为什么在选留种鱼时要留足一定数量的亲鱼？
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。
条形基础根据基础深度宜分段分层连续浇筑混凝土，一般不留（）。 斜槎。 施工缝。 沉降缝。 防震缝。
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.。
起重机钢丝绳用卡子连接时，根据钢丝绳直径不同，使用不同数量的卡子，但最小不得少于（）。
