19.2. Structure of PL/pgSQL

PL/pgSQL is a block structured language. The complete text of a function definition must be a block. A block is defined as:

[ <<label>> ]
[ DECLARE
    declarations ]
BEGIN
    statements
END;

Any statement in the statement section of a block can be a sub-block. Sub-blocks can be used for logical grouping or to localize variables to a small group of statements.

The variables declared in the declarations section preceding a block are initialized to their default values every time the block is entered, not only once per function call. For example:

CREATE FUNCTION somefunc() RETURNS INTEGER AS '
DECLARE
   quantity INTEGER := 30;
BEGIN
   RAISE NOTICE ''Quantity here is %'',quantity;  -- Quantity here is 30
   quantity := 50;
   --
   -- Create a sub-block
   --
   DECLARE
      quantity INTEGER := 80;
   BEGIN
      RAISE NOTICE ''Quantity here is %'',quantity;  -- Quantity here is 80
   END;

   RAISE NOTICE ''Quantity here is %'',quantity;  -- Quantity here is 50

   RETURN quantity;
END;
' LANGUAGE 'plpgsql';

It is important not to confuse the use of BEGIN/END for grouping statements in PL/pgSQL with the database commands for transaction control. PL/pgSQL's BEGIN/END are only for grouping; they do not start or end a transaction. Functions and trigger procedures are always executed within a transaction established by an outer query --- they cannot start or commit transactions, since PostgreSQL does not have nested transactions.