单项选择题

What is true about joining tables through an equijoin?（）

A. You can join a maximum of two tables through an equijoin.
B. You can join a maximum of two columns through an equijoin.
C. You specify an equijoin condition in the SELECT or FROM clauses of a SELECT statement.
D. To join two tables through an equijoin, the columns in the join condition must be primary key and foreign key columns.
E. You can join n tables (all having single column primary keys) in a SQL statement by specifying a minimum of n-1 join conditions.

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多项选择题Which four are types of functions available in SQL? （）

A. string
B. character
C. integer
D. calendar
E. numeric
F. translation
G. date
H. conversion

单项选择题You need to calculate the total of all salaries in the accounting department. Which group function should you use?（）

A. MAX
B. MIN
C. SUM
D. COUNT
E. TOTAL
F. LARGEST

单项选择题You define a multiple-row subquery in the WHERE clause of an SQL query with a comparison operator = .What happens when the main query is executed?（）

A. The main query executes with the first value returned by the subquery.
B. The main query executes with the last value returned by the subquery.
C. The main query executes with all the values returned by the subquery.
D. The main query fails because the multiple-row subquery cannot be used with the comparison operator.
E. You cannot define a multiple-row subquery in the WHERE clause of a SQL query.

单项选择题A SELECT statement can be used to perform these three functions: 1. Choose rows from a table. 2. Choose columns from a table 3. Bring together data that is stored in different tables by creating a link between them. Which set of keywords describes these capabilities?（）

A. difference, projection, join
B. selection, projection, join
C. selection, intersection, join
D. intersection, projection, join
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多项选择题Which three statements correctly describe the functions and use of constraints? （）

A. Constraints provide data independence.
B. Constraints make complex queries easy.
C. Constraints enforce rules at the view level.
D. Constraints enforce rules at the table level.
E. Constraints prevent the deletion of a table if there are dependencies.
F. Constraints prevent the deletion of an index if there are dependencies.