database design - Cassandra: Which schema for table-like mappings? -

i have tried different approaches can't find solution problem: data table-like, meaning have 1 data point (float) each combination of inputs set of strings:

(a mapping of s × s → ℝ ) 

i want model schema can following lookups:

• all pairs of strings value in range
• for given input string, strings mapped value in range
• for given combination of input strings mapped value

since mapping symmetrical (m(x,y) == m(y,x) ), great if had store the
n*(n+1) / 2 unique values instead of n^2 total mappings.

what have tried far:

1. s1+" "+s2 row key , value column name
2. s1 row key , composite key of [s2:value] column name
3. s1 row key, s2 column name, value column value.

but unfortunately, these approaches don't let me queries need. possible in cassandra?

cassandra not support first query --- all pairs of strings value in range --- since currently, cassandra allows range queries @ least 1 eq on where clause. however, second , third queries doable :)

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example

consider following example:

cqlsh:so> desc table string_mappings; create table string_mappings (   s1 ascii,   s2 ascii,   value float,   primary key (s1, s2, value) )  

and have following tuples:

cqlsh:so> select * string_mappings;   s1    | s2    | value -------+-------+-------  hello | hello |     1  hello | world |   0.2  stack | hello |     0  stack | stack |     1  stack | world |     0  world | world |     1 

your first query not work cassandra not support range queries without eq on where clause:

cqlsh:so> select * string_mappings value>0.5; bad request: primary key part value cannot restricted (preceding part s2 either not restricted or non-eq relation) 

however, following range query (your second query) fine since has eq:

cqlsh:so> select * string_mappings value > 0.5 , s2='hello' allow filtering;   s1    | s2    | value -------+-------+-------  hello | hello |     1 

and remember put allow filtering keyword, or following error:

cqlsh:so> select * string_mappings value > 0.5 , s2='hello'; bad request: cannot execute query might involve data filtering , may have unpredictable performance. if want execute query despite performance unpredictability, use allow filtering 

finally, third query not problem :)

cqlsh:so> select * string_mappings s1='hello' , s2='world';   s1    | s2    | value -------+-------+-------  hello | world |   0.2