1) Which of the following is a DDL (Data Definition Language) statement in SQL?

2) What is the purpose of the WHERE clause in a SQL SELECT statement?

3) What is the correct syntax for creating a table named "customers" with columns "customer_id" (integer) and "name" (varchar2(50)) in Oracle SQL?

4) Which DML statement is used to insert a new row into a table?

5) How can you update the "name" column of a customer with ID 100 to "John Doe" in the "customers" table?

6) What is the function of the GROUP BY clause in a SQL SELECT statement?

7) Which clause is used to calculate aggregate functions like SUM, AVG, COUNT, MIN, and MAX in SQL?

8) What type of join is used to return all rows from both tables, even if there are no matches between the joined columns?

9) Which join is used to return rows that have matching values in both tables?

10) What is the purpose of the ORDER BY clause in a SQL SELECT statement?

11) What is a subquery?

12) Which type of subquery is used to return a single value?

13) What is a view in SQL?

14) Which statement is used to create a view in SQL?

15) What is the purpose of an index in SQL?

16) Which type of index is used to improve performance for queries that filter data based on multiple columns?

17) Which function is used to convert a string to uppercase in Oracle SQL?

18) Which function is used to extract a substring from a string in Oracle SQL?

19) What is a constraint in SQL?

20) Which constraint is used to ensure that a column cannot contain null values?