Don't optimize comparison query for druid mvd (#5536)

runtime/metricsview/ast.go

@@ -62,9 +62,10 @@ type SelectNode struct {
 // The Name must always match a the name of a dimension/measure in the metrics view or a computed field specified in the request.
 // This means that if two columns in different places in the AST have the same Name, they're guaranteed to resolve to the same value.
 type FieldNode struct {
-	Name  string
-	Label string
-	Expr  string
+	Name       string
+	Label      string
+	Expr       string
+	AutoUnnest bool
 }
 
 // ExprNode represents an expression for a WHERE clause.
@@ -154,7 +155,9 @@ func NewAST(mv *runtimev1.MetricsViewSpec, sec *runtime.ResolvedSecurity, qry *Q
 				return nil, fmt.Errorf("failed to unnest field %q: %w", f.Name, err)
 			}
 
-			if !auto {
+			if auto {
+				f.AutoUnnest = true
+			} else {
 				ast.unnests = append(ast.unnests, tblWithAlias)
 				f.Expr = ast.sqlForMember(unnestAlias, f.Name)
 			}

runtime/metricsview/executor_rewrite_approx_comparisons.go

@@ -48,10 +48,14 @@ func (e *Executor) rewriteApproxComparisonNode(a *AST, n *SelectNode) bool {
 	}
 	sortField := a.Root.OrderBy[0]
 
-	// if there are unnests in the query, we can't rewrite the query for Druid
-	// it fails with join on cte having multi value dimension, issue - https://github.com/apache/druid/issues/16896
-	if e.olap.Dialect() == drivers.DialectDruid && len(a.unnests) > 0 {
-		return false
+	if e.olap.Dialect() == drivers.DialectDruid {
+		// if there are unnests in the query, we can't rewrite the query for Druid
+		// it fails with join on cte having multi value dimension, issue - https://github.com/apache/druid/issues/16896
+		for _, dim := range n.FromSelect.DimFields {
+			if dim.AutoUnnest {
+				return false
+			}
+		}
 	}
 
 	// Find out what we're sorting by