<s>
A	O
table	B-Application
is	O
a	O
collection	O
of	O
related	O
data	O
held	O
in	O
a	O
table	B-Application
format	O
within	O
a	O
database	O
.	O
</s>
<s>
It	O
consists	O
of	O
columns	B-Application
and	O
rows	B-Application
.	O
</s>
<s>
In	O
relational	B-Application
databases	I-Application
,	O
and	O
flat	B-Application
file	I-Application
databases	I-Application
,	O
a	O
table	B-Application
is	O
a	O
set	O
of	O
data	O
elements	O
(	O
values	O
)	O
using	O
a	O
model	O
of	O
vertical	O
columns	B-Application
(	O
identifiable	O
by	O
name	O
)	O
and	O
horizontal	O
rows	B-Application
,	O
the	O
cell	O
being	O
the	O
unit	O
where	O
a	O
row	O
and	O
column	O
intersect	O
.	O
</s>
<s>
A	O
table	B-Application
has	O
a	O
specified	O
number	O
of	O
columns	B-Application
,	O
but	O
can	O
have	O
any	O
number	O
of	O
rows	B-Application
.	O
</s>
<s>
A	O
specific	O
choice	O
of	O
columns	B-Application
which	O
uniquely	O
identify	O
rows	B-Application
is	O
called	O
the	O
primary	B-Application
key	I-Application
.	O
</s>
<s>
"	O
Table	B-Application
"	O
is	O
another	O
term	O
for	O
"	B-Language
relation	I-Language
"	I-Language
;	O
although	O
there	O
is	O
the	O
difference	O
in	O
that	O
a	O
table	B-Application
is	O
usually	O
a	O
multiset	B-Language
(	O
bag	O
)	O
of	O
rows	B-Application
where	O
a	O
relation	B-Language
is	O
a	O
set	O
and	O
does	O
not	O
allow	O
duplicates	O
.	O
</s>
<s>
Besides	O
the	O
actual	O
data	O
rows	B-Application
,	O
tables	O
generally	O
have	O
associated	O
with	O
them	O
some	O
metadata	O
,	O
such	O
as	O
constraints	B-Language
on	O
the	O
table	B-Application
or	O
on	O
the	O
values	O
within	O
particular	O
columns	B-Application
.	O
</s>
<s>
The	O
data	O
in	O
a	O
table	B-Application
does	O
not	O
have	O
to	O
be	O
physically	O
stored	O
in	O
the	O
database	O
.	O
</s>
<s>
Views	B-Language
also	O
function	O
as	O
relational	O
tables	O
,	O
but	O
their	O
data	O
are	O
calculated	O
at	O
query	O
time	O
.	O
</s>
<s>
or	O
Oracle	B-General_Concept
,	O
</s>
<s>
for	O
example	O
)	O
can	O
also	O
be	O
thought	O
of	O
as	O
views	B-Language
.	O
</s>
<s>
In	O
many	O
systems	O
for	O
computational	O
statistics	O
,	O
such	O
as	O
R	B-Language
and	O
Python	B-Language
's	O
pandas	B-Application
,	O
a	O
data	O
frame	O
or	O
data	B-Application
table	I-Application
is	O
a	O
data	O
type	O
supporting	O
the	O
table	B-Application
abstraction	O
.	O
</s>
<s>
Conceptually	O
,	O
it	O
is	O
a	O
list	O
of	O
records	O
or	O
observations	O
all	O
containing	O
the	O
same	O
fields	O
or	O
columns	B-Application
.	O
</s>
<s>
The	O
implementation	O
consists	O
of	O
a	O
list	O
of	O
arrays	B-Data_Structure
or	I-Data_Structure
vectors	I-Data_Structure
,	O
each	O
with	O
a	O
name	O
.	O
</s>
<s>
In	O
terms	O
of	O
the	O
relational	B-Architecture
model	I-Architecture
of	O
databases	O
,	O
a	O
table	B-Application
can	O
be	O
considered	O
a	O
convenient	O
representation	O
of	O
a	O
relation	B-Language
,	O
but	O
the	O
two	O
are	O
not	O
strictly	O
equivalent	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
SQL	B-Application
table	I-Application
can	O
potentially	O
contain	O
duplicate	O
rows	B-Application
,	O
whereas	O
a	O
true	O
relation	B-Language
cannot	O
contain	O
duplicate	O
rows	B-Application
that	O
we	O
call	O
tuples	B-Application
.	O
</s>
<s>
Similarly	O
,	O
representation	O
as	O
a	O
table	B-Application
implies	O
a	O
particular	O
ordering	O
to	O
the	O
rows	B-Application
and	O
columns	B-Application
,	O
whereas	O
a	O
relation	B-Language
is	O
explicitly	O
unordered	O
.	O
</s>
<s>
However	O
,	O
the	O
database	O
system	O
does	O
not	O
guarantee	O
any	O
ordering	O
of	O
the	O
rows	B-Application
unless	O
an	O
ORDER	B-Language
BY	I-Language
clause	O
is	O
specified	O
in	O
the	O
SELECT	O
statement	O
that	O
queries	O
the	O
table	B-Application
.	O
</s>
<s>
An	O
equally	O
valid	O
representation	O
of	O
a	O
relation	B-Language
is	O
as	O
an	O
n-dimensional	O
chart	O
,	O
where	O
n	O
is	O
the	O
number	O
of	O
attributes	O
(	O
a	O
table	B-Application
's	O
columns	B-Application
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
relation	B-Language
with	O
two	O
attributes	O
and	O
three	O
values	O
can	O
be	O
represented	O
as	O
a	O
table	B-Application
with	O
two	O
columns	B-Application
and	O
three	O
rows	B-Application
,	O
or	O
as	O
a	O
two-dimensional	O
graph	O
with	O
three	O
points	O
.	O
</s>
<s>
The	O
table	B-Application
and	O
graph	O
representations	O
are	O
only	O
equivalent	O
if	O
the	O
ordering	O
of	O
rows	B-Application
is	O
not	O
significant	O
,	O
and	O
the	O
table	B-Application
has	O
no	O
duplicate	O
rows	B-Application
.	O
</s>
<s>
In	O
non-relational	O
systems	O
,	O
hierarchical	B-General_Concept
databases	I-General_Concept
,	O
the	O
distant	O
counterpart	O
of	O
a	O
table	B-Application
is	O
a	O
structured	O
file	B-Operating_System
,	O
representing	O
the	O
rows	B-Application
of	O
a	O
table	B-Application
in	O
each	O
row	O
of	O
the	O
file	B-Operating_System
and	O
each	O
column	O
in	O
a	O
row	O
.	O
</s>
<s>
Unlike	O
a	O
spreadsheet	B-Application
,	O
the	O
datatype	O
of	O
a	O
column	O
is	O
ordinarily	O
defined	O
by	O
the	O
schema	B-Application
describing	O
the	O
table	B-Application
.	O
</s>
<s>
Some	O
SQL	B-Language
systems	O
,	O
such	O
as	O
SQLite	B-Language
,	O
are	O
less	O
strict	O
about	O
column	O
datatype	O
definitions	O
.	O
</s>
