PL/pgSQL is a block-structured language. The complete text of a function definition must be a block. A block is defined as:
[ <<label
>> ] [ DECLAREdeclarations
] BEGINstatements
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, “Trapping Errors”.