37.3. 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 [ label ];

Each declaration and each statement within a block is terminated by a semicolon. A block that appears within another block must have a semicolon after END , as shown above; however the final END that concludes a function body does not require a semicolon.

All key words and identifiers can be written in mixed upper and lower case. Identifiers are implicitly converted to lowercase unless double-quoted.

There are two types of comments in PL/pgSQL . A double dash ( -- ) starts a comment that extends to the end of the line. A /* starts a block comment that extends to the next occurrence of */ . Block comments cannot be nested, but double dash comments can be enclosed into a block comment and a double dash can hide the block comment delimiters /* and */ .

Any statement in the statement section of a block can be a subblock . Subblocks 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 $$ DECLARE quantity integer := 30; BEGIN RAISE NOTICE 'Quantity here is %', quantity; -- Quantity here is 30 quantity := 50; -- -- Create a subblock -- DECLARE quantity integer := 80; BEGIN RAISE NOTICE 'Quantity here is %', quantity; -- Quantity here is 80 END; RAISE NOTICE 'Quantity here is %', quantity; -- Quantity here is 50 RETURN quantity; END; $$ 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 that transaction, since there would be no context for them to execute in. However, a block containing an EXCEPTION clause effectively forms a subtransaction that can be rolled back without affecting the outer transaction. For more about that see Section 37.7.5 .