How do you use variables in a simple PostgreSQL script? - postgresql

Question

For example, in MS-SQL, you can open up a query window and run the following:
DECLARE #List AS VARCHAR(8)
SELECT #List = 'foobar'
SELECT *
FROM dbo.PubLists
WHERE Name = #List
How is this done in PostgreSQL? Can it be done?

Answer 1

Complete answer is located in the official PostgreSQL documentation.
You can use new PG9.0 anonymous code block feature (http://www.postgresql.org/docs/9.1/static/sql-do.html )
DO $$
DECLARE v_List TEXT;
BEGIN
v_List := 'foobar' ;
SELECT *
FROM dbo.PubLists
WHERE Name = v_List;
-- ...
END $$;
Also you can get the last insert id:
DO $$
DECLARE lastid bigint;
BEGIN
INSERT INTO test (name) VALUES ('Test Name')
RETURNING id INTO lastid;
SELECT * FROM test WHERE id = lastid;
END $$;

Answer 2

DO $$
DECLARE
a integer := 10;
b integer := 20;
c integer;
BEGIN
c := a + b;
RAISE NOTICE'Value of c: %', c;
END $$;

Answer 3

You can use:
\set list '''foobar'''
SELECT * FROM dbo.PubLists WHERE name = :list;
That will do

Answer 4

Here's an example of using a variable in plpgsql:
create table test (id int);
insert into test values (1);
insert into test values (2);
insert into test values (3);
create function test_fn() returns int as $$
declare val int := 2;
begin
return (SELECT id FROM test WHERE id = val);
end;
$$ LANGUAGE plpgsql;
SELECT * FROM test_fn();
test_fn
---------
2
Have a look at the plpgsql docs for more information.

Answer 5

I've came across some other documents which they use \set to declare scripting variable but the value is seems to be like constant value and I'm finding for way that can be acts like a variable not a constant variable.
Ex:
\set Comm 150
select sal, sal+:Comm from emp
Here sal is the value that is present in the table 'emp' and comm is the constant value.

Answer 6

Building on #nad2000's answer and #Pavel's answer here, this is where I ended up for my Flyway migration scripts. Handling for scenarios where the database schema was manually modified.
DO $$
BEGIN
IF NOT EXISTS(
SELECT TRUE FROM pg_attribute
WHERE attrelid = (
SELECT c.oid
FROM pg_class c
JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE
n.nspname = CURRENT_SCHEMA()
AND c.relname = 'device_ip_lookups'
)
AND attname = 'active_date'
AND NOT attisdropped
AND attnum > 0
)
THEN
RAISE NOTICE 'ADDING COLUMN';
ALTER TABLE device_ip_lookups
ADD COLUMN active_date TIMESTAMP;
ELSE
RAISE NOTICE 'SKIPPING, COLUMN ALREADY EXISTS';
END IF;
END $$;

Answer 7

For use variables in for example alter table:
DO $$
DECLARE name_pk VARCHAR(200);
BEGIN
select constraint_name
from information_schema.table_constraints
where table_schema = 'schema_name'
and table_name = 'table_name'
and constraint_type = 'PRIMARY KEY' INTO name_pk;
IF (name_pk := '') THEN
EXECUTE 'ALTER TABLE schema_name.table_name DROP CONSTRAINT ' || name_pk;

Answer 8

Postgresql does not have bare variables, you could use a temporary table.
variables are only available in code blocks or as a user-interface feature.
If you need a bare variable you could use a temporary table:
CREATE TEMP TABLE list AS VALUES ('foobar');
SELECT dbo.PubLists.*
FROM dbo.PubLists,list
WHERE Name = list.column1;

Answer 9

I had to do something like this
CREATE OR REPLACE FUNCTION MYFUNC()
RETURNS VOID AS $$
DO
$do$
BEGIN
DECLARE
myvar int;
...
END
$do$
$$ LANGUAGE SQL;

Answer 10

You can also simply make a constant query that you use in the actual query:
WITH vars as (SELECT 'foobar' AS list)
SELECT *
FROM dbo.PubLists, vars
WHERE Name = vars.list

Answer 11

Given the popularity, and somewhat incomplete answers I'll provide two solutions.
A do block that won't return rows. You can return rows with a transaction cursor, but it's a bit messy.
A function (that returns rows)
Below I'll use an over-baked example 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
A simple do block
do $$
declare
src_pub_id text;
dst_pub_id text;
src_id int;
dest_id int;
src_tweet text;
begin
src_pub_id := 'abc';
dst_pub_id := 'def';
-- query result into a temp variable
src_id := (select id from tweets where pub_id = src_pub_id);
-- query result into a temp variable (another way)
select tweet into src_tweet from tweets where id = src_id;
dest_id := (select id from tweets where pub_id = dst_pub_id);
update tweets set tweet=src_tweet where id = dest_id;
end $$ language plpgsql; -- need the language to avoid ERROR 42P13
A function
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');
-- Optional drop if you don't want the db to keep your function
drop function if exists sync_tweets(text, text);
/*
Outputs
__________________________________________________
| id (serial) | pub_id (text) | tweet (text) |
|---------------|-----------------|----------------|
| 1 | abc | hello world |
| 2 | def | blurb |
--------------------------------------------------
*/