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?（）

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

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热门试题

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

A.It prompts you to set the root user account password
B.It checks whether file permissions are appropriate within datadir
C.It asks to remove the test database, which is generated at installation time
D.It can delete any anonymous accounts
E.It verifies that all users are configuration with the longer password hash

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?（）

A.Syntax when writing queries involving JOINS
B.Memory usage when working with the data
C.Character set mapping index hash size
D.Disk usage when storing data

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A.Creating, dropping, and modifying tables and indexes
B.Initiating a binary backup of the database by using the START BACKUP command
C.Displaying replication status information
D.Shutting down the server by using the SHUTDOWN command
E.Creating and dropping databases
F.Creating and administering users

多项选择题Consider the events_% tables in performance Schema. Which two methods will clear or reset the collected events in the tables?（）

A.Using DELETE statements, for example, DELETE FROM performance_schema.events_watis_current
B.Using the statement RESET PERFORMANCE CACHE
C.Using the statement FLUSH PERFORMANCE CACHE
D.Using TRUNCATE statements, for example, TRUNATE TABLE performance_schema.events_waits_current
E.Disabling and re-enabling all instruments
F.Restarting Mysql