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Retrieving Data Using Retrieving Data Using the SQL the SQL SELECTSELECT Statement Statement

Satrio Agung Wicaksono, S.Kom., M.Kom

ObjectivesObjectives

After completing this lesson, you should be able to do the following:◦ List the capabilities of SQL SELECT statements◦ Execute a basic SELECT statement◦ Limit the rows that are retrieved by a query◦ Sort the rows that are retrieved by a query

Capabilities of SQL Capabilities of SQL SELECTSELECT StatementsStatements

SelectionProjection

Table 1 Table 2

Table 1Table 1

Join

Basic Basic SELECTSELECT Statement Statement

◦ SELECT identifies the columns to be displayed◦ FROM identifies the table containing those columns

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

Selecting All ColumnsSelecting All Columns

SELECT *FROM departments;

Selecting Specific Selecting Specific ColumnsColumns

SELECT department_id, location_idFROM departments;

Writing SQL StatementsWriting SQL Statements

◦SQL statements are not case-sensitive. ◦SQL statements can be on one or more lines.◦Keywords cannot be abbreviated or split

across lines.◦Clauses are usually placed on separate lines.◦ Indents are used to enhance readability.

Arithmetic ExpressionsArithmetic Expressions

Create expressions with number and date data by using arithmetic operators.

Operator Description

+ Add

- Subtract

* Multiply

/ Divide

SELECT last_name, salary, salary + 300FROM employees;

Using Arithmetic Using Arithmetic OperatorsOperators

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SELECT last_name, salary, 12*salary+100FROM employees;

Operator PrecedenceOperator Precedence

SELECT last_name, salary, 12*(salary+100)FROM employees;

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Defining a Null ValueDefining a Null Value

◦ A null is a value that is unavailable, unassigned, unknown, or inapplicable.

◦ A null is not the same as a zero or a blank space.

SELECT last_name, job_id, salary, commission_pctFROM employees;

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SELECT last_name, 12*salary*commission_pctFROM employees;

Null Values Null Values in Arithmetic Expressionsin Arithmetic Expressions

Arithmetic expressions containing a null value evaluate to null.

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Defining a Column AliasDefining a Column Alias

A column alias:◦Renames a column heading◦ Is useful with calculations◦ Immediately follows the column name

(There can also be the optional AS keyword between the column name and alias.)

◦Requires double quotation marks if it contains spaces or special characters or if it is case-sensitive

Using Column AliasesUsing Column Aliases

SELECT last_name "Name" , salary*12 "Annual Salary"FROM employees;

SELECT last_name AS name, commission_pct commFROM employees;

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Concatenation OperatorConcatenation Operator

A concatenation operator:◦ Links columns or character strings to

other columns ◦ Is represented by keyword CONCAT◦ Creates a resultant column that is a

character expression

SELECT concat(last_name,job_id) AS "Employees"FROM employees;

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Literal Character StringsLiteral Character Strings

◦A literal is a character, a number, or a date that is included in the SELECT statement.

◦Date and character literal values must be enclosed by single quotation marks.

◦Each character string is output once for eachrow returned.

Using Literal Character Using Literal Character StringsStrings

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SELECT concat(last_name,' is a ‘,job_id) AS "Employee Details"FROM employees;

Duplicate RowsDuplicate Rows

The default display of queries is all rows, including duplicate rows.

SELECT department_idFROM employees;

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SELECT DISTINCT department_idFROM employees;

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Limiting Rows Using a Limiting Rows Using a SelectionSelection

“retrieve allemployees in department 90”

EMPLOYEES

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Limiting the Rows That Are Limiting the Rows That Are SelectedSelected

◦Restrict the rows that are returned by using the WHERE clause:

◦The WHERE clause follows the FROM clause.

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

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

Using the Using the WHEREWHERE Clause Clause

SELECT last_name, job_id, department_idFROM employeesWHERE last_name = 'Whalen' ;

Character Strings and Character Strings and DatesDates

◦Character strings and date values are enclosed by single quotation marks.

◦Character values are case-sensitive, and date values are format-sensitive.

◦The default date format is yyyy-mm-dd.

Comparison ConditionsComparison Conditions

Operator Meaning

= Equal to

> Greater than

>= Greater than or equal to

< Less than

<= Less than or equal to

<> Not equal to

BETWEEN...AND...

Between two values (inclusive)

IN(set) Match any of a list of values

LIKE Match a character pattern

IS NULL Is a null value

SELECT last_name, salaryFROM employeesWHERE salary <= 3000 ;

Using Comparison Using Comparison ConditionsConditions

SELECT last_name, salaryFROM employeesWHERE salary BETWEEN 2500 AND 3500 ;

Using the Using the BETWEENBETWEEN ConditionCondition

Use the BETWEEN condition to display rows based on a range of values:

Lower limit Upper limit

SELECT employee_id, last_name, salary, manager_idFROM employeesWHERE manager_id IN (100, 101, 201) ;

Using the Using the ININ Condition Condition

Use the IN membership condition to test for values in a list:

SELECT first_nameFROM employeesWHERE first_name LIKE 'S%' ;

Using the Using the LIKELIKE Condition Condition

◦Use the LIKE condition 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.

◦You can combine pattern-matching characters:

◦You can use the ESCAPE identifier to search for the actual % and _ symbols.

SELECT last_nameFROM employeesWHERE last_name LIKE '_o%' ;

Using the Using the LIKELIKE Condition Condition

SELECT last_name, manager_idFROM employeesWHERE manager_id IS NULL ;

Using the Using the NULLNULL Conditions Conditions

Test for nulls with the IS NULL operator.

Logical ConditionsLogical Conditions

Operator Meaning

AND Returns TRUE if both component conditions are true

OR Returns TRUE if either component condition is true

NOT Returns TRUE if the following condition is false

SELECT employee_id, last_name, job_id, salaryFROM employeesWHERE salary >=10000AND job_id LIKE '%MAN%' ;

Using the Using the ANDAND Operator Operator

AND requires both conditions to be true:

SELECT employee_id, last_name, job_id, salaryFROM employeesWHERE salary >= 10000 OR job_id LIKE '%MAN%' ;

Using the Using the OROR Operator Operator

OR requires either condition to be true:

SELECT last_name, job_idFROM employeesWHERE job_id NOT IN ('IT_PROG', 'ST_CLERK', 'SA_REP') ;

Using the Using the NOTNOT Operator Operator

Rules of PrecedenceRules of Precedence

You can use parentheses to override rules of precedence.

Operator Meaning

1 Arithmetic operators

2 Concatenation operator

3 Comparison conditions

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

5 [NOT] BETWEEN

6 Not equal to

7 NOT logical condition

8 AND logical condition

9 OR logical condition

SELECT last_name, job_id, salaryFROM employeesWHERE job_id = 'SA_REP'OR job_id = 'AD_PRES'AND salary > 15000;

Rules of PrecedenceRules of Precedence

SELECT last_name, job_id, salaryFROM employeesWHERE (job_id = 'SA_REP'OR job_id = 'AD_PRES')AND salary > 15000;

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Using the Using the ORDER BYORDER BY ClauseClause

◦Sort retrieved rows with the ORDER BY clause: ASC: ascending order, default DESC: descending order

◦The ORDER BY clause comes last in the SELECT statement:

SELECT last_name, job_id, department_id, hire_dateFROM employeesORDER BY hire_date ;

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SortingSorting

◦ Sorting in descending order:

◦ Sorting by column alias:

◦ Sorting by multiple columns:

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

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SELECT employee_id, last_name, salary*12 annsalFROM employeesORDER BY annsal ;

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SELECT last_name, department_id, salaryFROM employeesORDER BY department_id, salary DESC;

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CASECASE Expression Expression

Facilitates conditional inquiries by doing the work of an IF-THEN-ELSE statement:

CASE expr WHEN comparison_expr1 THEN return_expr1 [WHEN comparison_expr2 THEN return_expr2 WHEN comparison_exprn THEN return_exprn ELSE else_expr]END

SELECT last_name, job_id, salary, CASE job_id WHEN 'IT_PROG' THEN 1.10*salary WHEN 'ST_CLERK' THEN 1.15*salary WHEN 'SA_REP' THEN 1.20*salary ELSE salary END "REVISED_SALARY"FROM employees;

Using the Using the CASECASE Expression ExpressionFacilitates conditional inquiries by doing the work of

an IF-THEN-ELSE statement:

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