<s>
A	O
relational	B-Application
data	I-Application
stream	I-Application
management	I-Application
system	I-Application
(	O
RDSMS	O
)	O
is	O
a	O
distributed	O
,	O
in-memory	O
data	B-General_Concept
stream	I-General_Concept
management	I-General_Concept
system	I-General_Concept
(	O
DSMS	B-General_Concept
)	O
that	O
is	O
designed	O
to	O
use	O
standards-compliant	O
SQL	B-Language
queries	O
to	O
process	O
unstructured	O
and	O
structured	O
data	O
streams	O
in	O
real-time	O
.	O
</s>
<s>
Unlike	O
SQL	B-Language
queries	O
executed	O
in	O
a	O
traditional	O
RDBMS	O
,	O
which	O
return	O
a	O
result	O
and	O
exit	O
,	O
SQL	B-Language
queries	O
executed	O
in	O
a	O
RDSMS	O
do	O
not	O
exit	O
,	O
generating	O
results	O
continuously	O
as	O
new	O
data	O
become	O
available	O
.	O
</s>
<s>
Continuous	O
SQL	B-Language
queries	O
in	O
a	O
RDSMS	O
use	O
the	O
SQL	B-Language
Window	O
function	O
to	O
analyze	O
,	O
join	O
and	O
aggregate	O
data	O
streams	O
over	O
fixed	O
or	O
sliding	O
windows	O
.	O
</s>
<s>
Continuous	O
SQL	B-Language
queries	O
in	O
a	O
RDSMS	O
conform	O
to	O
the	O
ANSI	O
SQL	B-Language
standards	O
.	O
</s>
<s>
The	O
most	O
common	O
RDSMS	O
SQL	B-Language
query	O
is	O
performed	O
with	O
the	O
declarative	O
SELECT	O
statement	O
.	O
</s>
<s>
A	O
continuous	O
SQL	B-Language
SELECT	O
operates	O
on	O
data	O
across	O
one	O
or	O
more	O
data	O
streams	O
,	O
with	O
optional	O
keywords	O
and	O
clauses	O
that	O
include	O
FROM	O
with	O
an	O
optional	O
JOIN	O
subclause	O
to	O
specify	O
the	O
rules	O
for	O
joining	O
multiple	O
data	O
streams	O
,	O
the	O
WHERE	O
clause	O
and	O
comparison	O
predicate	O
to	O
restrict	O
the	O
records	O
returned	O
by	O
the	O
query	O
,	O
GROUP	O
BY	O
to	O
project	O
streams	O
with	O
common	O
values	O
into	O
a	O
smaller	O
set	O
,	O
HAVING	O
to	O
filter	O
records	O
resulting	O
from	O
a	O
GROUP	O
BY	O
,	O
and	O
ORDER	O
BY	O
to	O
sort	O
the	O
results	O
.	O
</s>
<s>
RDSMS	O
SQL	B-Language
queries	O
also	O
operate	O
on	O
data	O
streams	O
over	O
time	O
or	O
row-based	O
windows	O
.	O
</s>
<s>
The	O
following	O
example	O
shows	O
a	O
second	O
continuous	O
SQL	B-Language
query	O
using	O
the	O
WINDOW	O
clause	O
with	O
a	O
one-second	O
duration	O
.	O
</s>
