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debugging-statements.md

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Debugging statements

ZetaSQL supports the following debugging statements.

ASSERT

ASSERT expression [AS description]

Description

Evaluates expression.

If expression evaluates to TRUE, the statement returns successfully without any result.

If expression evaluates to FALSE or NULL, the statement generates an error. If AS description is present, description will appear in the error message.

expression must evaluate to a BOOL.

description must be a STRING literal.

Examples

The following examples assert that the data source contains more than a specific number of rows.

-- This query succeeds and no error is produced.
ASSERT (
  (SELECT COUNT(*) > 5 FROM UNNEST([1, 2, 3, 4, 5, 6]))
) AS 'Table must contain more than 5 rows.';
-- Error: Table must contain more than 10 rows.
ASSERT (
  (SELECT COUNT(*) > 10 FROM UNNEST([1, 2, 3, 4, 5, 6]))
) AS 'Table must contain more than 10 rows.';

The following examples assert that the data source contains a particular value.

-- This query succeeds and no error is produced.
ASSERT
  EXISTS(
    (SELECT X FROM UNNEST([7877, 7879, 7883, 7901, 7907]) AS X WHERE X = 7907))
AS 'Column X must contain the value 7907.';
-- Error: Column X must contain the value 7919.
ASSERT
  EXISTS(
    (SELECT X FROM UNNEST([7877, 7879, 7883, 7901, 7907]) AS X WHERE X = 7919))
AS 'Column X must contain the value 7919';