Mysql->order by SQL Sort by multiple criteria

Sort by multiple criteria in MySQL: (separated by commas between each condition)

First, based on the length of the class_name string in ascending order, and then descending according to the start time:

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1. SELECT * from Signup_class s ORDER by ifnull (Length (Trim (s.class_name)), 0) Asc,s.date_start DESC

Comments:

Trim (s.class_name): Remove spaces in a string
Length (Trim (s.class_name): string length after whitespace removal
Ifnull (EXPR1,EXPR2): If not empty, take expr1, if it is empty, take EXPR2
ASC: Sort in ascending order;
Desc: Sort in descending order.

Mysql->order by SQL Sort by multiple criteria