Throw an error when an invalid expression is used with aux iterators

The following query was fixed previously:

    SELECT 'value' FROM cpu

This ended up hitting the `buildExprIterator()` code path and was
handled properly. But this query:

    SELECT 'value', value FROM cpu

This took a different code path that would trigger a panic because it
triggered a panic instead of an error condition. This code path has now
been modified to trigger an error instead of a panic.

Fixes #6248.

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Bugfixes
 
 - [#6206](https://github.com/influxdata/influxdb/issues/6206): Handle nil values from the tsm1 cursor correctly.
+- [#6248](https://github.com/influxdata/influxdb/issues/6248): Panic using incorrectly quoted "queries" field key.
 
 ## v0.12.0 [2016-04-05]
 ### Release Notes

influxql/select.go

@@ -110,20 +110,27 @@ func buildAuxIterators(fields Fields, ic IteratorCreator, opt IteratorOptions) (
 
 	// Generate iterators for each field.
 	itrs := make([]Iterator, len(fields))
-	for i, f := range fields {
-		expr := Reduce(f.Expr, nil)
-		switch expr := expr.(type) {
-		case *VarRef:
-			itrs[i] = aitr.Iterator(expr.Val)
-		case *BinaryExpr:
-			itr, err := buildExprIterator(expr, aitr, opt)
-			if err != nil {
-				return nil, fmt.Errorf("error constructing iterator for field '%s': %s", f.String(), err)
+	if err := func() error {
+		for i, f := range fields {
+			expr := Reduce(f.Expr, nil)
+			switch expr := expr.(type) {
+			case *VarRef:
+				itrs[i] = aitr.Iterator(expr.Val)
+			case *BinaryExpr:
+				itr, err := buildExprIterator(expr, aitr, opt)
+				if err != nil {
+					return fmt.Errorf("error constructing iterator for field '%s': %s", f.String(), err)
+				}
+				itrs[i] = itr
+			default:
+				return fmt.Errorf("invalid expression type: %T", expr)
 			}
-			itrs[i] = itr
-		default:
-			panic("unreachable")
 		}
+		return nil
+	}(); err != nil {
+		Iterators(Iterators(itrs).filterNonNil()).Close()
+		aitr.Close()
+		return nil, err
 	}
 
 	// Background the primary iterator since there is no reader for it.

influxql/select_test.go

@@ -2021,6 +2021,10 @@ func TestSelect_InvalidQueries(t *testing.T) {
 			q:   `SELECT 'value' FROM cpu`,
 			err: `invalid expression type: *influxql.StringLiteral`,
 		},
+		{
+			q:   `SELECT 'value', value FROM cpu`,
+			err: `invalid expression type: *influxql.StringLiteral`,
+		},
 	}
 
 	for i, tt := range tests {