多选题Which four are attributes of single row functions? （）Acannot be nestedBmanipulate data itemsCact on each row returnedDreturn one result per rowEaccept only one argument and return only one valueFaccept arguments which can be a column or an expression

第1题：

which one of the following accurately describes field names?（）

• A、they must be unique in a database  
• B、they can only be used once in a view  
• C、they can only used once on each form  
• D、they can be used mulriple times on a form 

第2题：

Which two statements about subqueries are true? （）

• A、A subquery should retrieve only one row.
• B、A subquery can retrieve zero or more rows.
• C、A subquery can be used only in SQL query statements.
• D、Subqueries CANNOT be nested by more than two levels.
• E、A subquery CANNOT be used in an SQL query statement that uses group functions.
• F、When a subquery is used with an inequality comparison operator in the outer SQL statement, the column list in the SELECT clause of the subquery should contain only one column.

第3题：

第4题：

Which two statements about subqueries are true?（）

• A、A single row subquery can retrieve data from only one table.
• B、A SQL query statement cannot display data from table B that is referred to in its subquery, unless table B is included in the main query's FROM clause.
• C、A SQL query statement can display data from table B that is referred to in its subquery, without including table B in its own FROM clause.
• D、A single row subquery can retrieve data from more than one table.
• E、A single row subquery cannot be used in a condition where the LIKE operator is used for comparison.
• F、A multiple-row subquery cannot be used in a condition where the LIKE operator is used for comparison.

第5题：

Which three statements about subqueries are true?（）

• A、A single row subquery can retrieve only one column and one row.
• B、A single row subquery can retrieve only one row but many columns.
• C、A multiple row subquery can retrieve multiple rows and multiple columns.
• D、A multiple row subquery can be compared by using the ">" operator.
• E、A single row subquery can use the IN operator.
• F、A multiple row subquery can use the "=" operator.

第6题：

Which two statements are true about the primary key constraint in a table？ （）

• A、It is not possible to disable the primary key constraint.
• B、It is possible to have more than one primary key constraint in a single table.
• C、The primary key constraint can be referred by only one foreign key constraint.
• D、The primary key constraint can be imposed by combining more than one column.
• E、The non-deferrable primary key constraint creates an unique index on the primary key column if it is not already indexed.

第7题：

Which three statements about subqueries are true? （）

• A、A main query can have more than one subquery.
• B、A subquery can have more than one main query.
• C、The subquery and main query must retrieve data from the same table.
• D、The subquery and main query can retrieve data from different tables.
• E、Only one column or expression can be compared between the subquery and main query.
• F、Multiple columns or expression can be compared between the subquery and main query.

第8题：

Which three statements are true regarding subqueries?（）

• A、Subqueries can contain GROUP BY and ORDER BY clauses 
• B、Main query and subquery can get data from different tables 
• C、Main query and subquery must get data from the same tables 
• D、Subqueries can contain ORDER BY but not the GROUP BY clause 
• E、Only one column or expression can be compared between the main query and subquery
• F、 Multiple columns or expressions can be compared between the main query and subquery

第9题：

Which two are true about aggregate functions? （）

• A、You can use aggregate functions in any clause of a SELECT statement.
• B、You can use aggregate functions only in the column list of the select clause and in the WHERE clause of a SELECT statement.
• C、You can mix single row columns with aggregate functions in the column list of a SELECT statement by grouping on the single row columns.
• D、You can pass column names, expressions, constants, or functions as parameter to an aggregate function.
• E、You can use aggregate functions on a table, only by grouping the whole table as one single group.
• F、You cannot group the rows of a table by more than one column while using aggregate functions.

第10题：

Which three statements are true regarding single-row functions？（）

• A、 They can accept only one argument.
• B、 They can be nested up to only two levels.
• C、 They can return multiple values of more than one data type.
• D、 They can be used in SELECT， WHERE， and ORDER BY clauses.  
• E、 They can modify the data type of the argument that is referenced.
• F、 They can accept a column name， expression， variable name， or a user-supplied constant as arguments.