Google Standard SQL for BigQuery 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.
An ASSERT statement is billed in the same way as the query "SELECT
expression", except that the result of an ASSERT statement is never cached.
Examples
The following example asserts that the data source contains over five rows. The statement succeeds.
ASSERT (
(SELECT COUNT(*) FROM UNNEST([1, 2, 3, 4, 5, 6])) > 5
) AS 'Table must contain more than 5 rows.';
The following example asserts that the source table contains a particular value.
ASSERT
EXISTS(
SELECT X
FROM UNNEST([7877, 7879, 7883, 7901, 7907]) AS X
WHERE X = 7919
)
AS 'Column X must contain the value 7919';
The above statement generates this error:
Assertion failed: Column X must contain the value 7919