Official PostgreSQL 8.3 PL/pgSQL Documentation URL: http://www.postgresql.org/docs/8.3/static/plpgsql.html
We cover only a subset of what we feel are the most useful constructs that we could squash in a single cheatsheet page
commonly used   1 New in this release.
FUNCTION CACHING
IMMUTABLE
STABLE
VOLATILE
CONTROL FLOW
FOR i IN 1 ... numtimes LOOP 
 statements 
END LOOP;

FOR i IN REVERSE numtimes ... 1 LOOP
 statements
END LOOP;

FOR var_e IN EXECUTE('somedynamicsql') LOOP 
 statements
 RETURN NEXT var_e;
END LOOP;

FOR var_e IN somesql LOOP 
 statements
 RETURN NEXT var_e;
END LOOP;

IF condition THEN
  :
END IF;

IF condition THEN
  :
ELSE
  :
END IF;

IF condition. THEN
  :
ELSIF condition THEN
  :
ELSE
  :
END IF;

WHILE condition LOOP
  :
END LOOP;

LOOP
 -- some computations
 EXIT WHEN count > 100;
 CONTINUE WHEN count < 50;
 -- some computations for count IN [50 .. 100] 
END LOOP;
RETURN constructs
RETURN somevariable
RETURN NEXT rowvariable
RETURN QUERY 1
RAISE FAMILY
RAISE DEBUG[1-5] 
RAISE EXCEPTION 
RAISE INFO 
RAISE LOG
RAISE NOTICE
EXCEPTION Handling
RAISE EXCEPTION 'Exception notice: %', var
EXCEPTION 
 WHEN condition THEN
	do something or 
	leave blank to ignore
END;
COMMON States and ERROR constants
FOUND
ROW_COUNT
division_by_zero
no_data_found
too_many_rows
unique_violation
Variable Setting
DECLARE
 somevar sometype :=  somevalue;
 somevar sometype
 curs1 refcursor;
 curs2 CURSOR FOR SELECT * FROM sometable;
 
somevar := somevalue

SELECT field1, field2
INTO somevar1, somevar2
FROM sometable WHERE .. LIMIT 1;
Return types
RETURNS somedatatype
RETURNS SETOF somedatatype
RETURNS refcursor
RETURNS trigger
RETURNS void
QUALIFIERS
SECURITY DEFINER
STRICT
COST cost_metric 1
ROWS est_num_rows 1

PLPGSQL FUNCTION SAMPLES

CREATE OR REPLACE FUNCTION fn_test(param_arg1 integer, param_arg2 text)
  RETURNS text AS
$$
DECLARE 
	var_a integer := 0;
	var_b text := 'test test test';
BEGIN
	RAISE NOTICE 'Pointless example to demonstrate a point';
	RETURN var_b || ' - ' || 
		CAST(param_arg1 As text) || ' - ' 
		|| param_arg2;
END
$$
  LANGUAGE 'plpgsql' STABLE;
  
SELECT fn_test(10, 'test');

--Example to RETURN QUERY --
CREATE OR REPLACE FUNCTION fnpgsql_get_peoplebylname_key(param_lname text)
  RETURNS SETOF int AS
$$
BEGIN
    RETURN QUERY SELECT name_key 
        FROM people WHERE last_name LIKE param_lname;
END
$$
  LANGUAGE 'plpgsql' STABLE;  
--Example using dynamic query --
CREATE OR REPLACE FUNCTION cp_addtextfield(param_schema_name text, param_table_name text, 
	param_column_name text)
  RETURNS text AS
  $$
  BEGIN
	EXECUTE 'ALTER TABLE ' ||
		quote_ident(param_schema_name) || '.' || quote_ident(param_table_name)
		|| ' ADD COLUMN ' || quote_ident(param_column_name) || ' text ';
	RETURN 'done';
  END; 
$$
  LANGUAGE 'plpgsql' VOLATILE;
  SELECT cp_addtextfield('public', 'employees', 'resume');
 
--Perform action --
 CREATE OR REPLACE FUNCTION cp_updatesometable(param_id bigint,
	param_lname varchar(50), param_fname varchar(50))
  RETURNS void AS
$$
BEGIN
   UPDATE people SET first_name = param_fname, last_name = param_lname 
	 WHERE name_key = param_id;
END;
$$
  LANGUAGE 'plpgsql' VOLATILE SECURITY DEFINER;
 
 --Sample logging trigger taken from docs
 CREATE TABLE emp_audit( 
    operation         char(1)   NOT NULL,
    stamp             timestamp NOT NULL,
    userid            text      NOT NULL,
    empname           text      NOT NULL,
    salary integer
);
 CREATE OR REPLACE FUNCTION process_emp_audit() RETURNS TRIGGER AS $$
    BEGIN
        -- Create a row in emp_audit to reflect the operation performed on emp,
        -- make use of the special variable TG_OP to work out the operation.
        IF (TG_OP = 'DELETE') THEN
            INSERT INTO emp_audit SELECT 'D', now(), current_user, OLD.*;
            RETURN OLD;
        ELSIF (TG_OP = 'UPDATE') THEN
            INSERT INTO emp_audit SELECT 'U', now(), current_user, NEW.*;
            RETURN NEW;
        ELSIF (TG_OP = 'INSERT') THEN
            INSERT INTO emp_audit SELECT 'I', now(), current_user, NEW.*;
            RETURN NEW;
        END IF;
        RETURN NULL; -- result is ignored since this is an AFTER trigger
    END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER emp_audit
AFTER INSERT OR UPDATE OR DELETE ON emp
    FOR EACH ROW EXECUTE PROCEDURE process_emp_audit();
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