<s>
A	O
GROUP	B-Language
BY	I-Language
statement	O
in	O
SQL	B-Language
specifies	O
that	O
a	O
SQL	B-Language
SELECT	I-Language
statement	O
partitions	O
result	O
rows	O
into	O
groups	O
,	O
based	O
on	O
their	O
values	O
in	O
one	O
or	O
several	O
columns	O
.	O
</s>
<s>
The	O
result	O
of	O
a	O
query	O
using	O
a	O
GROUP	B-Language
BY	I-Language
statement	O
contains	O
one	O
row	O
for	O
each	O
group	O
.	O
</s>
<s>
This	O
implies	O
constraints	O
on	O
the	O
columns	O
that	O
can	O
appear	O
in	O
the	O
associated	O
SELECT	B-Language
clause	O
.	O
</s>
<s>
As	O
a	O
general	O
rule	O
,	O
the	O
SELECT	B-Language
clause	O
may	O
only	O
contain	O
columns	O
with	O
a	O
unique	O
value	O
per	O
group	O
.	O
</s>
<s>
This	O
includes	O
columns	O
that	O
appear	O
in	O
the	O
GROUP	B-Language
BY	I-Language
clause	O
as	O
well	O
as	O
aggregates	O
resulting	O
in	O
one	O
value	O
per	O
group	O
.	O
</s>
<s>
Returns	O
the	O
data	O
of	O
the	O
example	O
pivot	B-Application
table	I-Application
which	O
answers	O
the	O
question	O
"	O
How	O
many	O
Units	O
did	O
we	O
sell	O
in	O
each	O
Region	O
for	O
every	O
Ship	O
Date	O
?	O
</s>
