jy4618272 / scala_sql Goto Github PK

##Motivation In some scenario of stream computation, the raw data are usually collected from a message queue like kafka，which will be persistented for further analyze. For most of the time, the raw data are store as a simple java bean in memory and could easily be converted to a Map. The scala_sql is designed to run simple SQL on the data structure List<Map>, allowing the programmer to do some real time computing.

###Demo suppose there is a List called user,which contains these data:
[name:tsc,age:30,sex:male]
[name:syy,age:29,sex:female]
[name:dudu,age:1,sex:male]
[name:xiaohua,age:2,sex:null]
[name:tsc,age:19,sex:male]
[name:tsc,age:99,sex:female]
[name:tsc,age:30,sex:female]

then

Engine.query(user,"select count(user) as number,name from user group by name")

will result in：
[number:1,name:dudu]
[number:4,name:tsc]
[number:1,name:xiaohua]
[number:1,name:syy]

###supported function and clause max,min,sum,count,count(distinct),avg order by, group by, limit

###supported java/scala data type String,Integer,Double,Date

###need to improve 1.currently the java/scala data type are implicitly converted to the build-in type using the scala implicit class, however it can't not convert null which is a special type in java, so when doing computation like sum,order by on column which has a null value, the code will throw an exception. In another word, if a column has a null value, you can not do computation on it.

2.The engine uses the build in function

sortBy[B](f: A => B)(implicit ord: Ordering[B]): Repr = sorted(ord on f)

to do order by, as the engine do not support clause like

order by a desc, b asc