FOR

A FOR loop repeats a sequence of steps a specific number of times. The number of times might be specified by the user, or might be specified by the number of rows in a cursor. The syntax of these two types of FOR loops is slightly different.

For more information on loops, see Working with Loops.

See also

BREAK, CONTINUE

Syntax

To loop over all rows in a cursor, use:

FOR <row_variable> IN <cursor_name> DO
    statement;
    [ statement; ... ]
END FOR [ <label> ] ;

To loop a specified number of times, use:

FOR <counter_variable> IN [ REVERSE ] <start> TO <end> { DO | LOOP }
    statement;
    [ statement; ... ]
END { FOR | LOOP } [ <label> ] ;

Where:

row_variable

Specify a variable name that follows the rules for Object Identifiers.

Do not add a declaration for this variable in the DECLARE or BEGIN … END sections. The name should not already be defined in the scope of the local block.

The name is valid inside the FOR loop, but not outside the FOR loop.

The row_variable holds one row from the cursor. Fields within that row are accessed using dot notation. For example:

my_row_variable.my_column_name

A more complete example is included in the examples below.

counter_variable

Specify a variable name that follows the rules for Object Identifiers.

The name of the counter_variable is valid only inside the FOR loop. If a variable with the same name is declared outside the loop, the outer variable and the loop variable are separate. Inside the loop, references to that name are resolved to the loop variable.

The code inside the FOR loop is allowed to read the value of the counter variable, but should not change it. For example, do not increment the counter variable manually to change the step size.

start

This is the initial value of counter_variable.

The starting value should be an INTEGER or an expression that evaluates to an INTEGER.

end

This is the final value of counter_variable, after the counter_variable has been incremented as you loop.

The ending value should be an INTEGER or an expression that evaluates to an INTEGER.

The end value should be greater than or equal to the start value. If end is less than start, the loop executes 0 times (even if the REVERSE keyword is used).

statement

A statement can be any of the following:

  • A single SQL statement (including CALL).

  • A control-flow statement (e.g. looping or branching statement).

  • A nested block.

cursor_name

The name of the cursor to iterate through.

label

An optional label. Such a label can be a jump target for a BREAK or CONTINUE statement. A label must follow the naming rules for Object Identifiers.

Usage Notes

  • The loop iterates up to and including the end point.

    For example, FOR i IN 1 TO 10 loops 10 times, and during the final iteration the value of i is 10.

    If you use the REVERSE keyword, then the loop iterates backwards down to and including the start value.

  • A loop can contain multiple statements. You can use, but are not required to use, a BEGIN … END block to contain those statements.

  • The optional keyword REVERSE causes Snowflake to start with the end value and decrement down to the start value.

  • Although you can change the value of the counter_variable inside the loop, Snowflake recommends that you avoid doing this. Changing the value makes the code more difficult to understand.

  • If you use the keyword DO, then use END FOR at the end of the FOR loop. If you use the keyword LOOP, then use END LOOP at the end of the FOR loop.

Examples

Cursor-Based FOR Loops

This example shows how to use a cursor to sum the values in the price column of all the rows returned by a query. This stored procedure behaves somewhat like an aggregate function.

CREATE or replace TABLE invoices (price NUMBER(12, 2));
INSERT INTO invoices (price) VALUES
    (11.11),
    (22.22);
CREATE OR REPLACE PROCEDURE for_loop_over_cursor()
RETURNS FLOAT
LANGUAGE SQL
AS
$$
DECLARE
    total_price FLOAT;
    c1 CURSOR FOR SELECT price FROM invoices;
BEGIN
    total_price := 0.0;
    OPEN c1;
    FOR rec IN c1 DO
        total_price := total_price + rec.price;
    END FOR;
    CLOSE c1;
    RETURN total_price;
END;
$$
;

Here is the output of the stored procedure:

CALL for_loop_over_cursor();
+----------------------+
| FOR_LOOP_OVER_CURSOR |
|----------------------|
|                33.33 |
+----------------------+
Counter-Based FOR Loops

This example shows how to use a FOR loop to iterate a specified number of times:

CREATE PROCEDURE simple_for(iteration_limit INTEGER)
RETURNS INTEGER
LANGUAGE SQL
AS
$$
    DECLARE
        counter INTEGER DEFAULT 0;
    BEGIN
        FOR i IN 1 TO iteration_limit DO
            counter := counter + 1;
        END FOR;
        RETURN counter;
    END;
$$;

Here is the output of the stored procedure:

CALL simple_for(3);
+------------+
| SIMPLE_FOR |
|------------|
|          3 |
+------------+

The following example shows how to use the REVERSE keyword to count backwards.

CREATE PROCEDURE reverse_loop(iteration_limit INTEGER)
RETURNS VARCHAR
LANGUAGE SQL
AS
$$
    DECLARE
        values_of_i VARCHAR DEFAULT '';
    BEGIN
        FOR i IN REVERSE 1 TO iteration_limit DO
            values_of_i := values_of_i || ' ' || i::varchar;
        END FOR;
        RETURN values_of_i;
    END;
$$;

Here is the output of the stored procedure:

CALL reverse_loop(3);
+--------------+
| REVERSE_LOOP |
|--------------|
|  3 2 1       |
+--------------+

The following example shows the behavior when the loop counter variable has the same name (i) as a variable that was already declared. Within the FOR loop, references to i resolve to the loop counter variable (not to the variable declared outside of the loop).

CREATE PROCEDURE p(iteration_limit INTEGER)
RETURNS VARCHAR
LANGUAGE SQL
AS
$$
    DECLARE
        counter INTEGER DEFAULT 0;
        i INTEGER DEFAULT -999;
        return_value VARCHAR DEFAULT '';
    BEGIN
        FOR i IN 1 TO iteration_limit DO
            counter := counter + 1;
        END FOR;
        return_value := 'counter: ' || counter::varchar || '\n';
        return_value := return_value || 'i: ' || i::VARCHAR;
        RETURN return_value;
    END;
$$;

Here is the output of the stored procedure:

CALL p(3);
+------------+
| P          |
|------------|
| counter: 3 |
| i: -999    |
+------------+
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