单项选择题 Consider the query: Mysql＞ SET @run = 15; Mysql＞ EXPLAIN SELECT objective, stage, COUNT (stage) FROM iteminformation WHERE run=@run AND objective=’7.1’ GROUP BY objective,stage ORDER BY stage; The iteminformation table has the following indexes; Mysql＞ SHOW INDEXES FROM iteminformation: This query is run several times in an application with different values in the WHERE clause in a growing data set. What is the primary improvement that can be made for this scenario?（）

多项选择题 What are three actions performed by the mysql_secure_installation tool?（）

多项选择题 In a design situation, there are multiple character sets that can properly encode your data. Which three should influence your choice of character set?（）