SQL: Data Manipulation

Presented by Mary Choi

For CS157B

Dr. Sin Min Lee

Introduction

Structured Query Language (SQL) Writing an SQL Command Retrieving Data Building SQL Statements Performing Database Updates

What is SQL? SQL is an example of a

transform-oriented language. A language designed to use

relations to transform inputs into required outputs.

Source: Database Systems Connolly/Begg

What is SQL? ISO SQL has two major

components: Data Definition Language (DDL) Data Manipulation Language

(DML)

Source: Database Systems Connolly/Begg

Data Definition Language (DDL)

Defining the database structure Tables

Controlling access to the data What a user can legally access

Source: Database Systems Connolly/Begg

Data Manipulation Language (DML)

Retrieving Data Query tables

Updating Data Populate tables

Source: Database Systems Connolly/Begg

Writing SQL Commands

SQL statement consists of reserved words and user-defined words Reserved words are a fixed part

of the SQL language and have a fixed meaning

User-defined words are made up by the user (according to syntax rules)

Source: Database Systems Connolly/Begg

Reserved Words

Are fixed part of the SQL language Have a fixed meaning Require exact spelling Kept on the same line

Source: Database Systems Connolly/Begg

User-defined Words

Are made up by the user Governed by a set of syntax rules Represent names of database

objects such as: Tables Columns Views Indexes

Source: Database Systems Connolly/Begg

Data Manipulation

Select: query data in the database Insert: insert data into a table Update: updates data in a table Delete: delete data from a table

Source: Database Systems Connolly/Begg

Literals

Non-numeric data values must be enclosed in single quotes: ’16 Holland Drive’ ‘CS157B’

Numeric data values must NOT be enclosed in single quotes: 6 600.00

Source: Database Systems Connolly/Begg

Writing SQL Commands

Most components of an SQL statement are case insensitive, but one exception is that literal character data must be typed exactly as it appears in the database.

Source: Database Systems Connolly/Begg

Simple Query

Select specifies which columns are to appear in the output.

From specifies the table(s) to be used.

Where filters the rows subject to some condition(s).

Source: Database Systems Connolly/Begg

Simple Query

Group By forms groups of rows with the same column value.

Having filters the groups subject to some condition.

Order By specifies the order of the output.

Source: Database Systems Connolly/Begg

Retrieve all columns and all rows

SELECT firstColumn,…,lastColumn

FROM tableName;

SELECT *

FROM tableName;

Use of Distinct

SELECT DISTINCT columnName

FROM tableName;

columnName

A

B

C

D

columnName

A

A

B

B

C

D

Calculated fields

SELECT columnName/2

FROM tableName

price

5.00

3.00

6.00

price

10.00

6.00

12.00

Comparison Search Condition

= equals

< > is not equal to (ISO standard)

!= “ “ “ “ (allowed in some dialects)

< is less than

> is greater than

<= is less than or equal to

>= is greater than or equal to

Source: Database Systems Connolly/Begg

Comparison Search Condition

An expression is evaluated left to right.

Subexpressions in brackets are evaluated first.

NOTs are evaluated before ANDs and ORs.

ANDs are evaluated before ORs.

Source: Database Systems Connolly/Begg

Range Search ConditionSELECT columnNameFROM tableNameWHERE columnName BETWEEN 20

AND 30;

SELECT columnNameFROM tableNameWHERE columnName >= 20 AND columnName <= 30;

Set membership search condition

SELECT columnName

FROM tableName

WHERE columnName

IN (‘name1’, ‘name2’);

SELECT columnName

FROM tableName

WHERE columnName = ‘name1’

OR columnName = ‘name2’;

Pattern matching symbols

% represents any sequence of zero

or more characters (wildcard).

_ represents any single character

Source: Database Systems Connolly/Begg

Pattern match search condition‘h%’ : begins with the character h .

‘h_ _ _’ : four character string beginning with the character h.

‘%e’ : any sequence of characters, of length at least 1, ending with the character e.

‘%CS157B%’ : any sequence of characters of any length containing CS157B

Source: Database Systems Connolly/Begg

Pattern match search condition

LIKE ‘h%’

begins with the character h .

NOT LIKE ‘h%’

does not begin with the character h.

Source: Database Systems Connolly/Begg

Pattern match search condition

To search a string that includes a

pattern-matching character

‘15%’

Use an escape character to represent

the pattern-matching character.

LIKE ‘15#%’ ESCAPE ‘#’

Source: Database Systems Connolly/Begg

NULL search condition

DOES NOT WORK

comment = ‘ ’

comment != ‘ ’

DOES WORK

comment IS NULL

comment IS NOT NULL

Sorting

The ORDER BY clause consists of list of column

identifiers that the result is to be sorted on, separated by commas.

Allows the retrieved rows to be ordered by ascending (ASC) or descending (DESC) order

Source: Database Systems Connolly/Begg

Sorting

Column identifier may be A column name A column number (deprecated)

Source: Database Systems Connolly/Begg

Sorting

SELECT type, rent

FROM tableName

ORDER BY type, rent ASC;

Source: Database Systems Connolly/Begg

type rent

Apt

Apt

Flat

Flat

450

500

600

650

type rent

Flat

Apt

Flat Apt

650 450

600 500

Aggregate Functions

COUNT returns the number … SUM returns the sum … AVG returns the average … MIN returns the smallest … MAX returns the largest …

value in a specified column.

Source: Database Systems Connolly/Begg

Use of COUNT( * )

How many students in CS157B?

SELECT COUNT( * ) AS my count

FROM CS157B

my count

40

GROUP BY clause

When GROUP BY is used, each item in the SELECT list must be single-valued per group.

The SELECT clause may contain only Column names Aggregate functions Constants An expression involving combinations of the

above

Source: Database Systems Connolly/Begg

GroupingSELECT dept, COUNT(staffNo) AS my count

SUM(salary)

FROM tableName

GROUP BY dept

ORDER BY dept

dept my count

Salary

A

B

C

2

2

1

300.00300.00 200.00

dept staffNo Salary

A

B

C

A

B

1

1

1

2

2

200.00

200.00

200.00

100.00

100.00

Restricting Grouping

HAVING clause is with the GROUP BY clause. filters groups into resulting table. includes at least one aggregate

function. WHERE clause

filters individual rows into resulting table.

Aggregate functions cannot be used.

Source: Database Systems Connolly/Begg

SELECT dept, COUNT(staffNo) AS my count, SUM(salary) AS my sum

FROM StaffGROUP BY deptHAVING COUNT(staffNo) > 1ORDER BY dept;

Source: Database Systems Connolly/Begg

dept my count

my sum

A

B

2

2

300.00 300.00

dept staffNo Salary

A

B

C

A

B

1

1

1

2

2

200.00

200.00

200.00

100.00

100.00

Subqueries

SELECT columnNameA

FROM tableName1

WHERE columnNameB = (SELECT columnNameB

FROM tableName2

WHERE condition);

Source: Database Systems Connolly/Begg

result from inner SELECT applied as a condition for the outer SELECT

Subquery with Aggregate Function

SELECT fName, salary –

( SELECT AVG(salary)

FROM Staff ) AS salDiff

FROM Staff

WHERE salary > ( SELECT AVG(salary)

FROM Staff );

Source: Database Systems Connolly/Begg

List all staff whose salary is greater than the average salary,show by how much their salary is greater than the average.

Nested Subqueries: Use of IN

SELECT propertyFROM PropertyForRentWHERE staff IN(

SELECT staffFROM StaffWHERE branch = (

SELECT branch FROM Branch WHERE street = ‘112 A St’));

Source: Database Systems Connolly/Begg

Selects branch at 112 A St

Nested Subqueries: Use of IN

SELECT property

FROM PropertyForRent

WHERE staff IN(

SELECT staff

FROM Staff

WHERE branch = ( branch ) );

Source: Database Systems Connolly/Begg

Select staff members who works at branch.

Nested Subqueries: Use of IN

SELECT property

FROM PropertyForRent

WHERE staff IN( staffs who works

at branch on ‘112 A St’);

Source: Database Systems Connolly/Begg

Since there are more than one row selected, “=“ cannot be used.

Use of ANY/SOME

SELECT name, salary

FROM Staff

WHERE salary > SOME( SELECT salary

FROM Staff

WHERE branch = ‘A’ );

Source: Database Systems Connolly/Begg

Result:{2000,3000,4000}

Result: {list of staff with salary greater than 2000.}

Use of ALL

SELECT name, salary

FROM Staff

WHERE salary > ALL( SELECT salary

FROM Staff

WHERE branch = ‘A’ );

Source: Database Systems Connolly/Begg

Result:{2000,3000,4000}

Result: {list of staff with salary greater than 4000.}

Use of Any/Some and All

If the subquery is empty: ALL returns true ANY returns false

ISO standard allows SOME to be

used interchangeably with ANY.

Source: Database Systems Connolly/Begg

Multi-Table Queries

Join Inner Join Left Outer Join Right Outer Join Full Outer Join

Source: Database Systems Connolly/Begg

JoinSELECT client

FROM Client c, View v

WHERE c.client = v.client;

Source: Database Systems Connolly/Begg

FROM Client c JOIN View v ON c.client = v.client(creates two identical client columns)

FROM Client JOIN View USING clientFROM Client NATURAL JOIN View

ISO standard Alternatives

Join

The join operation combines data from two tables by forming pairs of related rows where the matching columns in each table have the same value.

If one row of a table is unmatched, the row is omitted from the resulting table.

Source: Database Systems Connolly/Begg

Inner Join

Source: Database Systems Connolly/Begg

SELECT b.*,p.*

FROM Branch b, Property p

WHERE b.bCity = p.pCity;

branch bcity

B003

B004

B002

Glasgow

Bristol

London

property pcity

P103

P204

P102

Aberdeen

London Glasgow

Inner Join Result

Source: Database Systems Connolly/Begg

SELECT b.*,p.*

FROM Branch b, Property p

WHERE b.bCity = p.pCity;

branch bcity

B003

B002

Glasgow

London

property pcity

P102

P204

Glasgow

London

Left Outer Join

SELECT b.*,p.*

FROM Branch b

LEFT JOIN Property p

ON b.bCity = p.pCity;

Source: Database Systems Connolly/Begg

branch bcity

B003

B004

B002

Glasgow

Bristol

London

property pcity

P102

NULL

P204

Glasgow NULL

London

Right Outer Join

SELECT b.*,p.*

FROM Branch b

RIGHT JOIN Property p

ON b.bCity = p.pCity;

Source: Database Systems Connolly/Begg

property pcity

P103

P204

P102

Aberdeen

London Glasgow

branch bcity

NULL

B002

B003

NULL

London Glasgow

Full Outer JoinSELECT b.*,p.*

FROM Branch b

FULL JOIN Property p

ON b.bCity = p.pCity;

Source: Database Systems Connolly/Begg

branch bcity

B004

NULL

B002

B003

Bristol

NULL

London Glasgow

property pcity

NULL

P103

P204

P102

NULL

Aberdeen

London Glasgow

Exists and Not Exists

For use only with subqueries. Produces true/false results.

Source: Database Systems Connolly/Begg

EXISTS returns true IFF there exists at

least one row in the resulting table returned by the subquery

Source: Database Systems Connolly/Begg

NOT EXISTS returns false if the subquery is

empty.

Exists and Not Exists

SELECT staff

FROM Staff s

WHERE EXISTS( SELECT *

FROM Branch b

WHERE s.branch = b.branch

AND city = ‘London’);

Source: Database Systems Connolly/Begg

Find all staff who work in a London branch office.

Combining Result Tables

UNION INTERSECT EXCEPT

Source: Database Systems Connolly/Begg

R S R S R – S

R

S S S

RR

Use of UNION

( SELECT city

FROM Branch

WHERE city IS NOT NULL)

UNION

( SELECT city

FROM Property

WHERE city IS NOT NULL);

Source: Database Systems Connolly/Begg

city

London

Glasgow

Aberdeen

Bristol

List of all cities where there is either a branch or property.

Use of INTERSECT

( SELECT city FROM Branch )

INTERSECT

( SELECT city FROM Property );

Source: Database Systems Connolly/Begg

city

London

Glasgow

Aberdeen

List of all cities where there is both a branch and a property.

Use of EXCEPT

( SELECT city FROM Branch )

EXCEPT

( SELECT city FROM Property );

Source: Database Systems Connolly/Begg

city

Bristol

List of all cities where there is a branch office but no properties.

Database Updates

INSERT Adds new rows of data to a table

UPDATE Modifies existing data in a table

DELETE Removes rows of data from a table

Source: Database Systems Connolly/Begg

Use of INSERT

INSERT INTO TableName[(columnList)]

VALUES (dataValueList)

Source: Database Systems Connolly/Begg

Use of UPDATE

UPDATE TableName

SET columnnName1 = dataValueList

[, columnName2 = dataValue2…]

[WHERE searchCondition]

Source: Database Systems Connolly/Begg

Use of DELETE

DELETE FROM TableName

[WHERE searchCondition]

Source: Database Systems Connolly/Begg