@alex_b it is a very common observation to get confused between the syntaxes of the DATEDIFF & TIMESTAMPDIFF functions.
Following link will certainly help with the syntax of DATEDIFF &
this page will list all the others date related functions available in MariaDB's parent MySQL.\
Referencing the links above below is a summary -
TIMEDIFF(expr1,expr2)
expr1 - '2000:01:01 00:00:00'
expr2 - '2000:01:01 00:00:00.000001'
TIMEDIFF() returns expr1 − expr2 expressed as a time value. expr1 and
expr2 are time or date-and-time expressions, but both must be of the
same type.
DATEDIFF(expr1,expr2)
expr1 - '2007-12-31 23:59:59'
expr2 - '2007-12-30'
DATEDIFF() returns expr1 − expr2 expressed as a value in days from one
date to the other. expr1 and expr2 are date or date-and-time
expressions. Only the date parts of the values are used in the
calculation.
Below is the scenario I used it for -
- using CURDATE for current date as 'argument1'
- using existing varchar column as 'argument2'
- using SET command to update a column
SET output_date = DATEDIFF(CURDATE(),input_date),
...
above worked for me. Good luck!