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?（）
A、 Do not pass a user variable in the WHERE clause because it limits the ability of the optimizer to use indexes
B、 Add an index on the objective column so that is can be used in both the WHERE and GROUP BY operations
C、 Drop the run_2 index because it has caused a conflict in the choice of key for this query
D、 Execute the run_2 index because it has caused a conflict in the choice of key for this query
E、 Add a composite index on (run,objective,stage) to allow the query to fully utilize an index
相关问题推荐
在SQL*PLUS中显示EMP表结构的命令是（）
A、LIST EMP
B、DESC EMP
C、SHOW DESC EMP
D、STRUCTURE EMP
E、SHOW STRUCTURE EMP
What is the role of route preference?（）
A、It is used as a tie breaker when the same prefix is available through multiple sources
B、It is used to determine which routes to accept into the routing table
C、It is used to select the best route between multiple equal-cost paths
D、It is used to select which routing table to use for forwarding
在信息系统联网测试期间不得采用真实业务数据。如因联网测试发生安全事件，将追究（）相关责任。
A、信息通信系统业务主管部门
B、信息通信系统运维单位
C、信息通信系统研发单位
D、信息通信系统测评单位
违反《中华人民共和国网络安全法》规定，给他人造成损害的，依法承担（）。
A、刑事责任
B、行政责任
C、民事责任
若在程序中变量均已定义成int类型，且已赋大于1的值，则下列选项中能正确表示代数式1/abc的表达式是（ ）。
A、1.0/a/b/c
B、1/(a*b*c)
C、1.0/a*b*c
D、1/a/b/(double)c
