treat Percentile as an error if we can't use PQL Percentile

If we can't successfully generate a PQL Percentile call, error
out rather than implementing an actual Percentile function in SQL.
This can be revisited if anyone needs it.

sql3/planner/expression.go

@@ -2899,7 +2899,7 @@ func (p *ExecutionPlanner) compileCallExpr(expr *parser.Call) (_ types.PlanExpre
 		return agg, nil
 
 	case "PERCENTILE":
-		agg := newPercentilePlanExpression(args[0], args[1], expr.ResultDataType)
+		agg := newPercentilePlanExpression(expr.Name.NamePos, args[0], args[1], expr.ResultDataType)
 		return agg, nil
 
 	case "CORR":

sql3/planner/expressionagg.go

@@ -881,15 +881,17 @@ func (n *maxPlanExpression) WithChildren(children ...types.PlanExpression) (type
 
 // percentilePlanExpression handles PERCENTILE()
 type percentilePlanExpression struct {
+	pos            parser.Pos
 	arg            types.PlanExpression
 	nthArg         types.PlanExpression
 	returnDataType parser.ExprDataType
 }
 
 var _ types.Aggregable = (*percentilePlanExpression)(nil)
 
-func newPercentilePlanExpression(arg types.PlanExpression, nthArg types.PlanExpression, returnDataType parser.ExprDataType) *percentilePlanExpression {
+func newPercentilePlanExpression(pos parser.Pos, arg types.PlanExpression, nthArg types.PlanExpression, returnDataType parser.ExprDataType) *percentilePlanExpression {
 	return &percentilePlanExpression{
+		pos:            pos,
 		arg:            arg,
 		nthArg:         nthArg,
 		returnDataType: returnDataType,
@@ -905,7 +907,7 @@ func (n *percentilePlanExpression) Evaluate(currentRow []interface{}) (interface
 }
 
 func (n *percentilePlanExpression) NewBuffer() (types.AggregationBuffer, error) {
-	return NewAggCountBuffer(n), nil
+	return nil, sql3.NewErrUnsupported(n.pos.Line, n.pos.Column, true, "Percentile call that can't be pushed down to PQL")
 }
 
 func (n *percentilePlanExpression) FirstChildExpr() types.PlanExpression {
@@ -941,7 +943,7 @@ func (n *percentilePlanExpression) WithChildren(children ...types.PlanExpression
 	if len(children) != 2 {
 		return nil, sql3.NewErrInternalf("unexpected number of children '%d'", len(children))
 	}
-	return newPercentilePlanExpression(children[0], children[1], n.returnDataType), nil
+	return newPercentilePlanExpression(n.pos, children[0], children[1], n.returnDataType), nil
 }
 
 // aggregator for CORR()

sql3/test/defs/defs_aggregate.go

@@ -494,6 +494,12 @@ var percentileTests = TableTest{
 			),
 			ExpErr: "integer, decimal or timestamp expression expected",
 		},
+		{
+			SQLs: sqls(
+				"SELECT percentile(i1, 50) AS avg_rows FROM percentile_test WHERE s1 != 'a'",
+			),
+			ExpErr: "Percentile call that can't be pushed down to PQL is not supported",
+		},
 		{
 			SQLs: sqls(
 				"SELECT percentile(i1, 50) AS p_rows FROM percentile_test",