REPEAT#
Примечание
Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.
Synopsis#
[label :] REPEAT
statements
UNTIL condition
END REPEAT
Description#
The REPEAT UNTIL statement is an optional construct in SQL
routines to allow processing of a block of statements
as long as a condition is met. The condition is validated as a last step of each
iteration.
The block of statements is processed at least once. After the first, and every
subsequent processing the expression condidtion is validated. If the result is
true, processing moves to END REPEAT and continues with the next statement in
the function. If the result is false, the statements are processed again.
The optional label before the REPEAT keyword can be used to name the
block.
Note that a WHILE statement is very similar, with the difference that for
REPEAT the statements are processed at least once, and for WHILE blocks the
statements might not be processed at all.
Examples#
The following routine shows a routine with a REPEAT statement that runs until
the value of a is greater or equal to 10.
FUNCTION test_repeat(a bigint)
RETURNS bigint
BEGIN
REPEAT
SET a = a + 1;
UNTIL a >= 10
END REPEAT;
RETURN a;
END
Since a is also the input value and it is increased before the check the
routine always returns 10 for input values of 9 or less, and the input value
1 for all higher values.
Following are a couple of example invocations with result and explanation:
SELECT test_repeat(5); -- 10
SELECT test_repeat(9); -- 10
SELECT test_repeat(10); -- 11
SELECT test_repeat(11); -- 12
SELECT test_repeat(12); -- 13
Further examples of varying complexity that cover usage of the REPEAT
statement in combination with other statements are available in the SQL
routines examples documentation.