Restricting and Sorting Data

Objectives

After completing this lesson, you should be able to do the following:

Limit the rows retrieved by a querySort the rows retrieved by a query

Limiting Rows Using a Selection

"…retrieve allemployees

in department 10"

Employeeemployee_nbr name job ... dept_nbr

7839 King President 10 7698 Blake Manager 30 7782 Clark Manager 10 7566 Jones Manager 20 ...

Employeeemployee_nbr name job ... dept_nbr

7839 King President 107782 Clark Manager 10

7934 Miller Manager 10 ...

Limiting Rows Selected

Restrict the rows returned by using the WHERE clause.

The WHERE clause follows the FROM clause.

SELECT [DISTINCT] {*| column [alias], ...}FROM table[WHERE condition(s)];

Using the WHERE Clause

MySQL>SELECT name, job, dept_nbr 2 FROM employee 3 WHERE job=‘Clerk’;

name job dept_nbr--------- --------- ---------James Clerk 30Smith Clerk 20Adams Clerk 20Miller Clerk 10

Character Strings and Dates

Character strings and date values are enclosed in single quotation marks.Character values are case sensitive and date values are format sensitive.The default date format is YYYY-MM-DD.

MySQL>SELECT name, job, dept_nbr 2 FROM employee 3 WHERE name = ;‘James’

Comparison Operators

Operator Meaning= Equal to> Greater than

>= Greater than or equal to< Less than

<= Less than or equal to<> Not equal to!= Not equal to

Using the Comparison Operators

MySQL>SELECT name, salary, commission 2 FROM employee 3 WHERE salary <= commission;

name salary commission---------- --------- ----------Martin 1250 1400

Other Comparison Operators

Operator MeaningBETWEEN…AND…

Between two values (inclusive)

IN (list) Match any of a list of values

LIKE Match a character pattern

IS NULL Is a null value

Using the BETWEEN Operator

Use the BETWEEN operator to display rows based on a range of values.

name salary---------- ---------Martin 1250Turner 1500Ward 1250Adams 1100Miller 1300

MySQL>SELECT name, salary 2 FROM employee 3 WHERE salary BETWEEN 1000 AND 1500;

Lowerlimit

Higherlimit

Using the IN Operator

Use the IN operator to test for values in a list.

MySQL>SELECT employee_nbr, name, salary, manager 2 FROM employee 3 WHERE manager IN (7902, 7566, 7788);

employee_nbr name salary manager------------ ---------- -------- --------- 7902 FORD 3000 7566 7369 SMITH 800 7902 7788 SCOTT 3000 7566 7876 ADAMS 1100 7788

Using the LIKE Operator

MySQL>SELECT name 2 FROM employee 3 WHERE name LIKE 'S%';

Use the LIKE operator to perform wildcard searches of valid search string values.Search conditions can contain either literal characters or numbers.

% denotes zero or many characters._ denotes one character.Searches are case sensitive.

Using the LIKE Operator

You can combine pattern-matching characters.You can use the ESCAPE identifier to search for "%" or "_".

MySQL>SELECT name 2 FROM employee 3 WHERE name LIKE ‘_a%’;

name---------- MartinJames Ward

Using the IS NULL Operator

Test for null values with the IS NULL operator.

MySQL>SELECT name, manager 2 FROM employee 3 WHERE manager IS NULL;

name manager---------- ---------King

Logical Operators

Operator Meaning

ANDReturns TRUE if both component conditions are TRUE

ORReturns TRUE if either component conditions is TRUE

NOTReturns TRUE if the following condition is FALSE

Using the AND Operator

MySQL>SELECT employee_nbr, name, job, salary 2 FROM employee 3 WHERE salary >= 1100 4 AND job = 'Clerk';

employee_nbr name job salary------------ ------- --------- --------- 7876 Adams Clerk 1100 7934 Miller Clerk 1300

AND requires both conditions to be TRUE.

Using the OR Operator

MySQL>SELECT employee_nbr, name, job, salary 2 FROM employee 3 WHERE salary >= 1100 4 OR job = ‘Clerk’;

employee_nbr name job salary------------ ------- --------- --------- 7839 King President 5000 7698 Blake Manager 2850 7782 Clark Manager 2450 7566 Jones Manager 2975 7654 Martin Salesman 1250 ... 7900 James Clerk 950 ...14 rows selected.

OR requires either conditions to be TRUE.

Using the NOT Operator

MySQL>SELECT name, job 2 FROM employee 3 WHERE job NOT IN ('Clerk','Manager',’Analyst');

name job---------- ---------King PresidentMartin SalesmanAllen SalesmanTurner SalesmanWard Salesman

Rules of Precedence

Override rules of precedence by using parentheses.

Order Evaluated Operator

1 All comparison operators

2 NOT

3 AND

4 OR

Rules of Precedence

name job Salary---------- --------- ---------King President 5000Martin Salesman 1250Allen Salesman 1600Turner Salesman 1500Ward Salesman 1250

MySQL>SELECT name, job, salary 2 FROM employee 3 WHERE job = ‘Salesman’ 4 OR job = ‘President’ 5 AND salary > 1500;

Rules of Precedence

name job salary---------- --------- ---------King President 5000Allen Salesman 1600

MySQL>SELECT name, job, salary 2 FROM employee 3 WHERE (job = ‘Salesman’ 4 OR job = ‘President’) 5 AND salary > 1500;

Use parentheses to force priority.

ORDER BY ClauseSort rows with the ORDER BY clause

ASC: ascending order, defaultDESC: descending order

The ORDER BY clause comes last in the SELECT statement.

MySQL>SELECT name, job, dept_nbr, hire_date 2 FROM employee 3 ORDER BY hire_date;

name job dept_nbr hire_date---------- --------- --------- ---------Smith Clerk 20 1980-12-17Allen Salesman 30 1981-02-20...14 rows selected.

Sorting in Descending OrderMySQL>SELECT name, job, dept_nbr, hire_date 2 FROM employee 3 ORDER BY hire_date DESC;

name job dept_nbr hire_date---------- --------- --------- ---------Adams Clerk 20 1983-01-12Scott Analyst 20 1982-12-09Miller Clerk 10 1982-01-23James Clerk 30 1981-12-03Ford Analyst 20 1981-12-03King President 10 1981-11-17Martin Salesman 30 1981-09-28...14 rows selected.

Sorting by Column Alias

MySQL>SELECT employee_nbr, name, salary*12 annual_salary 2 FROM employee 3 ORDER BY annual_salary;

employee_nbr name annual_salary------------ --------- ------------- 7369 SMITH 9600 7900 JAMES 11400 7876 ADAMS 13200 7654 MARTIN 15000 7521 WARD 15000 7934 Miller 15600 7844 TURNER 18000...14 rows selected.

Sorting by Multiple ColumnsThe order of ORDER BY list is the order of sort.

MySQL>SELECT name, dept_nbr, salary 2 FROM employee 3 ORDER BY dept_nbr, salary DESC;

name dept_nbr Salary---------- --------- ---------King 10 5000Clark 10 2450Miller 10 1300Ford 20 3000...14 rows selected.

You can sort by a column that is not in the SELECT list.

Summary

SELECT [DISTINCT] {*| column [alias], ...}FROM table[WHERE condition(s)][ORDER BY {column, expr, alias} [ASC|DESC]];