dialect/sql: add Selector.HasJoins helper (#3418)

dialect/sql/builder.go

@@ -2025,6 +2025,9 @@ func Distinct(idents ...string) string {
 // TableView is a view that returns a table view. Can be a Table, Selector or a View (WITH statement).
 type TableView interface {
 	view()
+	// C returns a formatted string prefixed
+	// with the table view qualifier.
+	C(string) string
 }
 
 // queryView allows using Querier (expressions) in the FROM clause.
@@ -2032,6 +2035,13 @@ type queryView struct{ Querier }
 
 func (*queryView) view() {}
 
+func (q *queryView) C(column string) string {
+	if tv, ok := q.Querier.(TableView); ok {
+		return tv.C(column)
+	}
+	return column
+}
+
 // SelectTable is a table selector.
 type SelectTable struct {
 	Builder
@@ -2407,6 +2417,11 @@ func (s *Selector) TableName() string {
 	}
 }
 
+// HasJoins reports if the selector has any JOINs.
+func (s *Selector) HasJoins() bool {
+	return len(s.joins) > 0
+}
+
 // Join appends a `JOIN` clause to the statement.
 func (s *Selector) Join(t TableView) *Selector {
 	return s.join("JOIN", t)
@@ -3090,7 +3105,7 @@ func RowNumber() *WindowBuilder {
 }
 
 // Window returns a new window clause with a custom selector allowing
-// for custom windown functions.
+// for custom window functions.
 //
 //	Window(func(b *Builder) {
 //		b.WriteString(Sum(posts.C("duration")))

dialect/sql/builder_test.go

@@ -2371,3 +2371,10 @@ func TestFormattedColumnFromSubQuery(t *testing.T) {
 	}), "score").From(Table("table_name").As("table_name_alias")))
 	require.Equal(t, "`table_name_alias`.`score`", q.C("score"))
 }
+
+func TestSelector_HasJoins(t *testing.T) {
+	s := Select("*").From(Table("t1"))
+	require.False(t, s.HasJoins())
+	s.Join(Table("t2"))
+	require.True(t, s.HasJoins())
+}