RA3 implements type safe queries on large tabular datasets.

• Partitioned joins and groupings.
• Inner, left, right and full outer joins.
• Projections and filters.
• Selection of top K elements
• Data import and export to and from csv.
• Streaming data import and export via fs2 streams.
• RA3 supports only integer, long, double, string and instant (datetime) data types.

The following table level operators are available in ra3:

• simple query, i.e. element-wise filter and projection. Corresponds to SQL queries of SELECT and WHERE.
• count query, i.e. element-wise filter and count. Corresponds to SQL queries of SELECT count(*) and WHERE (but no GROUP BY).
• equi-join, i.e. join with a join condition restricted to be equality among two columns.
• group by then reduce. Corresponds to SELECT aggregations, WHERE, GROUP BY clauses of SQL
• group by then count. Corresponds to SELECT count(*), WHERE, GROUP BY clauses of SQL
• approximate selection of the top K number of elements by a single column

Common features of SQL engines which are not available:

• arbitrary join condition (e.g. join by inequalities)
• complete products of tables (Cartesian products)
• full table sort
• sub-query in filter (WHERE in (select id FROM ..)). This can be rewritten into a join.
• queries are not heuristically reorganized (optimized)

RA3 supports Scala 3 only because it uses the following language features not present in Scala2:

• Recursive encoding of tuples
• match types and dependent typing
• inline and transparent inline methods

For user facing documentation see the scaladoc of the ra3 package.

See an exampe in the example/ folder.

• direct literal or column comparison with a missing value always returns false (like Double.NaN)
• filter for missing values is possible with explicit isMissing (like sql is null)
• joins do not join on missing values i.e.:
• • inner join does not return missing values in the join column
• • outer join returns one row for each missing value row, with nothing joined from other tables (ie all missing)
• group by on missing treats missing as an other (single) group
• count distinct in groups do not count missing values
• min/max in groups do not count missing values
• all elementwise operations, including predicates propagate missing value i.e. if either of their input is missing the result is missing, except for the isMissing oeprator
• logic operators follow 3 values logic (https://en.wikipedia.org/wiki/Three-valued_logic#Kleene_and_Priest_logics)
• printf etc formats missing into a non missing string
• Missing values are encoded as one of the values of the data type. As such these values can not be used for to encode their usual non-missing semantics: Double.NaN, Long.MinValue, Int.MinValue, "\u0001".
• ordering of missing values below or above other elements are unobservable in ra3 because there is no full table sort operation. The operation which selects the top-k elements will not return missing values.

example_cli/ is a self contained example built with scala-cli. Open in a separate vscode workspace.

sbt test

licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT warranties OR CONDITIONS OF ANY KIND, either express or implied. See the license for the specific language governing permissions and limitations under the License.