Store query result in a variable using in PL/pgSQL

Question

How to assign the result of a query to a variable in PL/pgSQL, the procedural language of PostgreSQL?

I have a function:

CREATE OR REPLACE FUNCTION test(x numeric)
RETURNS character varying AS
$BODY$
DECLARE
name   character varying(255);
begin
 name ='SELECT name FROM test_table where id='||x;
  
 if(name='test')then
  --do somthing
 else
  --do the else part
 end if;
end;
return -- return my process result here
$BODY$
LANGUAGE plpgsql VOLATILE

In the above function I need to store the result of this query:

'SELECT name FROM test_table where id='||x;

to the variable name.

How to process this?

Catacaustic

Answer 1

I think you're looking for SELECT select_expressions INTO:

select test_table.name into name from test_table where id = x;

That will pull the name from test_table where id is your function's argument and leave it in the name variable. Don't leave out the table name prefix on test_table.name or you'll get complaints about an ambiguous reference.

Alecto

What if I need multiple variables. Like select test_table.name, test_table.id, test_table.ssn? – Prokofiev

@DaoLam: From the documentation I liked to: "The result of a SQL command yielding a single row (possibly of multiple columns) can be assigned to a record variable, row-type variable, or list of scalar variables." – Alecto

@muistooshort so you're saying i can do the same and i can use name.id, name.ssn to retrieve? I tried it with IF EXISTS but didn't work: IF EXISTS (select * into name from test_table...)) – Prokofiev

@DaoLam Why are you combining INTO with IF EXISTS? Maybe you should ask a new question so that you can explain what you're trying to do. – Alecto

@muistooshort Thank you! My question is here: #28887330 – Prokofiev

@muistooshort this way is not working when the query is returning an array. Is there an alternative to this in case of arrays? Here is my question on the same : #34195318 – Salvia

Note the ability to add TEMPORARY before the table name to create a temporary table. (Else, one may want to use a DROP TABLE IF EXISTS test_table; and keep an eye out for unnecessary tables.) – Bayreuth

There is no example in documentation (or I missed it), but as @muistooshort noted, you can select into multiple variables with single select: SELECT test_table.column1, test_table.column2 INTO variable1, variable2 FROM test_table WHERE id = x; – Glorianna

Just FYI I just found out that in my old version of Postgres that NONE of these solutions work if followed by a Dynamic Query. If your main query is dynamic, you have to make the first query dynamic also using EXECUTE .... INTO variable. This took me a looong time to figure out. – Miquelmiquela

The Postgres docs refer to this syntax as SELECT select_expressions INTO (which does not create a table), not SELECT INTO (which does). More info – Glace

Answer 2

To assign a single variable, you can also use plain assignment in a PL/pgSQL code block, with a scalar subquery to the right:

name := (SELECT t.name from test_table t where t.id = x);

Effectively the same as SELECT INTO like @mu already provided, with subtle differences:

• SELECT INTO is slightly faster in my tests on Postgres 14.
  (Plain assignment of a constant, without involving SELECT, is 10x faster, still.)
• SELECT INTO also sets the special variable FOUND, while plain assignment does not. You may want one or the other.
• SELECT INTO can also assign multiple variables at once. See:
  • SELECT INTO with more than one attribution

Notably, this works, too:

name := t.name from test_table t where t.id = x;

A SELECT statement without leading SELECT. But I would not use this hybrid. Better use one of the first two, clearer, documented methods, as @Pavel commented.

Ngocnguyen

This is not good idea - this feature is not documented and it is ugly – Wellborn

PL/pgSQL allows mix of SQL and PL - and sometimes you can create really strange creatures, but is better mix PL and SQL cleanly - in isolated statements. – Wellborn

@PavelStehule: I agree, your form is preferable. – Ngocnguyen

Actually i do prefere your syntax, but the problem is when you wana handle errors, your statement doesnt send FOUND to true in the opposite of the select into statement, checkout (postgresql.org/docs/9.1/plpgsql-statements.html) – Aholla

Answer 3

The usual pattern is EXISTS(subselect):

BEGIN
  IF EXISTS(SELECT name
              FROM test_table t
             WHERE t.id = x
               AND t.name = 'test')
  THEN
     ---
  ELSE
     ---
  END IF;

This pattern is used in PL/SQL, PL/pgSQL, SQL/PSM, ...

Wellborn

Answer 4

Create Learning Table:

CREATE TABLE "public"."learning" (
    "api_id" int4 DEFAULT nextval('share_api_api_id_seq'::regclass) NOT NULL,
    "title" varchar(255) COLLATE "default"
);

Insert Data Learning Table:

INSERT INTO "public"."learning" VALUES ('1', 'Google AI-01');
INSERT INTO "public"."learning" VALUES ('2', 'Google AI-02');
INSERT INTO "public"."learning" VALUES ('3', 'Google AI-01');

Step: 01

CREATE OR REPLACE FUNCTION get_all (pattern VARCHAR) RETURNS TABLE (
        learn_id INT,
        learn_title VARCHAR
) AS $$
BEGIN
    RETURN QUERY SELECT
        api_id,
        title
    FROM
        learning
    WHERE
        title = pattern ;
END ; $$ LANGUAGE 'plpgsql';

Step: 02

SELECT * FROM get_all('Google AI-01');

Step: 03

DROP FUNCTION get_all();

Demo:

Aeneus

Answer 5

Per Executing a Query with a Single-Row Result, use this syntax:

SELECT select_expressions INTO [STRICT] target FROM ...

where target can be a record variable, a row variable, or a comma-separated list of simple variables and record/row fields.

Unlike the SELECT INTO, SELECT select_expressions INTO does not create a table.

In your example, you have a single simple variable name, so the select statement would be:

SELECT test_table.name INTO name FROM test_table WHERE test_table.id = x;

Glace

Answer 6

Many answers here omit important parts of using functions, and given the popularity I think many arrive here looking for a quick overall primer on using functions.

Here's an example of using functions in postgres (including declaration, variables, args, return values, and running). Below is an over-baked way of updating the tweet on the bottom right "blurb" with "hello world".

id (serial)	pub_id (text)	tweet (text)
1	abc	hello world
2	def	blurb

-- Optional drop if replace fails below.
drop function if exists sync_tweets(text, text);

create or replace function sync_tweets(
    src_pub_id text, -- function arguments
    dst_pub_id text
) returns setof tweets as -- i.e. rows. int, text work too
$$
declare
    src_id    int; -- temp function variables (not args)
    dest_id   int;
    src_tweet text;
begin
    -- query result into a temp variable
    src_id := (select id from tweets where pub_id = src_pub_id);

    -- query result into a temp variable (another way)
    select tweet into src_tweet from tweets where id = src_id;

    dest_id := (select id from tweets where pub_id = dst_pub_id);
    update tweets set tweet=src_tweet where id = dest_id;

    return query -- i.e. rows, return 0 with return int above works too
        select * from tweets where pub_id in (src_pub_id, dst_pub_id);
end
$$ language plpgsql; -- need the language to avoid ERROR 42P13

-- Run it!
select * from sync_tweets('abc', 'def');

/*
  Outputs
   __________________________________________________ 
  |  id (serial)  |  pub_id (text)  |  tweet (text)  |
  |---------------|-----------------|----------------|
  |  1            |  abc            |  hello world   |
  |  2            |  def            |  blurb         |
  --------------------------------------------------
*/

Gateway

Answer 7

For example, you create person table, then insert 2 rows into it as shown below as shown below:

CREATE TABLE person (
  id INT,
  name VARCHAR(20)
);

INSERT INTO person (id, name) VALUES (1, 'John'), (2, 'David');

Then, you can create my_func() which can store a query result into person_name, then return it as shown below:

CREATE FUNCTION my_func()
RETURNS VARCHAR(20)
AS $$
DECLARE
  person_id public.person.id%TYPE := 2;
  person_name public.person.name%TYPE;
BEGIN
  SELECT name INTO person_name FROM person WHERE id = person_id;
  RETURN person_name;
END;
$$ LANGUAGE plpgsql;

Then, calling my_func() returns David as shown below:

postgres=# SELECT my_func();
 my_func
---------
 David
(1 row)

And, you can create my_func() which can store a query result into person_row, then return it as shown below:

CREATE FUNCTION my_func()
RETURNS person
AS $$
DECLARE
  person_row public.person%ROWTYPE; -- Here
  -- person_row RECORD; -- Here
BEGIN
  SELECT * INTO person_row FROM person WHERE id = 2;
  RETURN person_row;
END;
$$ LANGUAGE plpgsql;

Then, calling my_func() returns a row as shown below:

postgres=# SELECT my_func();
  my_func
-----------
 (2,David)
(1 row)

Mouseear

Answer 8

You can use the following example to store a query result in a variable using PL/pgSQL:

 select * into demo from maintenanceactivitytrack ; 
    raise notice'p_maintenanceid:%',demo;

Sidhu