SORT AGGREGATE

SORT AGGREGATE做为sort的option之一比较特殊，他并不做sort

SORT AGGREGATE作用于所有的data set上，用于aggregate function，例如sum, count, avg, min, max

SQL>
select max(x)
from test;





Execution
Plan

----------------------------------------------------------

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=3 Card=1 Bytes=5)

1
0 SORT
(AGGREGATE)

2
1 INDEX
(FULL
SCAN (MIN/MAX))
OF 'TEST_IDX'
(NON-UNIQUE)
(

Cost=3
Card=7140
Bytes=35700)



Statistics

----------------------------------------------------------

0 recursive calls

0
db block
gets

2
consistent gets

0
physical reads

0
redo size

491
bytes sent
via SQL*Net
to client

650
bytes received
via SQL*Net
from client

2
SQL*Net
roundtrips
to/from
client

0
sorts (memory) -- no sort here

0
sorts (disk)

1
rows processed

如果aggregate function不是作用于与所有的data set上，还是作用于不同的group上，那么操作类型将会变为SORT (GROUP BY)，这时会有sort发生

SQL>
select x,count(*)
from test
group by
x;



7138 rows
selected.





Execution
Plan

----------------------------------------------------------

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=20 Card=7137 Bytes=3

5685)



1
0 SORT
(GROUP
BY)
(Cost=20
Card=7137
Bytes=35685)

2
1 TABLE
ACCESS (FULL)
OF 'TEST'
(Cost=3
Card=7140
Bytes=35

700)



Statistics

----------------------------------------------------------

0 recursive calls

0
db block
gets

19
consistent gets

0
physical reads

0
redo size

151790
bytes sent
via SQL*Net
to client

5875
bytes received
via SQL*Net
from client

477
SQL*Net
roundtrips
to/from
client

1
sorts (memory)

0
sorts (disk)

7138
rows processed