kdb+和一般数据库还是很多不同

〇〇

//fby函数触发了1个bug
q)t2: ([] name:();sal:())
q)t2
name sal
--------
q)`t2 insert (`wang`li`zhao; 12 14 10)
0 1 2
q)t2
name sal
--------
wang 12
li   14
zhao 10
q)select from t2 where sal=(avg;sal)
'length
=
12 14 10
(avg;12 14 10)
q)select from t2 where sal=(avg;sal)  fby 1
k){@[(#y)#x[0]0#x 1;g;:;x[0]'x[1]g:.=y]}
'type
=:
1
q.q))select from t2 where sal=(avg sal)
't2
q.q))
q.q))t2
't2
q.q))t1
't1
q.q))\\

〇〇

//用文档中的例子
q)\l sp.q
+`p`city!(`p$`p1`p2`p3`p4`p5`p6`p1`p2;`london`london`london`london`london`lon..
(`s#+(,`color)!,`s#`blue`green`red)!+(,`qty)!,900 1000 1200
+`s`p`qty!(`s$`s1`s1`s1`s2`s3`s4;`p$`p1`p4`p6`p2`p2`p4;300 200 100 400 200 300)
q)sp
s  p  qty
---------
s1 p1 300
s1 p2 200
s1 p3 400
s1 p4 200
s4 p5 100
s1 p6 100
s2 p1 300
s2 p2 400
s3 p2 200
s4 p2 200
s4 p4 300
s1 p5 400
q)select p1,avg qty by p from sp
'p1
q)select p,avg qty by p from sp
p | p               qty
--| -------------------
p1| `p$`p1`p1       300
p2| `p$`p2`p2`p2`p2 250
p3| `p$,`p3         400
p4| `p$`p4`p4       250
p5| `p$`p5`p5       250
p6| `p$,`p6         100
q)select from sp where qty>(avg;qty) fby p
s  p  qty
---------
s2 p2 400
s4 p4 300
s1 p5 400

〇〇

//上述不写多余的p,就是常见的结果
q)select avg qty by p from sp
p | qty
--| ---
p1| 300
p2| 250
p3| 400
p4| 250
p5| 250
p6| 100