GIFT Department of Computing Science Data Selection and Filtering using the SELECT Statement

Transcription

1 GIFT Department of Computing Science [Spring 2013] CS-217: Database Systems Lab-2 Manual Data Selection and Filtering using the SELECT Statement V1.0 4/12/2016

2 Introduction to Lab-2 This lab reinforces the concepts introduced in Lab-1 and extends the usage of the SELECT statement for data selection and data filtering. Is also introduces the usage of common arithmetic function using the SELECT statement. Finally, students are introduced to the usage of WHERE clause for the selection of data using the SELECT statement. The main topics of this lab include: 1. Introduction to Structured Query Language (SQL) 2. Capabilities of SQL SELECT Statements 3. Basic SELECT Statement 4. Selecting ALL Columns 5. Selecting Specific Columns 6. Writing SELECT Statements 7. Column Heading Defaults 8. Arithmetic Expressions 9. Using Arithmetic Operators 10. Operator Precedence & Parenthesis 11. Column Aliases 12. Null Values 13. Concatenation Operator ( ) 14. Literal Character Strings 15. Eliminating Duplicate Rows 16. Limiting Rows Using Selection: the WHERE Clause 17. Character Strings and Dates 18. Comparison Conditions (=, >, <, >=, <=, <>, BETWEEN, IN, LIKE, IS NULL) 19. String Wildcards (%, _) 20. Using the NULL Conditions 21. Logical Conditions (AND, OR, NOT) 22. ORDER BY Clause 23. Practice SQL Statements 24. SOLUTIONS: Practice SQL Statements Objectives of this Lab At the end of this lab, students should be able to: Understand the usage of SELECT statement for displaying selected rows Understand the usage of various conditional and logical operators in the SELECT statement Understand the usage of simple string matching using LIKE and string wildcards Spring 2016 CS-217: Database Systems (Lab) Page 1

3 Understand how to use the SQL SELECT statement for creating queries having multiple selection criteria Understand how to display data in sorted order using the SELECT statement 1. Introduction to Structured Query Language (SQL) SQL (Structured Query Language) is the standard relational query language with statements to create, remove, retrieve and maintain data in a relational database. SQL contains three main types of commands, Data Definition language (DDL), Data Manipulation language (DML), and Data Control language (DCL) statements. 2. Capabilities of SQL SELECT Statements The SELECT statement is the most frequently used statement in SQL; it is used to retrieve data from one or more tables. The names of the tables used in the statement must be listed in the statement. Using a SELECT statement, you can do the following: Projection: Choose the columns in a table that are returned by a query. Choose as few or as many of the columns as needed Selection: Choose the rows in a table that are returned by a query. Various criteria can be used to restrict the rows that are retrieved. Spring 2016 CS-217: Database Systems (Lab) Page 2

4 Joining: Bring together data that is stored in different tables by specifying the link between them. SQL joins are covered in more detail in a later lab. 3. Basic SELECT Statement SELECT * {[DISTINCT] column expression [alias],...} FROM table; In its simplest form, a SELECT statement must include the following: A SELECT clause, which specifies the columns to be displayed A FROM clause, which identifies the table containing the columns that are listed in the SELECT clause In the syntax: SELECT is a list of one or more columns * selects all columns DISTINCT suppresses duplicates column expression selects the named column or the expression alias gives selected columns different headings FROM table specifies the table containing the columns Note: Throughout these labs, the words keyword, clause, and statement are used as follows: A keyword refers to an individual SQL element. For example, SELECT and FROM are keywords. A clause is a part of a SQL statement. For example, SELECT employee_id, last_name,... is a clause. A statement is a combination of two or more clauses. For example, SELECT * loyees is a SQL statement. 4. Selecting ALL Columns SELECT * FROM dept; You can display all columns of data in a table by following the SELECT keyword with an asterisk (*).You can also display all columns in the table by listing all the columns after the SELECT keyword. 5. Selecting Specific Columns You can use the SELECT statement to display specific columns of the table by specifying the column names, separated by commas. This example below displays all the employee numbers, employee names, and salaries from the EMP table. SELECT empno, ename, sal ; Spring 2016 CS-217: Database Systems (Lab) Page 3

5 Note: In the SELECT clause, specify the columns that you want, in the order in which you want them to appear in the output. 6. Writing SELECT Statements Using the following simple rules and guidelines, you can construct valid statements that are both easy to read and easy to edit: SQL statements are not case-sensitive (unless indicated). SQL statements can be entered on one or many lines. Keywords cannot be split across lines or abbreviated. Clauses are usually placed on separate lines for readability and ease of editing. Indents should be used to make code more readable. Keywords typically are entered in uppercase; all other words, such as table names and columns, are entered in lowercase. 7. Column Heading Defaults In SQL+, column headings are displayed as uppercase. The column names are used for the default headings. For example, SELECT empno, ename, job ; Note: Character and Date column headings are left-aligned. Number column headings are rightaligned. 8. Arithmetic Expressions You may need to modify the way in which data is displayed, or you may want to perform calculations or look at what-if scenarios. These are all possible using arithmetic expressions. An arithmetic expression can contain column names, constant numeric values, and the arithmetic operators. Arithmetic Operators The following arithmetic operators are available in SQL. You can use arithmetic operators in any clause of a SQL statement (except the FROM clause). Operator Description + Add - Subtract * Multiply / Divide Spring 2016 CS-217: Database Systems (Lab) Page 4

6 Note: With DATE and TIMESTAMP data types, you can use the addition and subtraction operators only. 9. Using Arithmetic Operators You can create expressions using date and numeric data using mathematical operators (+, -, *, /). SELECT ename, sal, sal ; This example uses the addition operator to calculate a salary increase of $300 for all employees. This example also displays a SAL+300 column in the output. Note that the resultant calculated column SAL+300 is not a new column in the EMP table; it is for display only. By default, the name of a new column comes from the calculation that generated it in this case, sal+300. Note: The Oracle server ignores blank spaces before and after the arithmetic operator. 10. Operator Precedence & Parenthesis In mathematical expressions, multiplication and division takes priority over addition and subtraction. If operators within an expression are of same priority, then evaluation is done from left to right. You can use parenthesis to force the expression within parenthesis to be evaluated first. SELECT ename, sal, 12*sal+100 ; You can override the rules of precedence by using parentheses to specify the desired order in which operators are to be executed. SELECT ename, sal, 12*(sal+100) ; Rules of Precedence: Multiplication and division occur before addition and subtraction. Operators of the same priority are evaluated from left to right. Parentheses are used to override the default precedence or to clarify the statement. Spring 2016 CS-217: Database Systems (Lab) Page 5

7 11. Column Aliases You can override a column heading display with a column alias. It renames a column heading into something that is specified by the user. It is useful for reporting and calculations. The alias immediately follows the column name and is enclosed in double quotation marks. There could also be an optional AS keyword between the column name and the alias name. For example, 1. SELECT ename AS Employee Name ; 2. SELECT ename Employee Name, mgr Manager ; 3. SELECT ename Employee Name, sal*12 Annual Salary ; 12. Null Values A null is a value that is unavailable, unassigned, unknown, or inapplicable. If a column is missing a value, then that column is said to be null, or contains null. A null is not the same as a zero or a space. A zero is a number, and a space is a character. SELECT ename, sal, comm ; Applying a mathematical operator on a null value does not change its value. SELECT ename, sal, comm AS New Commission ; Note: Columns of any data type can contain nulls. However, some constraints (NOT NULL and PRIMARY KEY) prevent nulls from being used in the column. In the COMM column in the EMP table, notice that only a sales manager or sales representative can earn a commission. Other employees are not entitled to earn commissions. A null represents that fact. 13. Concatenation Operator ( ) You can link columns to other columns, arithmetic expressions, or constant values to create a character expression by using the concatenation operator ( ). Columns on either side of the operator are combined to make a single output column. 1. SELECT ename job ; 2. SELECT ename job AS New Data ; Spring 2016 CS-217: Database Systems (Lab) Page 6

8 Null Values with the Concatenation Operator If you concatenate a null value with a character string, the result is a character string. ENAME NULL results in ENAME. 14. Literal Character Strings A literal value is a character, a number, or a date that is included in the SELECT list and that is not a column name or a column alias. It is printed for each row returned. Date and character literals must be enclosed in single quotation marks ( ). Number literals need not. 1. SELECT Employee ename works as a job Employee Details ; 2. SELECT Employee ename was hired on hiredate is working as job and is getting sal AS New Data ; 15. Eliminating Duplicate Rows The default display of queries is all rows, including duplicate rows. SELECT deptno ; To eliminate duplicate rows in the result, include the DISTINCT keyword in the SELECT clause immediately after the SELECT keyword. SELECT DISTINCT deptno ; You can specify multiple columns after the DISTINCT qualifier. The DISTINCT qualifier affects all the selected columns, and the result is every distinct combination of the columns. SELECT DISTINCT deptno, job ; 16. Limiting Rows Using Selection: the WHERE Clause You can restrict the rows returned from the query by using the WHERE clause. A WHERE clause contains a condition that must be met, and it directly follows the FROM clause. If the condition is true, the row meeting the condition is returned. SELECT <criteria> FROM <table> [WHERE condition(s)]; Spring 2016 CS-217: Database Systems (Lab) Page 7

9 The WHERE clause can compare values in columns, literal values, arithmetic expressions, or functions. SELECT empno, ename, job, deptno WHERE deptno = 30; 17. Character Strings and Dates Character strings and dates in the WHERE clause must be enclosed in single quotation marks ( ). Number constants should not be enclosed in single quotation marks. All character searches are case sensitive. 1. SELECT empno, job, deptno WHERE ename = WARD ; 2. SELECT * WHERE hiredate = ; 3. SELECT * WHERE ename = king ; 4. SELECT empno, ename, job, deptno WHERE deptno = 30; Note: Oracle databases store dates in an internal numeric format, representing the century, year, month, day, hours, minutes, and seconds. The default date display is DD-MON-RR. 18. Comparison Conditions Comparison conditions are used in conditions that compare one expression to another value or expression. Operator Meaning = Equal to > Greater than >= Greater than or equal to < Less than Spring 2016 CS-217: Database Systems (Lab) Page 8

10 <= Less than or equal to <>,!=, ^= Not equal to BETWEEN AND IN (set) LIKE IS NULL Between two values inclusive Match any of a list a values Match a character pattern Is a null value Note: 1. SELECT empno, ename, job, sal WHERE sal <= 3000; 2. SELECT * WHERE hiredate > ; 3. SELECT ename, sal WHERE sal BETWEEN 2500 AND 3500; 4. SELECT empno, ename, sal, deptno WHERE mgr IN (7698, 7566, 7782); 5. SELECT empno, ename WHERE ename BETWEEN KING AND SMITH ; 6. SELECT empno, ename WHERE ename IN ( KING, SMITH ); An alias cannot be used in the WHERE clause. Values that are specified with the BETWEEN condition are inclusive. You must specify the lower limit first. You can also use the BETWEEN condition on character values. The IN condition can be used with any data type. Spring 2016 CS-217: Database Systems (Lab) Page 9

11 19. String Wildcards ( %, _ ) You may select rows that match a character pattern by using the LIKE condition. The character pattern-matching operation is referred to as wildcard search. Two symbols can be used to construct the search string: Symbol Description % Represents any sequence of zero or more characters _ Represents any single character 1. SELECT empno, ename, job, sal WHERE ename LIKE S% ; 2. SELECT empno, ename, job, sal WHERE ename LIKE _I% ; 3. SELECT empno, ename, job, sal WHERE ename LIKE %N ; The LIKE condition can be used as a shortcut for some BETWEEN comparisons. The following example displays the last names and hire dates of all employees who joined between January 1995 and December 1995: SELECT ename, hiredate WHERE hiredate LIKE '%95'; 20. Using the NULL Conditions The NULL conditions include the IS NULL condition and the IS NOT NULL condition. The IS NULL condition tests for nulls. We cannot use a = to test nulls. 1. SELECT empno, ename, job, sal WHERE mgr IS NULL; 2. SELECT empno, ename, job, sal WHERE comm IS NOT NULL; Spring 2016 CS-217: Database Systems (Lab) Page 10

12 3. SELECT empno, ename, sal, deptno WHERE comm IS NULL; 4. SELECT empno, ename, sal, deptno WHERE comm IS NOT NULL; 21. Logical Conditions (AND, OR, NOT) A logical condition combines the result of two component conditions to produce a single result based on them or inverts the result of a single condition. A row is returned only if the overall result of the condition is true. Operator AND OR NOT Meaning Returns TRUE if both component conditions are true Returns TRUE if either component condition is true Returns TRUE if the following condition is false 1. SELECT empno, ename, job, sal WHERE sal >= 2000 AND job LIKE %MAN% ; 2. SELECT empno, ename, job, sal WHERE sal >= 2000 OR job LIKE %MAN% ; 3. SELECT empno, ename, job, sal WHERE job NOT IN ( PRESIDENT, CLERK ); 22. ORDER BY Clause The order of rows returned in a query result is undefined. The ORDER BY clause can be used to sort the rows. If you use the ORDER BY clause, it must be the last clause of the SELECT statement. The value ASC will be used to sort data in ascending order (default order), and DESC will sort the data in descending order. 1. SELECT ename, job, sal ORDER BY hiredate; 2. SELECT ename, job, sal Spring 2016 CS-217: Database Systems (Lab) Page 11

13 ORDER BY empno DESC; You can also sort using the column alias in the ORDER BY clause. SELECT ename, sal, 12 * sal AS NewSal ORDER BY NewSal; You can also sort query result on more than one column. SELECT empno, ename, sal, deptno ORDER BY deptno, sal DESC; You can also sort by a column that is not included in the SELECT list. 23. Practice SELECT Statements Write SELECT statements for the following: 1. List the names and jobs for all employees. 2. List the employee ids, hire dates, and department numbers of all employees. 3. List the names, salaries and hire dates of all employees. 4. List the department number and names of all departments. 5. List the locations of all departments. 6. List the names and locations of all departments. 7. List all the grades and the low salary figures. 8. List all the low and high salary figures. 9. List all data from the department table. 10. List all data from the bonus table. 11. List all data from the salgrade table. 12. Create a query to display unique jobs from the employee table. 13. Display the name concatenated with job, separated by a comma and space, and name the column Employee and Title. 14. Create a query to display all the data from the employee table. Separate each column by a comma. Name the column The_Output. 15. Create a query to display the name and salary of employees earning more than Create a query to display the name and department number for employee number Display the employee name, job, and start date of employees hired between June 9, 1981 and July 13, Display the name and department number of all employees in departments 20 and 30 in alphabetical order by name. Spring 2016 CS-217: Database Systems (Lab) Page 12

14 19. Display the name and hiredate of every employee who was hired on July 13, Display the name and job title of all employees who do not have a manager. 21. Display the name, salary and commission of all employees who earn commission. Sort the data in descending order of salary and commissions. 22. Display the names of all employees where the third letter of the name is A. 23. Display the names of all employees who have an A and E in their names. 24. Display the name, job, and salary of all employees whose job is salesman or clerk and whose salary is not equal to 1000, 1500, or Due to budget issues, the HR department needs a report that displays the name and salary of employees who earn more than $2,000. Place your SQL statement in a text file named lab_02_01.sql. Run your query. 26. The HR departments needs to find high-salary and low-salary employees. Modify lab_02_01.sql to display the name and salary for any employee whose salary is not in the range of $1,500 to $3,000. Place your SQL statement in a text file named lab_02_03.sql. 27. Create a report to display the last name, job ID, and start date for the employees with the names of Allen and Blake. Order the query in ascending order by start date. 28. Display the last name and department number of all employees in departments 10 or 30 in ascending alphabetical order by name. 29. Modify lab_02_03.sql to display the last name and salary of employees who earn between $2,200 and $2,900 and are in department 20 or 30. Label the columns Employee and Monthly Salary, respectively. Resave lab_02_03.sql as lab_02_06.sql. Run the statement in lab_02_06.sql. 30. The HR department needs a report that displays the last name and hire date for all employees who were hired in Modify lab_02_06.sql to display the last name, salary, and commission for all employees whose commission amount is 20%. Resave lab_02_06.sql as lab_02_15.sql. Rerun the statement in lab_02_15.sql. Spring 2016 CS-217: Database Systems (Lab) Page 13

15 24. SOLUTIONS: Practice SELECT Statements 1. SELECT ename, job ; 2. SELECT empno, hiredate, deptno ; 3. SELECT ename, sal, hiredate ; 4. SELECT deptno, dname FROM dept; 5. SELECT loc FROM dept; 6. SELECT dname, loc FROM dept; 7. SELECT grade, losal FROM salgrade; 8. SELECT losal, hisal FROM salgrade; 9. SELECT * FROM dept; 10. SELECT * FROM bonus; 11. SELECT * FROM salgrade; 12. SELECT DISTINCT(job) ; 13. SELECT ename, job AS Employee and Title ; 14. SELECT empno, ename, job, mgr, hiredate, sal, comm, deptno AS The_Output ; 15. SELECT ename, sal WHERE sal > 1000; 16. SELECT ename, deptno WHERE empno = 7566; 17. SELECT ename, job, hiredate WHERE hiredate BETWEEN 9-JUN-81 AND 13-JUL-87 ; 18. SELECT ename, deptno WHERE deptno IN(20, 30) ORDER BY ename; 19. SELECT ename, hiredate WHERE hiredate = 13-JUL-87 ; 20. SELECT ename, job WHERE mgr IS NULL; 21. SELECT ename, sal, comm WHERE comm IS NOT NULL ORDER BY sal DESC, comm DESC; 22. SELECT ename WHERE ename LIKE A% ; 23. SELECT ename WHERE ename LIKE %A%E% ; 24. SELECT ename, job, sal WHERE job IN( SALESMAN, CLERK ) AND sal NOT IN(1000, 1500, 2000); Spring 2016 CS-217: Database Systems (Lab) Page 14

16 25. SELECT ename, sal WHERE sal > 2000; Copy this query in a text file, named as lab_02_01.sql. Open the.sql file for query execution. 26. SELECT ename, sal WHERE sal NOT BETWEEN 1500 AND 3000; Place this query in a file named lab_02_03.sql. 27. SELECT ename, job, hiredate WHERE ename IN( ALLEN, BLAKE ) ORDER BY hiredate; 28. SELECT ename, deptno WHERE deptno IN(10, 30) ORDER BY ename; 29. SELECT ename AS Employee, sal AS Salary WHERE ( sal BETWEEN 2200 AND 2900 ) AND ( deptno IN(20, 30) ) ; Place this query in a file named lab_02_06.sql. Open the.sql file for query execution. 30. SELECT ename, hiredate WHERE hiredate LIKE %94 ; 31. SELECT ename, sal, comm WHERE comm = 0.2; Place this query in a file named lab_02_15.sql. Open the.sql file for query execution. Spring 2016 CS-217: Database Systems (Lab) Page 15