e computer notes - Restricting and Sorting Data

8/3/2019 e computer notes - Restricting and Sorting Data

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Restricting and Sorting Data



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Objectives

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

" Limit the rows retrieved by a query"Sort the rows retrieved by a query



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Limiting the Rows Selected

" Restrict the rows returned by using theWHEREclause.

SELECT *|{[DISTINCT] column|expression [alias],...}

FRO M table

[WHERE condition(s)];

" TheWHEREclause follows theFROM clause.



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Using theWHEREClause

SELECT employee_id, last_name, job_id, department_idFROM employeesWHERE department_id = 90 ;



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Character Strings and Dates

"Character strings and date values are enclosed insingle quotation marks.

"Character values are case sensitive, and datevalues are format sensitive.

"The default date format is DD-MON-RR.

SELECT last_name, job_id, department_id

FROM employees

WHERE last_name = 'Whalen';



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Comparison Conditions

Operator Meaning

= Equal to

> Greater than

>= Greater than or equal to

< Less than


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Using Comparison Conditions

SELECT last_name, salary

FROM employees

WHERE salary


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Other Comparison Conditions

Operator Meaning

BETWEEN Between two values (inclusive),

...AND...

IN(set) Match any of a list of values

LIKE Match a character pattern

IS NULL Is a null value



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Using theBETWEENCondition

Use theBETWEENcondition to display rows based ona range of values.

SELECT last_name, salary

FROM employees

WHERE salary BETWEEN 2500 AND 3500;

Lower limit Upper limit



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Using theINCondition

Use theINmembership condition to test for values ina list.

SELECT employee_id, last_name, salary, manager_id

FROM employees

WHERE manager_id IN (100, 101, 201);



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Using theLIKECondition

" Use theLIKEcondition to perform wildcardsearches of valid search string values.

" Search conditions can contain either literalcharacters or numbers:

%denotes zero or many characters.

_ denotes one character.

SELECT first_name

FRO M employees

WHERE first_name LIKE 'S%';



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Using theLIKECondition

"You can combine pattern-matching characters.SELECT last_name

FROM employees

WHERE last_name LIKE '_o%';

"You can use the ESCAPE identifier to search for theactual%and_symbols.


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Using theNULLConditions

Test for nulls with theIS NULLoperator.

SELECT last_name, manager_id

FROM employees

WHERE manager_id IS NULL;



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Logical Conditions

MeaningOperator

ReturnsTRUEifbothcomponentAND

conditions are true

ORReturnsTRUEifeithercomponent

condition is true

NOT ReturnsTRUEif the following

condition is false



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Using theANDOperator

ANDrequires both conditions to be true.

SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary >=10000 AND

job_id LIKE '%MAN%';



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Using theOROperator

ORrequires either condition to be true.

SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary >= 10000 ORjob_id LIKE '%MAN%';



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Using theNOTOperator

SELECT last_name, job_id

FROM employees

WHERE job_id

NOT IN ('IT_PROG', 'ST_CLERK', 'SA_REP');



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Rules of Precedence

Order Evaluated Operator

1 Arithmetic operators

2 Concatenation operator

3 Comparison conditions

4 IS [NOT] NULL,LIKE,[NOT]

5 [NOT] BETWEEN

6 NOTlogical condition

7 ANDlogical condition

8 ORlogical condition

Override rules of precedence by using parentheses.



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Rules of Precedence

SELECT last_name, job_id, salary

FROM employees

WHERE job_id = 'SA_REP'

OR job_id = 'AD_PRES'

AND salary > 15000;


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Rules of Precedence

Use parentheses to force priority.

SELECT last_name, job_id, salary

FROM employees

WHERE (job_id ='SA_REP' OR job_id ='AD_PRES')AND salary > 15000;


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ORDER BYClause

"Sort rows with the ORDER BY clauseASC: ascending order, default

DESC: descending order

" TheORDER BYclause comes last in theSELECTstatement.

SELECT last_name, job_id, department_id,hire_date FROM employees

ORDER BY hire_date ;


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Sorting in Descending Order

SELECT last_name, job_id, department_id,hire_date FROM employeesORDER BY hire_date DESC ;


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Sorting by Column Alias

SELECT employee_id, last_name, salary*12 annsal

FROM employees

ORDER BY annsal;


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Sorting by Multiple Columns

" The order ofORDER BYlist is the order of sort.SELECT last_name, department_id, salary

FROM employees

ORDER BY department_id, salary DESC;


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e computer notes - Restricting and Sorting Data