This SQL query:
select c1 from table where c1='';
It's all stated there in the documentation. I've quoted the important points here. But I would suggest to go through the full documentation
VARCHAR values are not padded when they are stored. Trailing spaces are retained when values are stored and retrieved, in conformance with standard SQL.
On the other hand, CHAR values are padded when they are stored but trailing spaces are ignored when retrieved.
All MySQL collations are of type PADSPACE. This means that all CHAR, VARCHAR, and TEXT values in MySQL are compared without regard to any trailing spaces. “Comparison” in this context does not include the LIKE pattern-matching operator, for which trailing spaces are significant.
Trailing spaces are ignored while comparing strings using comparison operator ('='). But trailing spaces are significant for
pattern matching operator)