IF FUNCTION is FALSE and the false_value parameter is a function, then an exception will be thrown

It is successful to execute certain functions individually.

SELECT SPLIT_INDEX('TEST:ABC', ':', 0); 

And it is also successful for these functions to be located in the true_value parameter of the IF function.

SELECT IF(2>1, SPLIT_INDEX('TEST:ABC', ':', 1), 'FALSE'); 

Only when these functions are located in the false_value parameter of the IF function, an exception will be thrown.

 func1.

SELECT IF(2>1, 'TRUE', SPLIT_INDEX('TEST:ABC', ':', 0)); 

func2. 

SELECT IF(2>1, 'TRUE', LOWER('TEST')); 

 
And it is also successful for CASE function

SELECT CASE WHEN 2=1 THEN 'TRUE' ELSE SPLIT_INDEX('TEST:ABC', ':', 0) END;