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?（）

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
E. difference, projection, product

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.

单项选择题Which is a valid CREATE TABLE statement?（）

A. CREATE TABLE EMP9$# AS (empid number(2));
B. CREATE TABLE EMP*123 AS (empid number(2));
C. CREATE TABLE PACKAGE AS (packid number(2));
D. CREATE TABLE 1EMP_TEST AS (empid number(2));

多项选择题Which two are character manipulation functions?（）

A. TRIM
B. REPLACE
C. TRUNC
D. TO_DATE
E. MOD
F. CASE

多项选择题Which three are true?（）

A. A MERGE statement is used to merge the data of one table with data from another.
B. A MERGE statement replaces the data of one table with that of another.
C. A MERGE statement can be used to insert new rows into a table.
D. A MERGE statement can be used to update existing rows in a table.