SQL – Simple Queries and JOIN

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Database ManagementDatabase Management

Selecting Data From Database

General Form:

SELECT list_of_columns FROM table[s] [WHERE search_conditions]

Choosing all columns:SELECT * FROM table_list;

Examples: SELECT * FROM FACULTY; SELECT * FROM STUDENT;

Selecting Data From Database

Choosing Specific Columns:

SELECT column_name [, column_name] … FROM table_name;

SELECT FacFirstName, FacLastName, FacSalaryFROM Faculty;

Selecting Data From Database

Renaming Columns:

SELECT column_name as column_heading

FROM table_name;

SELECT FacFirstName AS First, FacLastName AS Last, FacSalary AS Salary

FROM Faculty

Selecting Data From Database

Using Expressions:

SELECT FacFirstName, FacLastName, FacCity, FacSalary*1.1 AS IncreasedSalary,

FacHireDate

FROM Faculty;Precedence Hierarchy for Precedence Hierarchy for

Arithmetic OperatorsArithmetic Operators

Parentheses

Multiplication Division

Subtraction Addition

Selecting Data From Database

Comparison Operators:= , <, >, <=, >=, <>

SELECT OfferNo, CourseNo, FacSSN FROM Offering WHERE OffTerm = ‘SPRING’;

SELECT OfferNo, CourseNo, FacSSN FROM OfferingWHERE OffTerm <> ‘FALL’;

Selecting Data From Database

SELECT FacFirstName, FacLastName, FacSSN FROM FacultyWHERE to_number(to_char(FacHireDate, ‘YYYY’)) > 1991;

SELECT FacFirstName, FacLastName, FacCity, FacSalary*1.1 AS IncreasedSalary, FacHireDate FROM Faculty

WHERE to_number(to_char(FacHireDate, 'YYYY')) > 1991

Selecting Data From Database

Boolean OR LOGICAL OPERATORS AND, OR, and NOT:

SELECT FacFirstName, FacLastName, FacSalaryFROM FacultyWHERE FacSalary > 65000 AND FacRank = 'PROF‘;

SELECT OfferNo, CourseNo, FacSSN FROM Offering WHERE (OffTerm = 'FALL' AND OffYear = 1999) OR (OffTerm = 'WINTER' AND OffYear = 2000)

Logical Operator PrecedenceLogical Operator PrecedenceParenthesesParentheses

Multiplication DivisionMultiplication Division

Subtraction AdditionSubtraction Addition

NOTNOT

ANDAND

OROR

Selecting Data From Selecting Data From DatabaseDatabase

Selecting Data From Database

Ranges: With the comparison operators > and < With the keyword BETWEEN

SELECT FacFirstName, FacLastName, FacHireDate FROM Faculty WHERE to_number(to_char(FacHireDate, ‘YYYY’))BETWEEN 1994 AND 1995

SELECT FacFirstName, FacLastName, FacHireDate FROM Faculty WHERE to_number(to_char(FacHireDate, ‘YYYY’)) >= 1994AND to_number(to_char(FacHireDate, ‘YYYY’)) <= 1995

Selecting Data From Database

Lists Using IN and NOT IN:

SELECT StdFirstName, StdLastNAme, StdMajorFROM Student WHERE StdClass IN ('JR', 'SR');

Using IS NULL, NOT NULL:

SELECT OfferNo, CourseNo FROM Offering WHERE FacSSN IS NULL;

Selecting Data From Database

Matching Character Strings Using LIKE: Two wildcard characters for use with LIKE:

% any string of zero or more characters - any single character (Used with %)

SELECT CourseNo FROM Offering WHERE CourseNo LIKE 'IS%‘;

SELECT CourseNo FROM Offering WHERECourseNo LIKE ‘IS_2%’;

Eliminating Duplicate RowsEliminating Duplicate Rows: Distinct and All

DISTINCT returns only those rows that are unique

ALL returns all qualified rows, by default all rows are returned by a SELECT query

SELECT [DISTINCT | ALL] select_list

Distinct combination of items

DISTINCT treats each null in a particular column as a duplicate of all other null values in that column

Eliminating Duplicate Rows

SELECT DISTINCT CourseNo from Offering;

SELECT ALL CourseNo from Offering; (Same as the next statement)

SELECT CourseNo from Offering;

Sorting Data

Use of ORDER BY clause to order/sort the rows from a select query

SELECT select_listFROM table_list[WHERE conditions][ORDER BY {expression [ASC | DESC] | position[ASC | DESC]}[, {expression [ASC | DESC] | position [ASC | DESC] }] …]

Sorting DataMost systems require that each sort element (column or expression) appear in the select list

If multiple columns are specified the sort is done based on the order in which columns are specified

Default sort direction is ASC

NULL will appear at the beginning or the end of the sorted list

Sorting Data

SELECT StdFirstName, StdLastName, StdCity

FROM Student

ORDER BY StdLastName;

SELECT StdClass, StdFirstName, StdLastNAme, StdMajor

FROM Student

WHERE StdClass IN ('JR', 'SR')

ORDER BY StdClass ASC, StdLastName DESC;

Sorting Data

Three options for expressions: Use an integer to represent the expression’s position

in the select list Use a column heading in the select list Use the whole expression

SELECT StdClass, StdFirstName, StdLastNAme, StdMajorFROM Student WHERE StdClass IN ('JR', 'SR')ORDER BY 3 ASC, 1 DESC;

Aggregate Functions

Used to obtain summary values

Aggregate functions always take an argument

General syntax of aggregate functions: aggregate_function ([DISTINCT] expressions)

(You can omit the DISTICT clause)

Aggregate functions are used in conjunction with GROUP BY clause in a SELECT query.

Aggregate Functions

Aggregate FunctionAggregate Function ResultResult

SUM ([DISTINCT] expression) The total of (distinct) values in the numerical expression

AVG([DISTINCT] expression) The average of (distinct) values in the numeric expression

COUNT([DISTINCT] expression) The number of (distinct) non-null values in the expression

COUNT(*) The number of selected rows

MAX(expression) The highest value in the expression

MIN(expression) The lowest value in the expression

Aggregate Functions and Grouping Data

SELECT FacRank, AVG(FacSalary) AS AvgSalaryFROM Faculty GROUP BY FacRank;

SELECT FacRank, Max(FacSalary) AS Maximum_Salary,Min(FacSalary) AS Minimum_SalaryFROM Faculty GROUP BY FacRank;

SELECT CourseNo, Count(DISTINCT FacSSN) AS No_Insructors FROM Offering GROUP BY CourseNo;

Conditions on Grouped Data

Use HAVING to select row that satisfy some condition on grouped data

You can still use WHERE clause to select rows according to some condition WHERE eliminates the rows first and then groups the data HAVING groups first and then eliminates the rows

SELECT StdMajor, AVG(StdGPA) AS AvgGpaFROM Student WHERE StdClass IN ('JR', 'SR')GROUP BY StdMajorHAVING AVG(StdGPA) > 3.1;

Grouping Data Overview

SQL statement processing order SQL statement processing order (adapted from van der Lans, (adapted from van der Lans, p.100)p.100)

Joining TablesMost databases have many tables

Combine tables using the join operator (Inner Join or Outer Join)

Specify matching condition Can be any comparison but usually = PK = FK most common join condition Relationship diagram useful when combining tables Columns being compared should have similar values Join column data types must be compatible Use alias names to improve readability

Joining Tables

Join Types: Equijoin Natural join Self join Outer join

Equijoin: Joining condition is based on equality between

values in the common column Common columns appear (repeat) in the result table

Inner Joins

Joining Tables

Natural Join: Same as equijoin except join column displayed only

once Natural Join may be based on other relational

operators

Self-join: Compares values within a column of a single table

Outer Joins: Rows that do not have matching values in common

columns are included in the result table

Joining Tables

FacSSN FacName 111-11-1111 joe 222-22-2222 sue 333-33-3333 sara

OfferNo FacSSN

1111 111-11-1111 2222 222-22-2222 3333 111-11-1111

FacSSN FacName OfferNo 111-11-1111 joe 1111

222-22-2222 sue 2222

111-11-1111 joe 3333

Faculty

Offering

Natural Join of Offering andFaculty

Joining Tables: Inner join

List Tables in the FROM clause

List conditions in the WHERE clause

SELECT OfferNo, CourseNo, FacFirstName, FacLastName FROM Offering, Faculty WHERE OffTerm = 'FALL' AND OffYear = 1999 AND FacRank = 'ASST' AND CourseNo LIKE 'IS%'AND Faculty.FacSSN = Offering.FacSSN;

Joining Tables: Outer Join

One-Sided Outer joins (using a + sign):

SELECT OfferNo, CourseNo, FacLastName, Faculty.FacSSNFROM Offering, Faculty WHERE Faculty.FacSSN (+) = Offering.FacSSN;

(Starts with all the rows from the Offering Table)

SELECT OfferNo, CourseNo, FacLastName, Faculty.FacSSNFROM Offering, Faculty WHERE Faculty.FacSSN = Offering.FacSSN (+);

(Starts with all the rows from the Faculty Table)

Joining Tables: Outer Join

Full Outer Join: SELECT FacSSN, FacFirstName, FacLastName, FacSalary, StdSSN, StdFirstName, StdLastName, StdGPA FROM Faculty, Student WHERE Student.StdSSN = Faculty.FacSSN (+)

UNION SELECT FacSSN, FacFirstName, FacLastName, FacSalary, StdSSN, StdFirstName, StdLastName, StdGPA FROM Faculty, Student WHERE Student.StdSSN (+) = Faculty.FacSSN

Joining Tables: Outer Join

Mixing Inner and Outer Joins: SELECT OfferNo, Offering.CourseNo, OffTerm, CrsDesc, Faculty.FacSSN, FacLastName FROM Faculty, Course, Offering WHERE Offering.FacSSN = Faculty.FacSSN (+) AND Course.CourseNo = Offering.CourseNo AND Course.CourseNo LIKE 'IS%'

Functions

ORACLE has several functions that you can use:

Arithmetic functions: ABS, CEIL, FLOOR etc.String Manipulation Function: CONCAT, LENGTH, LPAD etc.Date Functions: SYSDATE, ADD_MONHTS, LAST_DATE etc.

More details can be found in your ORACLE Reference Book