1

Chapter 8a

Objectives: to learn

• the relational set

operators – UNION,

– UNION ALL,

– INTERSECT, and

– MINUS

• How to create and use

Sequence objects as

an ‘autonumber’

• SQL functions to

manipulate dates,

strings, and other data

Outline

• Relational Set

Operators

• SEQUENCE Objects

• SQL Built-in Functions – Numeric

– String

– Date

– Misc

– Pseudo Columns

1Fall 2010 - CS275

Relational Set Operators

• Based on relational algebra/ set operations

• Work properly if relations are union-compatible

– Names of relation attributes must be the same and

their data types must be identical

• SQL-’99 ANSI Standard commands

– UNION

– INTERSECT

– MINUS (called ‘EXCEPT’ in the 99 standards)

• Some DMS’s may not implement these.

2Fall 2010 - CS275

UNION

• Combines tables eliminating duplicate rows.

• Can be used to unite more than two queriesSELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE, CUS_PHONE

FROM CUSTOMER

UNION

SELECT CUS_LNAME, CUS_FNAME,CUS_INITIAL,

CUS_AREACODE, CUS_PHONE

FROM CUSTOMER_2;

3Fall 2010 - CS275

UNION ALL

• Combines tables retaining duplicate rows.SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE, CUS_PHONE

FROM CUSTOMER

UNION ALL

SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE, CUS_PHONE

FROM CUSTOMER_2;

4Fall 2010 - CS275

2

INTERSECT

• Combines rows from two queries, returning only

the rows that appear in both sets.

• Example:SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

FROM CUSTOMER

INTERSECT

SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE, CUS_PHONE

FROM CUSTOMER_2;

5Fall 2010 - CS275

INTERSECT

SELECT CUS_CODE

FROM CUSTOMER WHERE CUS_AREACODE = ‘615’

INTERSECT SELECT DISTINCT CUS_CODE

FROM CUSTOMER;

6Fall 2010 - CS275

Syntax Alternatives - Intersect

• Generalized Syntax:

Select <columns>

from t1 where t1.fieldA in (select t2.fieldA from t2);

• Example: solving the previous problem:

Select cus_code

from customer

where cus_areacode = ‘615’ and

cus-code in (select distinct cus_code from

Invoice)

7Fall 2010 - CS275

MINUS

• Combines rows from two queries, returning only

the rows that appear in the first set but not in the

second

– Example:

SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE,

FROM CUSTOMER

MINUS

SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE,

FROM CUSTOMER_2

8Fall 2010 - CS275

3

MINUS

9

Example reversing the tables:SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE, CUS_PHONE FROM CUSTOMER_2MINUSSELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL,

CUS_AREACODE, CUS_PHONE FROM CUSTOMER

Fall 2010 - CS275

Syntax Alternatives -Minus

• Generalized Syntax

Select <columns> from t1 where t1.key not in (select

t2.key from t2);

• Example starting with previous problem, but using

another table(non-union compatiable):Select cus_code from customer

where cus_areacode = ‘615’ and cus_code not in

(select distinct cus_code from Invoice);

• IN and NOT IN subqueries can be used in place of INTERSECT & MINUS

10Fall 2010 - CS275

Oracle Sequences

• Sequence Numbers: allows establishing an

“autonumber” sequence

• Oracle sequences

– Independent object in the database

– Are named and used anywhere a numeric value is

expected

– Not tied to a table or column

– Generates new numeric values that can be

assigned to any column in any table

– A named sequence can be created and deleted at

any time11Fall 2010 - CS275

Oracle Sequence

• Create sequence <seq_name> start with <n>

Increment by <n>;

– Examples:

Create sequence cust_code start with 100

increment by 1;

Create sequence product_num NOCACHE;

• Viewing your sequences

Select * from user_sequences;

12Fall 2010 - CS275

4

Oracle Sequence

Create sequence cus_code_seq start with 20010

nocache;

Create sequence inv_number_seq start with 4010

nocache;

13Fall 2010 - CS275

Oracle Sequence

• Sequence numbers are used via a keyword– NEXTVAL

• used to generate a new number

• Often used as a primary key for a table row

• Example:

Insert into table invoice values

(inv_sequence.NEXTVAL, 20010, sysdate);

– CURRVAL• Used to retrieve the current value of the sequence.

• Cannot directly retrieve attributes from a sequence.

• Example:

Select inv_sequence.CURRVAL from dual;

14Fall 2010 - CS275

Oracle Sequences

Insert into customer values ( cus_code_seq.nextval, ‘Connery’, ‘Sean’, NULL, ‘615’, ‘898-2007’, 0.00);

Insert into Invoice values ( inv_number_seq.nextval, 20010, sysdate);

Insert into Line values (inv_number_seq.currval, 1, ’13-Q2/P2’, 1, 14.99);

Insert into line values( inv_number_seq.currval, 2,

‘23109-HB’, 1, 9.95);

15

inserting a series of rows with auto sequence

numbers.

Fall 2010 - CS275

SQL (non-aggregate) Functions

• Functions manipulate data items and return a

single result. (i.e. SQL functions are similar to

functions in programming languages.)

• Oracle has more than 150 different functions. (See

link on our resource page to the Oracle

documentation )

• Functions use numerical, date, or string values, which may be part of a command or a table attribute.

• The Function may appear anywhere in an SQL statement

16Fall 2010 - CS275

5

Numeric Functions

• Grouped in different

ways

– Algebraic,

trigonometric,

logarithmic, etc.

• Do not confuse with

aggregate functions

– Aggregate functions

operate over sets

– Numeric functions

operate over single row

17Fall 2010 - CS275

SQL Functions - Numeric

ABS(n) -Absolute value of n

CEIL(n) -Smallest integer greater or equal to n

FLOOR(n) -Largest integer equal to or less than n

MOD(m,n) -Remainder of m divided by n

POWER(m,n) -m raised to the nth power

ROUND(n,[m]) -n rounded to m decimal places.

SIGN(n) -If n<0 returns -1, if n= 0 returns 0, if

n>0 returns 1

SQRT(n) -Square root of n, if n<0 returns NULL

TRUNC(c[m]) -n truncated to m decimal places

18Fall 2010 - CS275

String Functions

19

• The most used functions are the String functions

• Examples:Upper/LowerSubstrLength|| - or Concat

Fall 2010 - CS275

SQL Functions - String

ASCII(str)

CHR(n)

CONCAT(str1,str2)

INITCAP(str)

INSTR(str1,str2[,n[m]])

SUBSTR(str, start, length)

LENGTH(str)

LOWER(str)

L/RPAD(str1,n[,str2])

– Returns ASCII value of first character in str

– Character with ASCII value n

– Returns the combined data items.

– Capitalizes the first letter of each word

– Returns the position of the mthoccurrence

of str2, begins search at position n.

– Returns substring of str

– Returns the length of str

– Forces all letters to lower case

– Left or Right pads str1 to length n with

sequence of characters in str2 (if

unspecified, pads with blanks)

20Fall 2010 - CS275

6

SQL Functions – String

L/RTRIM(str,set)

REPLACE(str,’literal1’,’literal2’)

SOUNDEX(str)

SUBSTR(str,m[,n])

TRANSLATE(str,frm,to)

UPPER(str)

USERENV(str)

– Removes characters starting from the Left or

Right in str up to the first character not in

set.

– Search str for 1st string and replace w/2nd

string. Similar to translate.

– Returns a str value representing the sound of

the word(s) in str.

– Returns substring of str, beginning at

character m, for length of n.

– str is translated from the character set frm

to the character set to.

– Forces all letters to upper case.

– Returns user information for writing audit

trails.21Fall 2010 - CS275

SQL Functions – Date & Time

• All SQL-standard DBMSs support date and time functions

• Date functions take one parameter

• Commonly used Functions:

22

ADD_MONTHS(d,n)

LAST_DAY(d)

MONTHS_BETWEEN(d,e)

NEW_TIME(d,a,b)

NEXT_DAY(d,char)

TRUNC(date)

– Date d plus n months

– Date of last day of month containing d

– Number of months between dates d & e

– Date and time in timezone b when d is

from timezone a.

– Date of first day of week named by char

=> d

– Date with time of day removed. Fall 2010 - CS275

SQL Functions - Data Conversions

CHARTOROWID(char)

HEXTORAW(char)

RAWTOHEX(raw)

ROWIDTOCHAR(rowid)

TO_CHAR(expr[,fmt])

TO_DATE(char[,fmt])

TO_DATE(n, fmt)

TO_NUMBER(char)

– Converts char to a row ID

– Converts char, which must contain a

hexadecimal number to a binary value

– Converts raw to char value containing a

hex number.

– Converts a row ID to a char value

– Converts expr, a number or date value to

a char value. Format may be used to

convert dates.

– Converts from char value to a date value.

fmt specifies the format of the parameter

char

– Converts a number into a date

– Converts a char value to a number.

23Fall 2010 - CS275

Data Conversion Examples

24

TO_DATE :using character

formats to return a date.

TO_CHAR: using a date and

returning pieces of the date

as character values.

Fall 2010 - CS275

7

Data Conversion Examples

25

TO_CHAR: converting a number to a

character string

TO_NUMBER: converting a character

string to a number

NVL: converts a null to a string

DECODE: returns associated value

when matched or a default value

Fall 2010 - CS275

SQL Functions - Miscellaneous

• Misc. Functions- data type on item returned is variable

DECODE (expr, search1, return1, search2, return2,…[default])

If expr equals any search, returns the

following return;

if not, returns default

DUMP (expr[, radix[,start-positions[,bytes]]])

Display the contents of internal data areas

GREATEST (expr,expr,..) Returns greatest of a list of values

LEAST (expr,expr,…) Returns the least of a list of values

NVL (expr1,expr2) If expr1 is null, returns expr2; if expr1 is not

null, returns expr1

VSIZE (expr) Returns the number of bytes in ORACLE’s

internal representation of expr

26Fall 2010 - CS275

SQL Functions -Pseudo-Columns

Level - 1 for root node, 2 for child - used in

..Select...Connect By

Null - Returns a null value - used in Insert

statements for blank data

RowID - ID for each row in a table

RowNum - Order in which the row was extracted

Sysdate - Current date and time

UID - User ID

USER - Name of current user (Login name)

27Fall 2010 - CS275

Chapter 8A Summary

• Relational set operators combine output of two

queries to generate new relation

• Set operations using the key words UNION,

UNION ALL, INTERSECT, and MINUS are part of

the new SQL-’99 extensions.

• Oracle sequences may be used to generate values

to be assigned to a record

• SQL functions are used to extract or transform

data

• SQL has Numeric, String (Character), Date,

Misc./Conversion functions, and Pseudo columns28

Fall 2010 - CS275