Answer 1

SELECT statement selects/chooses which fields from a certain table are to included in query results, on using asterisk (*) all fields from the table will be included. Better explanation here (reference):

https://www.w3schools.com/sql/sql_select.asp

SHOW COLUMNS displays information about the columns in a given table. More about it read at the following link:

https://mariadb.com/kb/en/library/show-columns/

Hth, cmiiw