I have the function:
test(IN _partition)
Inside my function I would like to append the '_partition' to the beginning of my table name.
FROM table_ + '_partition'
The end result:
select * from test(12345);
This function will query the table: table_12345
You need PL/PgSQL dynamic SQL with EXECUTE and the format function, e.g.
RETURN QUERY EXECUTE format('SELECT * FROM %I', _partition);
However, this is a mark of a design that will probably be painful to work with.
Have you looked at PostgreSQL's table inheritance features?
Related
I'm trying to EXECUTE some SELECTs to use inside a function, my code is something like this:
DECLARE
result_one record;
BEGIN
EXECUTE 'WITH Q1 AS
(
SELECT id
FROM table_two
INNER JOINs, WHERE, etc, ORDER BY... DESC
)
SELECT Q1.id
FROM Q1
WHERE, ORDER BY...DESC';
RETURN final_result;
END;
I know how to do it in MySQL, but in PostgreSQL I'm failing. What should I change or how should I do it?
For a function to be able to return multiple rows it has to be declared as returns table() (or returns setof)
And to actually return a result from within a PL/pgSQL function you need to use return query (as documented in the manual)
To build dynamic SQL in Postgres it is highly recommended to use the format() function to properly deal with identifiers (and to make the source easier to read).
So you need something like:
create or replace function get_data(p_sort_column text)
returns table (id integer)
as
$$
begin
return query execute
format(
'with q1 as (
select id
from table_two
join table_three on ...
)
select q1.id
from q1
order by %I desc', p_sort_column);
end;
$$
language plpgsql;
Note that the order by inside the CTE is pretty much useless if you are sorting the final query unless you use a LIMIT or distinct on () inside the query.
You can make your life even easier if you use another level of dollar quoting for the dynamic SQL:
create or replace function get_data(p_sort_column text)
returns table (id integer)
as
$$
begin
return query execute
format(
$query$
with q1 as (
select id
from table_two
join table_three on ...
)
select q1.id
from q1
order by %I desc
$query$, p_sort_column);
end;
$$
language plpgsql;
What a_horse said. And:
How to return result of a SELECT inside a function in PostgreSQL?
Plus, to pick a column for ORDER BY dynamically, you have to add that column to the SELECT list of your CTE, which leads to complications if the column can be duplicated (like with passing 'id') ...
Better yet, remove the CTE entirely. There is nothing in your question to warrant its use anyway. (Only use CTEs when needed in Postgres, they are typically slower than equivalent subqueries or simple queries.)
CREATE OR REPLACE FUNCTION get_data(p_sort_column text)
RETURNS TABLE (id integer) AS
$func$
BEGIN
RETURN QUERY EXECUTE format(
$q$
SELECT t2.id -- assuming you meant t2?
FROM table_two t2
JOIN table_three t3 on ...
ORDER BY t2.%I DESC NULL LAST -- see below!
$q$, $1);
END
$func$ LANGUAGE plpgsql;
I appended NULLS LAST - you'll probably want that, too:
PostgreSQL sort by datetime asc, null first?
If p_sort_column is from the same table all the time, hard-code that table name / alias in the ORDER BY clause. Else, pass the table name / alias separately and auto-quote them separately to be safe:
Define table and column names as arguments in a plpgsql function?
I suggest to table-qualify all column names in a bigger query with multiple joins (t2.id not just id). Avoids various kinds of surprising results / confusion / abuse.
And you may want to schema-qualify your table names (myschema.table_two) to avoid similar troubles when calling the function with a different search_path:
How does the search_path influence identifier resolution and the "current schema"
How can I write a dynamic SELECT INTO query inside a PL/pgSQL function in Postgres?
Say I have a variable called tb_name which is filled in a FOR loop from information_schema.tables. Now I have a variable called tc which will be taking the row count for each table. I want something like the following:
FOR tb_name in select table_name from information_schema.tables where table_schema='some_schema' and table_name like '%1%'
LOOP
EXECUTE FORMAT('select count(*) into' || tc 'from' || tb_name);
END LOOP
What should be the data type of tb_name and tc in this case?
CREATE OR REPLACE FUNCTION myfunc(_tbl_pattern text, _schema text = 'public')
RETURNS void AS -- or whatever you want to return
$func$
DECLARE
_tb_name information_schema.tables.table_name%TYPE; -- currently varchar
_tc bigint; -- count() returns bigint
BEGIN
FOR _tb_name IN
SELECT table_name
FROM information_schema.tables
WHERE table_schema = _schema
AND table_name ~ _tbl_pattern -- see below!
LOOP
EXECUTE format('SELECT count(*) FROM %I.%I', _schema, _tb_name)
INTO _tc;
-- do something with _tc
END LOOP;
END
$func$ LANGUAGE plpgsql;
Notes
I prepended all parameters and variables with an underscore (_) to avoid naming collisions with table columns. Just a useful convention.
_tc should be bigint, since that's what the aggregate function count() returns.
The data type of _tb_name is derived from its parent column dynamically: information_schema.tables.table_name%TYPE. See the chapter Copying Types in the manual.
Are you sure you only want tables listed in information_schema.tables? Makes sense, but be aware of implications. See:
How to check if a table exists in a given schema
a_horse already pointed to the manual and Andy provided a code example. This is how you assign a single row or value returned from a dynamic query with EXECUTE to a (row) variable. A single column (like count in the example) is decomposed from the row type automatically, so we can assign to the scalar variable tc directly - in the same way we would assign a whole row to a record or row variable. Related:
How to get the value of a dynamically generated field name in PL/pgSQL
Schema-qualify the table name in the dynamic query. There may be other tables of the same name in the current search_path, which would result in completely wrong (and very confusing!) results without schema-qualification. Sneaky bug! Or this schema is not in the search_path at all, which would make the function raise an exception immediately.
How does the search_path influence identifier resolution and the "current schema"
Always quote identifiers properly to defend against SQL injection and random errors. Schema and table have to be quoted separately! See:
Table name as a PostgreSQL function parameter
Truncating all tables in a Postgres database
I use the regular expression operator ~ in table_name ~ _tbl_pattern instead of table_name LIKE ('%' || _tbl_pattern || '%'), that's simpler. Be wary of special characters in the pattern parameter either way! See:
PostgreSQL Reverse LIKE
Escape function for regular expression or LIKE patterns
Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL
I set a default for the schema name in the function call: _schema text = 'public'. Just for convenience, you may or may not want that. See:
Assigning default value for type
Addressing your comment: to pass values, use the USING clause like:
EXECUTE format('SELECT count(*) FROM %I.%I
WHERE some_column = $1', _schema, _tb_name,column_name)
USING user_def_variable;
Related:
INSERT with dynamic table name in trigger function
It looks like you want the %I placeholder for FORMAT so that it treats your variable as an identifier. Also, the INTO clause should go outside the prepared statement.
FOR tb_name in select table_name from information_schema.tables where table_schema='some_schema' and table_name like '%1%'
LOOP
EXECUTE FORMAT('select count(*) from %I', tb_name) INTO tc;
END LOOP
I have my_table with two text columns: my_query, which contains various DML queries in text form; and and my_explanation, which is entirely populated with nulls.
I'd like to do something like:
UPDATE my_table SET my_explanation = execute explain analyze my_table.my_query
So that the my_explanation column on each row is updated to contain the textual output of the explain analyze of the query contained in its my_query column.
I tried making a function with cursors but it didn't work. I'm still learning pgplsql. Any ideas?
EXECUTE is a PL/pgSQL statement; it can't be used in an SQL query, only in a LANGUAGE plpgsql function or a DO block.
You probably want a function like this:
CREATE FUNCTION explain_query(sql TEXT) RETURNS SETOF TEXT AS $$
BEGIN
RETURN QUERY EXECUTE 'EXPLAIN ANALYZE ' || sql;
END
$$
LANGUAGE plpgsql;
Because EXPLAIN returns multiple rows, you'll need to aggregate the output to fit it into a single record in my_table:
UPDATE my_table
SET my_explanation = (
SELECT string_agg(plan, E'\n')
FROM explain_query(my_query) plan
)
I was attempting to use Dynamic SQL to run some queries in postgres.
Example:
EXECUTE format('SELECT * from result_%s_table', quote_ident((select id from ids where condition = some_condition)))
I have to query a table, which is of the form result_%s_table wherein, I need to substitute the correct table name (an id) from an another table.
I get the error ERROR: prepared statement "format" does not exist
Link: string substitution with query result postgresql
EXECUTE ... USING only works in PL/PgSQL - ie within functions or DO blocks written in the PL/PgSQL language. It does not work in plain SQL; the EXECUTE in plain SQL is completely different, for executing prepared statements. You cannot use dynamic SQL directly in PostgreSQL's SQL dialect.
Compare:
PL/PgSQL's EXECUTE ... USING; to
SQL's EXECUTE
See the 2nd last par in my prior answer.
In addition to not running except in PL/PgSQL your SQL statement is wrong, it won't do what you expect. If (select id from ids where condition = some_condition) returns say 42, the statement would fail if id is an integer. If it's cast to text you'd get:
EXECUTE format('SELECT * from result_%s_table', quote_ident('42'));
EXECUTE format('SELECT * from result_%s_table', '"42"');
EXECUTE 'SELECT * from result_"42"_table';
That's invalid. You actually want result_42_table or "result_42_table". You'd have to write something more like:
EXECUTE format('SELECT * from %s', quote_ident('result_'||(select id from ids where condition = some_condition)||'_table'))
... if you must use quote_ident.
CREATE OR REPLACE FUNCTION public.exec(
text)
RETURNS SETOF RECORD
LANGUAGE 'plpgsql'
AS $BODY$
BEGIN
RETURN QUERY EXECUTE $1 ;
END
$BODY$;
usage:
select * from exec('select now()') as t(dt timestamptz)
Try using
RETURN QUERY EXECUTE '<SQL Command>'
This will return data into form of table. You have to use this into stored function of PostgreSQL.
I have already created on full demonstration on custom filter and custom sorting using dynamic query of PostgreSQL.
Please visit this url:
http://www.dbrnd.com/2015/05/postgresql-dynamic-sql/
These all look more complicated than the OP's question. A different formatting should do the trick.. but it could absolutely the case that I don't understand.
From how I read OP's question, I think others in a similar situation may benefit from how I got it.
I am using Postgre on Redshift, and I ran into this issue and found a solution.
I was trying to create a dynamic query, putting in my own date.
date = dt.date(2018, 10, 30)
query = ''' select * from table where date >= ''' + str(my_date) + ''' order by date '''
But, the query entirely ignores the condition when typing it this way.
However, if you use the percent sign (%), you can insert the date correctly.
One correct way to write the above statement is:
query = ''' select * from table where date >= ''' + ''' '%s' ''' % my_date + ''' order by date '''
So, maybe this is helpful, or maybe it is not. I hope it helps at least one person in my situation!
Best wishes.
EXECUTE will work only on pl/pqsql environment.
instead of EXECUTE try with SELECT
SELECT format('SELECT * from result_%s_table', quote_ident((select id from ids where condition = some_condition))
output would be the dynamic query.
I want to use SELECT INTO to make a temporary table in one of my functions. SELECT INTO works in SQL but not PL/pgSQL.
This statement creates a table called mytable (If orig_table exists as a relation):
SELECT *
INTO TEMP TABLE mytable
FROM orig_table;
But put this function into PostgreSQL, and you get the error: ERROR: "temp" is not a known variable
CREATE OR REPLACE FUNCTION whatever()
RETURNS void AS $$
BEGIN
SELECT *
INTO TEMP TABLE mytable
FROM orig_table;
END; $$ LANGUAGE plpgsql;
I can SELECT INTO a variable of type record within PL/pgSQL, but then I have to define the structure when getting data out of that record. SELECT INTO is really simple - automatically creating a table of the same structure of the SELECT query. Does anyone have any explanation for why this doesn't work inside a function?
It seems like SELECT INTO works differently in PL/pgSQL, because you can select into the variables you've declared. I don't want to declare my temporary table structure, though. I wish it would just create the structure automatically like it does in SQL.
Try
CREATE TEMP TABLE mytable AS
SELECT *
FROM orig_table;
Per http://www.postgresql.org/docs/current/static/sql-selectinto.html
CREATE TABLE AS is functionally similar to SELECT INTO. CREATE TABLE AS is the recommended syntax, since this form of SELECT INTO is not available in ECPG or PL/pgSQL, because they interpret the INTO clause differently. Furthermore, CREATE TABLE AS offers a superset of the functionality provided by SELECT INTO.