题目
题目
单项选择题

Question at position 20 ________ is a set of commands used to update and query a database.DDL DPL DCL DML

选项
A.DDL
B.DPL
C.DCL
D.DML
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标准答案
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思路分析
Start by identifying what the question is asking: a set of commands used to update and query a database. Option A: DDL stands for Data Definition Language, which is used to define or modify the ......Login to view full explanation

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Question at position 17 ________ is a set of commands used to update and query a database.DDL DML DPL DCL

Please create the following data frame: library(tidyverse)student <- tibble(  sid = c(66666,66666,66666,66666,66666,66666,22222,22222,22222,22222,22222,           11111,11111,11111,11111,11111,44444,44444,44444,44444,44444, 44444,           55555,55555,55555,55555,55555,55555, 33333,33333,33333,33333,33333,33333, 77777),   course = c("COMM101", "COMM102", "COMM103", "COMM201", "COMM204","COMM205", "COMM101",              "COMM102", "COMM103", "COMM201","COMM204", "COMM101", "COMM102", "COMM103",              "COMM201", "COMM205", "COMM101", "COMM102", "COMM103", "COMM201","COMM204",              "COMM205", "COMM101", "COMM102", "COMM103","COMM201", "COMM204", "COMM205",             "COMM101", "COMM102", "COMM103", "COMM201", "COMM204","COMM205", "COMM205"),   year = c(2016, 2016, 2016, 2017, 2017, 2017, 2016, 2016, 2017, 2017,2017,2016, 2016,            2016, 2017, 2017, 2016, 2016, 2016, 2016, 2017, 2017,2016, 2016, 2016, 2016,            2017, 2017,2016, 2016, 2016, 2017, 2017, 2017, 2017),  grade = c(85, 88, 72, 67, 80, 90, 77, 77, 77, 77, 77, 78, 82, 82, 80, 90, 80, 80, 80,             85, 85, 85, 79, 80, 81, 82, 83, 84, 90, 88, 95, 80, 80, 80, 99))   You wanted to find out how many unique students have taken courses in 2016.  student %>%   filter(year == 2016) %>%   XXXX(sid) %>% summarise(XXXX(sid)) The result of your code should look something like this: # A tibble: 1 × 1             XXXXXXXXXX                                <int> 1                    6 Please complete the code below. student %>%   filter(year == 2016) %>%   [Fill in the blank] (sid) %>% summarise([Fill in the blank] (sid))  

Question at position 51 A database is maintained and queried using the data mapping language (DML).TrueFalse

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