func NewQueryEngine(next Processor, query *parser.SelectQuery, shards []uint32) (Processor, error) {
limit := query.Limit
var engine Processor = NewPassthroughEngineWithLimit(next, 1, limit)
var err error
if query.HasAggregates() {
engine, err = NewAggregatorEngine(query, engine)
} else if query.ContainsArithmeticOperators() {
engine, err = NewArithmeticEngine(query, engine)
}
fromClause := query.GetFromClause()
switch fromClause.Type {
case parser.FromClauseInnerJoin:
engine = NewJoinEngine(shards, query, engine)
case parser.FromClauseMerge:
tables := make([]string, len(fromClause.Names))
for i, name := range fromClause.Names {
tables[i] = name.Name.Name
}
engine = NewMergeEngine(shards, query.Ascending, engine)
case parser.FromClauseMergeRegex:
// At this point the regex should be expanded to the list of
// tables that will be queries
panic("QueryEngine cannot be called with merge function")
}
if err != nil {
return nil, err
}
return engine, nil
}
