Database Transactions can occur concurrently by several users. This can cause issues with data consistency. To help resolve this problem, RDBMS can implement Read Consistency. Q4. What is Read Consistency? Q5. What are two problems that could occur without data/read consistency? 1. 2. Q6. What is Data Locking and how/why is it used?
Q4. What is Read Consistency?
Q5. What are two problems that could occur without data/read consistency?
1.
2.
Q6. What is Data Locking and how/why is it used?
Q7. Please review the following SQL statements and answer the following questions.
- On which line does the first commit occur?
- Is this first commit implicit or explicit?
- Which SQL DML statement is rolled back when line 12 is run?
- Which SQL DML statement is committed on line 16?
- Is the commit in line 16 implicit or explicit?
- Assume 10 of the ‘SA_REP’ employees start with a salary of 1000.00. What is their salary when 17 is run?
- NOTE: For those of you who are familiar with programming, assume there is no infinite loop here.
1 select * from employees;
2 DROP TABLE Employee_Project_Assignment;
3 UPDATE employees
4 SET salary = salary + salary * 1.05
5 WHERE job_id = 'ST_CLERK';
6 SAVEPOINT clerk_increase;
7 UPDATE employees
8 SET salary = salary + salary * 1.1
9 WHERE job_id = 'SA_REP';
10 SAVEPOINT sa_rep_increase;
11 SELECT SUM(salary) FROM employees;
12 ROLLBACK TO SAVEPOINT clerk_increase;
13 UPDATE employees
14 SET salary = salary + salary * 1.075
15 WHERE job_id = 'SA_REP';
16 COMMIT;
17 select * from employees;
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