Lab # 6. Data Manipulation Language (DML)

Transcription

1 Islamic University of Gaza Faculty of Engineering Department of Computer Engineering ECOM 4113: Lab # 6 Data Manipulation Language (DML) Eng. Haneen El-Masry December, 2014

2 2 Objective To be more familiar with SQL Language especially with Data Manipulation Language (DML). SUBQUERIES Q1: Retrieve all employees who has a salary greater than the average salaries in department 80. To solve this query, we need to know the average salaries in department 80. First Query: Then, we can use this value in a new query to find the employees who has a salary greater than it. Second Query:

3 3 A better solution is to embed the first query in the second query in two parentheses. This solution is called SUBQUERY solution, the first query is called INNER QUERY and the second query is called OUTER QUERY. Types of SUBQUERIES Single Row SUBQUERIES: Queries that return only one row from the inner SELECT statement. Multiple Row SUBQUERIES: Queries that return more than one row from the inner SELECT statement. A single row SUBQUERY uses a single row operator (>, <, =, <>, etc...). However, multiple-row SUBQUERY uses multiple-row operator (IN, ALL, ANY), instead of a single-row operator.

4 4 The multiple-row comparison operators are: Operator Meaning IN (set) Equal to any member in the list. ANY (set) Must be preceded by =, <>, >, <, <=, >=. Compares a value to each value in a list or returned by a query. Evaluates to FALSE if the query returns no rows. ALL (set) Must be preceded by =, <>, >, <, <=, >=. Compares a value to every value in a list or returned by a query. Evaluates to TRUE if the query returns no rows. Q2: Retrieve all employees who are working in departments 100 AND their salary is greater than ALL employees in department 60.

5 5 Q3: Retrieve all employees are not IT programmers and whose salary is less than that of any IT programmer. Q4: Retrieve all employees whose salary is less than the salary of all employees with a job ID of IT_PROG and whose job is not IT_PROG.

6 6 Q5: Retrieve the employee number and last name of all employees who work in a department with any employee whose last name contains the letter u. Q6: Retrieve the last name, department number, and job ID of all employees whose department location ID is 1700.

7 7 Set Operators Set Operators are used to combine the results of two or more component queries into one result. Queries containing set operators are called compound queries. In oracle, there are 4 Set Operators: UNION: return all rows from multiple tables and eliminate any duplicate rows. UNION ALL: return all rows from multiple tables including all duplicate rows. INTERSECT: return all rows from multiple tables and eliminate any duplicate rows. MINUS: return all rows from multiple tables and eliminate any duplicate rows. Notes: Column count of all component queries must be the same. Data types of retrieved columns should match or at least should be implicitly convertible by database. Q7: Retrieve department IDs for departments that do not contain the job ID ST_CLERK.

8 8 Q8: Retrieve name and id for all countries that have no departments located in them. DELETE DELETE statement is the opposite of INSERT statement. It is used to delete rows from a table according to a specified condition. DELETE Statement Syntax DELETE FROM table-name [WHERE condition]; If you want to empty a table, you just have to issue this command: DELETE FROM table-name. You should be aware when using this form.

9 9 UPDATE UPDATE statement is used to modify existing rows values in a table. UPDATE Statement Syntax UPDATE table name SET column1 = newvalue1, column2 = new_value2 -- etc WHERE condition;

10 10 Exercises 1. Write a query (without using set operators) to retrieve name and id for all countries that have no departments located in them. 2. Write a query to retrieve all employees whose salary is more than the salary of any employee from department Write a query to retrieve first name, last name, and department name, for employees whose salary is more than all their collagenous salaries in the same department. 4. Write SQL statement to modify all employees JOB_IDs to C_ENG, if there salary is between and Write SQL statement to delete all employees who are not working in any departments. 6. Write SQL statement to delete all employees who are working in department 80, but their total salary is less than Best Wishes