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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;

Each declaration and each statement within a block is terminated by a semicolon.

All key words and identifiers can be written in mixed upper and lower case. Identifiers are implicitly converted to lower-case 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 transactions, since PostgreSQL does not have nested transactions.

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