entc/gen: reduce the usage of DISTINCT in queries (#3305)

Most queries are not graph traversals but rather regular table scans,
in which case the DISTINCT clause is not needed as duplicates cannot be
returned (unless query was modified by the user).

dialect/sql/sqlgraph/graph.go

@@ -577,6 +577,17 @@ type QuerySpec struct {
 	Assign     func(columns []string, values []any) error
 }
 
+// NewQuerySpec creates a new node query spec.
+func NewQuerySpec(table string, columns []string, id *FieldSpec) *QuerySpec {
+	return &QuerySpec{
+		Node: &NodeSpec{
+			ID:      id,
+			Table:   table,
+			Columns: columns,
+		},
+	}
+}
+
 // QueryNodes queries the nodes in the graph query and scans them to the given values.
 func QueryNodes(ctx context.Context, drv dialect.Driver, spec *QuerySpec) error {
 	builder := sql.Dialect(drv.Dialect())

entc/gen/template/dialect/sql/query.tmpl

@@ -262,22 +262,13 @@ func ({{ $receiver }} *{{ $builder }}) sqlCount(ctx context.Context) (int, error
 }
 
 func ({{ $receiver }} *{{ $builder }}) querySpec() *sqlgraph.QuerySpec {
-	_spec := &sqlgraph.QuerySpec{
-		Node: &sqlgraph.NodeSpec{
-			Table: {{ $.Package }}.Table,
-			Columns: {{ $.Package }}.Columns,
-			{{- if $.HasOneFieldID }}
-				ID: &sqlgraph.FieldSpec{
-					Type: field.{{ $.ID.Type.ConstName }},
-					Column: {{ $.Package }}.{{ $.ID.Constant }},
-				},
-			{{- end }}
-		},
-		From: {{ $receiver }}.sql,
-		Unique: true,
-	}
+	_spec := sqlgraph.NewQuerySpec({{ $.Package }}.Table, {{ $.Package }}.Columns, {{ if $.HasOneFieldID }}sqlgraph.NewFieldSpec({{ $.Package }}.{{ $.ID.Constant }}, field.{{ $.ID.Type.ConstName }}){{ else }}nil{{ end }})
+	{{- /* Setup any intermediate queries if exist (traversal path). */}}
+	_spec.From = {{ $receiver }}.sql
 	if unique := {{ $receiver }}.ctx.Unique; unique != nil {
 		_spec.Unique = *unique
+	} else if {{ $receiver }}.path != nil {
+		_spec.Unique = true
 	}
 	if fields := {{ $receiver }}.ctx.Fields; len(fields) > 0 {
 		_spec.Node.Columns = make([]string, 0, len(fields))