DROP FUNCTION IF EXISTS format_time;   

DELIMITER $$   

CREATE FUNCTION format_time(picoseconds BIGINT)   
RETURNS VARCHAR(16) CHARSET UTF8 DETERMINISTIC 
BEGIN  
  IF picoseconds IS NULL THEN RETURN NULL;   
  ELSEIF picoseconds >= 60000000000000 THEN RETURN SEC_TO_TIME(picoseconds/1000000000000);   
  ELSEIF picoseconds >= 1000000000000 THEN RETURN CONCAT(ROUND(picoseconds / 1000000000000, 2), ' s');   
  ELSEIF picoseconds >= 1000000000 THEN RETURN CONCAT(ROUND(picoseconds / 1000000000, 2), ' ms');   
  ELSEIF picoseconds >= 1000000 THEN RETURN CONCAT(ROUND(picoseconds / 1000000, 2), ' µs');   
  ELSEIF picoseconds >= 1000 THEN RETURN CONCAT(ROUND(picoseconds / 1000, 2), ' ns');   
  ELSE RETURN CONCAT(picoseconds, ' ps');   
  END IF; 
END 

$$   

DELIMITER ; 

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mysql> select format_time(123456789);
ERROR 1305 (42000): FUNCTION test.format_time does not exist

mysql>
mysql> DELIMITER $$
mysql>
mysql> CREATE FUNCTION format_time(picoseconds BIGINT)
    -> RETURNS VARCHAR(16) CHARSET UTF8 DETERMINISTIC
    -> BEGIN
    ->   IF picoseconds IS NULL THEN RETURN NULL;
    ->   ELSEIF picoseconds >= 60000000000000 THEN RETURN SEC_TO_TIME(picoseconds/1000000000000);
    ->   ELSEIF picoseconds >= 1000000000000 THEN RETURN CONCAT(ROUND(picoseconds / 1000000000000, 2), ' s');
    ->   ELSEIF picoseconds >= 1000000000 THEN RETURN CONCAT(ROUND(picoseconds / 1000000000, 2), ' ms');
    ->   ELSEIF picoseconds >= 1000000 THEN RETURN CONCAT(ROUND(picoseconds / 1000000, 2), ' чs');
    ->   ELSEIF picoseconds >= 1000 THEN RETURN CONCAT(ROUND(picoseconds / 1000, 2), ' ns');
    ->   ELSE RETURN CONCAT(picoseconds, ' ps');
    ->   END IF;
    -> END
    ->
    -> $$
Query OK, 0 rows affected (0.11 sec)

mysql>
mysql> DELIMITER ;
mysql> select format_time(123456789);
+------------------------+
| format_time(123456789) |
+------------------------+
| 123.46 чs              |
+------------------------+
1 row in set (0.02 sec)

mysql> DROP FUNCTION IF EXISTS format_time;
Query OK, 0 rows affected (0.06 sec)

mysql>