Examples with Equality org.apache.druid.segment.join.Equality used on opensource projects

Example 1 with Equality

use of org.apache.druid.segment.join.Equality in project druid by druid-io.

the class JoinFilterCorrelations method findCorrelatedBaseTableColumns.

/**
 * For each rhs column that appears in the equiconditions for a table's JoinableClause,
 * we try to determine what base table columns are related to the rhs column through the total set of equiconditions.
 * We do this by searching backwards through the chain of join equiconditions using the provided equicondition map.
 * <p>
 * For example, suppose we have 3 tables, A,B,C, joined with the following conditions, where A is the base table:
 * A.joinColumn == B.joinColumn
 * B.joinColum == C.joinColumnenableRewriteValueColumnFilters
 * <p>
 * We would determine that C.joinColumn is correlated with A.joinColumn: we first see that
 * C.joinColumn is linked to B.joinColumn which in turn is linked to A.joinColumn
 * <p>
 * Suppose we had the following join conditions instead:
 * f(A.joinColumn) == B.joinColumn
 * B.joinColum == C.joinColumn
 * In this case, the JoinFilterColumnCorrelationAnalysis for C.joinColumn would be linked to f(A.joinColumn).
 * <p>
 * Suppose we had the following join conditions instead:
 * A.joinColumn == B.joinColumn
 * f(B.joinColum) == C.joinColumn
 * <p>
 * Because we cannot reverse the function f() applied to the second table B in all cases,
 * we cannot relate C.joinColumn to A.joinColumn, and we would not generate a correlation for C.joinColumn
 *
 * @param joinableClauses     List of joinable clauses for the query
 * @param tablePrefix         Prefix for a join table
 * @param rhsRewriteCandidate RHS rewrite candidate that we find correlated base table columns for
 * @param equiConditions      Map of equiconditions, keyed by the right hand columns
 * @return A list of correlatation analyses for the equicondition RHS columns that reside in the table associated with
 * the tablePrefix
 */
private static Optional<Map<String, JoinFilterColumnCorrelationAnalysis>> findCorrelatedBaseTableColumns(JoinableClauses joinableClauses, String tablePrefix, RhsRewriteCandidate rhsRewriteCandidate, Equiconditions equiConditions) {
    JoinableClause clauseForTablePrefix = rhsRewriteCandidate.getJoinableClause();
    JoinConditionAnalysis jca = clauseForTablePrefix.getCondition();
    Set<String> rhsColumns = new HashSet<>();
    if (rhsRewriteCandidate.isDirectRewrite()) {
        // If we filter on a RHS join column, we only need to consider that column from the RHS side
        rhsColumns.add(rhsRewriteCandidate.getRhsColumn());
    } else {
        for (Equality eq : jca.getEquiConditions()) {
            rhsColumns.add(tablePrefix + eq.getRightColumn());
        }
    }
    Map<String, JoinFilterColumnCorrelationAnalysis> correlations = new LinkedHashMap<>();
    for (String rhsColumn : rhsColumns) {
        Set<String> correlatedBaseColumns = new HashSet<>();
        Set<Expr> correlatedBaseExpressions = new HashSet<>();
        getCorrelationForRHSColumn(joinableClauses, equiConditions, rhsColumn, correlatedBaseColumns, correlatedBaseExpressions);
        if (correlatedBaseColumns.isEmpty() && correlatedBaseExpressions.isEmpty()) {
            continue;
        }
        correlations.put(rhsColumn, new JoinFilterColumnCorrelationAnalysis(rhsColumn, correlatedBaseColumns, correlatedBaseExpressions));
    }
    if (correlations.size() == 0) {
        return Optional.empty();
    } else {
        return Optional.of(correlations);
    }
}