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DB2TRANSPARENCIES

(Unit 7)

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11 The JOIN Operation

Objectives - Student will

Understand how to code an efficient JOIN

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11 The JOIN Operation

Matches one table to another based on data

common between the tables

Join Predicate

Columns with identical characteristics

Result Table contains rows comprised of columns from

all the tables in the join

There is NO JOIN VERB

May join up to 15 tables

May join a table to itself (reflexive)

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11 The JOIN Operation

Example 50

select *

from orders

, items

where p_no = 102;

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11 The JOIN Operation

Example 51

select c.company

, o.o_no

, o.o_date

from customer c

, orders o

where c.c_no = o.c_no;

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11 The JOIN Operation

Example 52

select e.fname || ' ' || e.lname

, o.o_no , o.o_date , i.p_no , i.quantity

, i.quantity * i.price

from orders o , items i , employee e

where o.o_no = i.o_no and o.s_no = e.e_no

order by 1, 2;

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11 the JOIN Operation

Example 53

select b.fname || ' ' || b.lname

, b.department

from staff a

, staff b

where b.department = a.department

and a.empid = 110;

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11 The JOIN Operation

Using Composite Keys (Compound Key)

Will have multiple conditions within the WHERE clause, one

for each column of the key

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12 UNION

Objectives - Student will

Understand how to code a UNION

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12 UNION

Merge the results of two or more queries

Removes duplicate rows

Each SELECT must contain the same number of

expressions (columns)

Corresponding expressions must be the comparabledata types

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12 UNION

Example 54

select 'Part ', pno, 'Made in England

'

from part

where city = 'london'

UNION

select 'Supplier', sno, 'Located in

England'

from supplier

where city = 'london'

order by 2 desc;

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12 UNION

UNION ALL

Includes all rows returned (does not eliminate duplicates)

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12 UNION

Example 55/56

select 'Part ', pno

from part

where city = 'london'

UNION ALL

select Part , pno

from partsupp

order by 1;

select 'Part ', pno

from part

where city = 'london'

UNION

select Part , pno

from partsupp

order by 1;