explain 
select sign(0) FROM src LIMIT 1;
select sign(0) FROM src LIMIT 1;

select sign(-45) FROM src LIMIT 1;

select sign(46)  FROM src LIMIT 1;

DESCRIBE FUNCTION sign;
DESCRIBE FUNCTION EXTENDED sign;
explain 
select sign(0) FROM src LIMIT 1;
select sign(0) FROM src LIMIT 1;

select sign(-45) FROM src LIMIT 1;

select sign(46)  FROM src LIMIT 1;

DESCRIBE FUNCTION sign;
DESCRIBE FUNCTION EXTENDED sign;