支持38.2. 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 [ 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. Tip A common mistake is to write a semicolon immediately after BEGIN. This is incorrect and will result in a syntax error. A label is only needed if you want to identify the block for use in an EXIT statement, or to qualify the names of the variables declared in the block. If a label is given after END, it must match the label at the block's beginning. All key words are case-insensitive. Identifiers are implicitly converted to lowercase unless double-quoted, just as they are in ordinary SQL commands. 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 nest, just as in ordinary SQL. 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. Variables declared in a subblock mask any similarly-named variables of outer blocks for the duration of the subblock; but you can access the outer variables anyway if you qualify their names with their block's label. For example: CREATE FUNCTION somefunc() RETURNS integer AS $$ << outerblock >> DECLARE quantity integer := 30; BEGIN RAISE NOTICE 'Quantity here is %', quantity; -- Prints 30 quantity := 50; -- -- Create a subblock -- DECLARE quantity integer := 80; BEGIN RAISE NOTICE 'Quantity here is %', quantity; -- Prints 80 RAISE NOTICE 'Outer quantity here is %', outerblock.quantity; -- Prints 50 END; RAISE NOTICE 'Quantity here is %', quantity; -- Prints 50 RETURN quantity; END; $$ LANGUAGE plpgsql;Note There is actually a hidden “outer block” surrounding the body of any PL/pgSQL function. This block provides the declarations of the function's parameters (if any), as well as some special variables such as FOUND (see Section 38.5.5, “Obtaining the Result Status”). The outer block is labeled with the function's name, meaning that parameters and special variables can be qualified with the function's name. It is important not to confuse the use of BEGIN/END for grouping statements in PL/pgSQL with the similarly-named SQL 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 38.6.5, “Trapping Errors”.
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. Tip
A common mistake is to write a semicolon immediately after BEGIN. This is incorrect and will result in a syntax error. A label is only needed if you want to identify the block for use in an EXIT statement, or to qualify the names of the variables declared in the block. If a label is given after END, it must match the label at the block's beginning. All key words are case-insensitive. Identifiers are implicitly converted to lowercase unless double-quoted, just as they are in ordinary SQL commands. 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 nest, just as in ordinary SQL. 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. Variables declared in a subblock mask any similarly-named variables of outer blocks for the duration of the subblock; but you can access the outer variables anyway if you qualify their names with their block's label. For example: CREATE FUNCTION somefunc() RETURNS integer AS $$
<< outerblock >>
DECLARE
quantity integer := 30;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 30
quantity := 50;
--
-- Create a subblock
--
DECLARE
quantity integer := 80;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 80
RAISE NOTICE 'Outer quantity here is %', outerblock.quantity; -- Prints 50
END; RAISE NOTICE 'Quantity here is %', quantity; -- Prints 50 RETURN quantity;
END;
$$ LANGUAGE plpgsql;Note
There is actually a hidden “outer block” surrounding the body of any PL/pgSQL function. This block provides the declarations of the function's parameters (if any), as well as some special variables such as FOUND (see Section 38.5.5, “Obtaining the Result Status”). The outer block is labeled with the function's name, meaning that parameters and special variables can be qualified with the function's name. It is important not to confuse the use of BEGIN/END for grouping statements in PL/pgSQL with the similarly-named SQL 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 38.6.5, “Trapping Errors”.