INSS 651 1

Lecture 5

SQL Continued

INSS 651 2

SUBQUERIES.

Queries inside queryThere are times when you need information from a table to answer query related to the same table or another table

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Format:SQL>SELECT ….FROM WHERE colname1condition(SELECT col2 . . (SELECT . . ))

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List customers whose balance is greater than the average balance of all customers

Logic:

• To answer this query we need to know average balance of all customers

• We will have to put this in a sub query

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List customers whose balance are greater than the average balance of all customers

SQL> select *

from customer

where cust_balance >

(Select avg(cust_balance)

From customer);

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give the customer balance of customer whose order is 123Logic:

Before we can find balance of customer whose order is 123 we need to find the cust_numb first

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JOINING TABLES

when information needed is in more than one table, we need to join tables;

WHERE clause in the select SQL statement creates a join. Note some queries can also be answered using sub query

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Rules FOR joining

WHERE attribute1 condition attribute2

Ex: where employee.ssn=student.ssn

Value(s) from one table are matched value(s) from other tables all matching values are attached

allows joining of tables based on common attribute domains

without the WHERE clause it will produce a Cartesian product also

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Give the names of salesperson and their customers in maryland

SQL>Select cust_name, Sales_name from Customer C, salesperson Swherec.sales_numb= s. sales_numb’AndUpper(c.cust_st) =‘MD’;

C & S are aliases for tables Customer and Salesperson respectively

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BUILT-IN-FUNCTIONS

• AVG(value)• MAX(value)• MIN(value)• SUM(value)• STDDEV(value)• VARIANCE(value)• COUNT(value)• Etc…

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Nested functions

Select max (avg(grades)) etc..is allowed

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String functions

Several strings can be concatenated

Use string1||string 2

|| implies +

select custname|| ‘,’ || cust_street as address

From customer;

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Substrings

Returns substrings

Format:

Substr(stringvalue,m,n)

Where m is the starting value and n is the length of characters

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Assume orders have the format:”

Abc1234

cdf2345etc..

Get the first and last part of the order

Select substr (order_numb, 1,3),substr (order_numb,4,4)

From order;

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Product (p_code, P_price) table• P_CODE P_PRICE• -------- ----------• 11QER/31 109.99• 13-Q2/P2 14.99• 14-Q1/L3 17.49• 1546-QQ2 39.95• 1558-QW1 43.99• 2232/QTY 109.92• 2232/QWE 99.87• 2238/QPD 38.95• 23109-HB 9.95• 23114-AA 14.4• 54778-2T 4.99

• P_CODE P_PRICE• -------- ----------• 89-WRE-Q 256.99• PVC23DRT 5.87• SM-18277 6.99• SW-23116 8.45• WR3/TT3 119.95

• 16 rows selected.

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Select three characters of price• SQL> select substr(p_price,1,3) from product;

• SUB• ---• 109• 14.• 17.• 39.• 43.• 109• 99.• 38.• 9.9• 14.• 4.9

• SUB• ---• 256• 5.8• 6.9• 8.4• 119

• 16 rows selected.

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Padding charactersRpad (string, length,’set’)Lpad (string,length,’set’)

1* select rpad (p_code,15,'.') as rightpad,p_price from product• SQL> /

• RIGHTPAD P_PRICE• --------------- ----------• 11QER/31....... 109.99• 13-Q2/P2....... 14.99• 14-Q1/L3....... 17.49• 1546-QQ2....... 39.95• 1558-QW1....... 43.99• 2232/QTY....... 109.92• 2232/QWE....... 99.87• 2238/QPD....... 38.95• 23109-HB....... 9.95• 23114-AA....... 14.4• 54778-2T....... 4.99

• RIGHTPAD P_PRICE• --------------- ----------• 89-WRE-Q....... 256.99• PVC23DRT....... 5.87• SM-18277....... 6.99• SW-23116....... 8.45• WR3/TT3 ....... 119.95

• 16 rows selected.

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Length of string

formatlength (string)

Returns length of the string

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SQL> select P_code, length(P_code) from product;

• P_CODE LENGTH(P_CODE)• -------- --------------• 11QER/31 8• 13-Q2/P2 8• 14-Q1/L3 8• 1546-QQ2 8• 1558-QW1 8• 2232/QTY 8• 2232/QWE 8• 2238/QPD 8• 23109-HB 8• 23114-AA 8• 54778-2T 8

• P_CODE LENGTH(P_CODE)• -------- --------------• 89-WRE-Q 8• PVC23DRT 8• SM-18277 8• SW-23116 8• WR3/TT3 8

• 16 rows selected.

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Trimming data

LTrim, Rtrim..remove unwanted characters

Format:

RTRIM (string, ‘set’)

Ltrim (string, ‘set’)

Set is the collection of characters you want to trim

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SQL> select P_code, length(rtrim (P_code,' '))

from product;

• P_CODE LENGTH(RTRIM(P_CODE,''))• -------- ------------------------• 11QER/31 8• 13-Q2/P2 8• 14-Q1/L3 8• 1546-QQ2 8• 1558-QW1 8• 2232/QTY 8• 2232/QWE 8• 2238/QPD 8• 23109-HB 8• 23114-AA 8• 54778-2T 8

• P_CODE LENGTH(RTRIM(P_CODE,''))• -------- ------------------------• 89-WRE-Q 8• PVC23DRT 8• SM-18277 8• SW-23116 8• WR3/TT3 7

• 16 rows selected.

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Remove . From price• SQL> select ltrim(p_price,'.'), p_code from product;

• LTRIM(P_PRICE,'.') P_CODE• ---------------------------------------- --------• 109.99 11QER/31• 14.99 13-Q2/P2• 17.49 14-Q1/L3• 39.95 1546-QQ2• 43.99 1558-QW1• 109.92 2232/QTY• 99.87 2232/QWE• 38.95 2238/QPD• 9.95 23109-HB• 14.4 23114-AA• 4.99 54778-2T

• LTRIM(P_PRICE,'.') P_CODE• ---------------------------------------- --------• 256.99 89-WRE-Q• 5.87 PVC23DRT• 6.99 SM-18277• 8.45 SW-23116• 119.95 WR3/TT3

• 16 rows selected.

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INSTR function

Allows searching for a string of characters, gives the position of the string but does Not cut off anything

Format:

Instr(string, start,occurrence)Start is the start of the stringOccurrence is the position of occurrence

that you want to search

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Search for first “/” in p_code

SQL> select p_code, instr(p_code,'/') from product;;

• P_CODE INSTR(P_CODE,'/')• -------- -----------------• 11QER/31 6• 13-Q2/P2 6• 14-Q1/L3 6• 1546-QQ2 0• 1558-QW1 0• 2232/QTY 5• 2232/QWE 5• 2238/QPD 5• 23109-HB 0• 23114-AA 0• 54778-2T 0

• P_CODE INSTR(P_CODE,'/')• -------- -----------------• 89-WRE-Q 0• PVC23DRT 0• SM-18277 0• SW-23116 0• WR3/TT3 4

• 16 rows selected.

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Separate P_code in two parts: before _ and after _ for names that contain -

SQL> select p_code, substr(P_code, 1, instr(p_code,'/')) part1from product where p_code like '%/%';• 2 3• P_CODE PART1• -------- --------• 11QER/31 11QER/• 13-Q2/P2 13-Q2/• 14-Q1/L3 14-Q1/• 2232/QTY 2232/• 2232/QWE 2232/• 2238/QPD 2238/• WR3/TT3 WR3/

• 7 rows selected.

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SQL> select p_code, substr(P_code, 1, instr(p_code,'/')-1) part1from productwhere p_code like '%/%'; 2 3• P_CODE PART1• -------- --------• 11QER/31 11QER• 13-Q2/P2 13-Q2• 14-Q1/L3 14-Q1• 2232/QTY 2232• 2232/QWE 2232• 2238/QPD 2238• WR3/TT3 WR3

• 7 rows selected.

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Get the right partSQL> select p_code, substr(P_code, instr(p_code,'/')) part2from productwhere p_code like '%/%'; 2 3

• P_CODE PART2• -------- --------• 11QER/31 /31• 13-Q2/P2 /P2• 14-Q1/L3 /L3• 2232/QTY /QTY• 2232/QWE /QWE• 2238/QPD /QPD• WR3/TT3 /TT3

• 7 rows selected.

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SQL> select p_code, substr(P_code, instr(p_code,'/')+1) part2from productwhere p_code like '%/%';2 3• P_CODE PART2• -------- --------• 11QER/31 31• 13-Q2/P2 P2• 14-Q1/L3 L3• 2232/QTY QTY• 2232/QWE QWE• 2238/QPD QPD• WR3/TT3 TT3

• 7 rows selected.

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SQL> select p_code, substr(P_code, 1, instr(p_code,'/')-1) part1, substr(P_code, instr(p_code,'/')+1) part2from productwhere p_code like '%/%'; 2 3

• P_CODE PART1 PART2• -------- -------- --------• 11QER/31 11QER 31• 13-Q2/P2 13-Q2 P2• 14-Q1/L3 14-Q1 L3• 2232/QTY 2232 QTY• 2232/QWE 2232 QWE• 2238/QPD 2238 QPD• WR3/TT3 WR3 TT3

• 7 rows selected.

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Remove the period from price

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SQL> select (substr(P_price, 1, instr(p_price,'.')-1)|| substr (P_price, instr(p_price,'.')+1)) as pricefrom product; 2 3

• PRICE• --------------------------------------------------------------------------------• 10999• 1499• 1749• 3995• 4399• 10992• 9987• 3895• 995• 144• 499

• PRICE• --------------------------------------------------------------------------------• 25699• 587• 699• 845• 11995

• 16 rows selected.

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COMMON ERRORS

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INTEGRITY CONSTRAINT VIOLATION

SQL> select * from trial1;

SN SCITY--- --------------------111 baltimore

SQL> insert into trial2 values (234,222);insert into trial2 values (234,222)• *ERROR at line 1:ORA-02291: integrity constraint

(AGGARWAL.SYS_C0026818) violated - parent key not found

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TOO MANY VALUES

• SQL> l• 1 select * from invoice where cust_code in• 2* (select inv-num, inv_date from invoice)• SQL> /• (select inv-num, inv_date from invoice)• *• ERROR at line 2:• ORA-00913: too many values

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LEASE TABLE

• SQL> desc lease;• Name Null? Type• ----------------------------------------- --------

----------------------------• L_NO NOT NULL CHAR(6)• P_NO CHAR(5)• RENTER_NO CHAR(4)• RENT NUMBER(5)• PAYMENT CHAR(5)• START_DATE DATE• FIN_DATE DATE

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MISMATCH COMPARISON

SQL> /

• select * from lease where rent in (select payment from lease)

*

ERROR at line 1:

ORA-01722: invalid number

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UNIQUE CONSTRAINT VIOLATION

SQL> select * from trial1;SN SCITY--- --------------------111 baltimoreSQL> insert into trial1 values (111,'mass');insert into trial1 values*ERROR at line 1:ORA-00001: unique constraint

(AGGARWAL.SYS_C0026745) violated

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NOT a Single_Group Function

• select distinct l_no, sum(rent)

• *

• ERROR at line 1:

• ORA-00937: not a single-group group function