如何應用cassandra中每個唯一組合列值的限制？

Question

我有一個樣本表結構是這樣的：

CREATE TABLE testcomposite ( day text, name text, lpt varint, details text, PRIMARY KEY (day, name, lpt) )

，我有這樣的數據：

cqlsh:KS> select * from testcomposite;

day | name | lpt | details ------+---------+---------+-------- day1 | name1 | 10 | abcdef day1 | name1 | 11 | abcdef day1 | name1 | 21 | abcdef day1 | name2 | 10 | abcdef day1 | name2 | 11 | abcdef

是否可以查詢得到像這樣的結果，其中每行包含唯一的name字段，其​​最大值爲lpt值？

day | name | lpt | details ------+---------+---------+-------- day1 | name1 | 21 | abcdef day1 | name2 | 11 | abcdef

Answer 1

CREATE FUNCTION state_group_and_max(state map<text, int>, type text, amount int) 
    CALLED ON NULL INPUT 
    RETURNS map<text, int> 
    LANGUAGE java AS ' 
    Integer count = (Integer) state.get(type); if (count == null) count = amount; else count = Math.max(count, amount); state.put(type, count); return state; ' ; 


    CREATE OR REPLACE AGGREGATE group_and_max(text, int) 
    SFUNC state_group_and_max 
    STYPE map<text, int> 
    INITCOND {}; 

cqlsh:test> select group_and_max(name,lpt) from testcomposite where day = 'day1'; 

test.group_and_max(name, lpt) 
------------------------------- 
    {'name1': 21, 'name2': 11}