sql: data manipulation

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)


Data Definition Language (DDL)

Defining the database structure Tables

Controlling access to the data What a user can legally access


Data Manipulation Language (DML)

Retrieving Data Query tables

Updating Data Populate tables


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)


Reserved Words

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


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


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


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


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.


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).


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.


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


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.


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


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


Pattern match search condition

LIKE ‘h%’

begins with the character h .

NOT LIKE ‘h%’

does not begin with the character h.


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 ‘#’


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


Sorting

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


Sorting

SELECT type, rent

FROM tableName

ORDER BY type, rent ASC;


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.


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


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.


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

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


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);


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 );


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’));


Selects branch at 112 A St


SELECT property

FROM PropertyForRent

WHERE staff IN(

SELECT staff

FROM Staff

WHERE branch = ( branch ) );


Select staff members who works at branch.


SELECT property

FROM PropertyForRent

WHERE staff IN( staffs who works

at branch on ‘112 A St’);


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’ );


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’ );


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.


Multi-Table Queries

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


JoinSELECT client

FROM Client c, View v

WHERE c.client = v.client;


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.


Inner Join


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


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;


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



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



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.


EXISTS returns true IFF there exists at

least one row in the resulting table returned by the subquery


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’);


Find all staff who work in a London branch office.

Combining Result Tables

UNION INTERSECT EXCEPT


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);


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 );


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 );


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


Use of INSERT

INSERT INTO TableName[(columnList)]

VALUES (dataValueList)


Use of UPDATE

UPDATE TableName

SET columnnName1 = dataValueList

[, columnName2 = dataValue2…]

[WHERE searchCondition]


Use of DELETE

DELETE FROM TableName

[WHERE searchCondition]


sql: data manipulation

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