ASSERT_TRUE Function

assert_true(expr)
assert_true(expr, message)

Description

The ASSERT_TRUE function validates whether a boolean expression is true. If the expression is true, it returns NULL; if the expression is false or NULL, it throws an exception. The optional message parameter allows a custom error message.

This function is commonly used for data quality checks, unit testing, and runtime assertion validation.

Parameters

• expr: A boolean expression, required. The condition to validate.
• message: A string value, optional. A custom error message displayed when the assertion fails. If not specified or NULL, the default error message "ASSERT_TRUE expr is not true!" is used.

Returns

• When expr is true: Returns NULL.
• When expr is false or NULL: Throws an exception with the error message.

Examples

1. Basic usage - assertion succeeds, returns NULL:

   SELECT assert_true(1 = 1);
   +---------------------+
   | assert_true(1 = 1)  |
   +---------------------+
   | NULL                |
   +---------------------+
   

2. Using a custom error message - assertion succeeds:

   SELECT assert_true(10 > 5, 'Ten is greater than five');
   +--------------------------------------------------+
   | assert_true(10 > 5, 'Ten is greater than five')  |
   +--------------------------------------------------+
   | NULL                                             |
   +--------------------------------------------------+
   

3. Assertion fails - throws default error message:

   SELECT assert_true(1 > 2);
   -- Error: ASSERT_TRUE expr is not true!
   

4. Assertion fails - throws custom error message:

   SELECT assert_true(1 > 2, 'One should be greater than two');
   -- Error: One should be greater than two
   

5. Input is NULL - treated as assertion failure:

   SELECT assert_true(NULL);
   -- Error: ASSERT_TRUE expr is not true!
   

Notes

• When expr is NULL, it is treated as an assertion failure and throws an exception (rather than returning NULL).
• When message is NULL, the default error message "ASSERT_TRUE expr is not true!" is used.
• This function is compatible with Spark's assert_true semantics.
• This function is not subject to constant folding optimization, ensuring that assertion checks are always executed at runtime.