query returns one row valued "_a"
_sql = 'select ' || _r._nam ;
execute _sql into _b;
end loop;
raise info 'value of _b %', _b;
end;
$$;
select __test()
when function executes so that _b = 1. Is it possible?
same error ...
ERROR: column "_a" does not exist
LINE 1: select _a
^
QUERY: select _a
CONTEXT: PL/pgSQL function "__test" line 15 at EXECUTE statement
You could create a temporary table, insert your variable names and values in it, and then execute a select against that. Just clean up after. I have used approaches like that before. It works ok. It does have extra overhead though.
Edit: adding an example
CREATE FUNCTION switch (in_var text) RETURNS text
LANGUAGE PLPGSQL VOLATILE AS $$
declare t_test text;
switch_vals text[];
BEGIN
CREATE TEMPORARY TABLE switch_values (var text, value text);
EXECUTE $e$ INSERT INTO switch_values VALUES
('a', '1'), ('b', '2'), ('c', '3') $e$;
EXECUTE $e$ SELECT value FROM switch_values WHERE var = $e$ || quote_literal(in_var)
INTO t_test;
DROP TABLE switch_values;
RETURN t_test;
END; $$;
postgres=# select switch('a');
switch
--------
1
(1 row)
Let's try to reframe the question: what you're after would be the equivalent of Perl eval()
function, with its ability to execute a dynamically generated piece of code for which "any outer lexical variables are visible to it". In your example, the variable would be _a, but as you can see from the error message, it can't be interpolated by a dynamic SQL statement. The reason is that the SQL interpreter has no visibility on the current pl/pgsql variables, or even the knowledge that such variables exist. They are confined to pl/pgsql.
What would be needed here is a context-aware dynamically-generated pl/pgsql statement, but this language does not have this feature. It's doubtful that a trick could be found to achieve the result without this feature. For all its ability to interface nicely with SQL, other than that it's a fairly static language.
On the other hand, this would be no problem for pl/perl.