策略性行为
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?（） Do not pass a user variable in the WHERE clause because it limits the ability of the optimizer to use indexes。 Add an index on the objective column so that is can be used in both the WHERE and GROUP BY operations。 Drop the run_2 index because it has caused a conflict in the choice of key for this query。 Execute the run_2 index because it has caused a conflict in the choice of key for this query。 Add a composite index on (run,objective,stage) to allow the query to fully utilize an index。
明代李时珍所著（）是世界闻名的药物学巨著，共收载药物（）种，现已译成（）种文本。
Which two statements accurately describe a role?（） A role can be given to a maximum of 1000 users.。 A user can have access to a maximum of 10 roles.。 A role can have a maximum of 100 privileges contained in it.。 Privileges are given to a role by using the CREATE ROLE statement.。 A role is a named group of related privileges that can be granted to the user.。 A user can have access to several roles, and several users can be assigned the same role.。
发电机失磁后，机组转速（）。 升高。 降低。 不变。
检查冷却水的液面高度，冷却水位应在离水箱盖深处（）的高度，如液面高度不足时应添加。
