sql: fix how nulls are sent to clients (#783)

sql: fix how nulls are sent to clients

_integration/go/mysql_test.go

@@ -74,7 +74,7 @@ func TestGrafana(t *testing.T) {
 		},
 		{
 			`select @@version_comment limit 1`,
-			[][]string{{"NULL"}},
+			[][]string{{""}},
 		},
 		{
 			`describe table mytable`,

engine_test.go

@@ -650,6 +650,8 @@ var queries = []struct {
 			{"ndbinfo_version", ""},
 			{"sql_select_limit", math.MaxInt32},
 			{"transaction_isolation", "READ UNCOMMITTED"},
+			{"version", ""},
+			{"version_comment", ""},
 		},
 	},
 	{

sql/session.go

@@ -175,6 +175,8 @@ func DefaultSessionConfig() map[string]TypedValue {
 		"ndbinfo_version":          TypedValue{Text, ""},
 		"sql_select_limit":         TypedValue{Int32, math.MaxInt32},
 		"transaction_isolation":    TypedValue{Text, "READ UNCOMMITTED"},
+		"version":                  TypedValue{Text, ""},
+		"version_comment":          TypedValue{Text, ""},
 	}
 }
 

sql/type.go

@@ -315,7 +315,7 @@ func (t numberT) Type() query.Type {
 // SQL implements Type interface.
 func (t numberT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(t.t, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	switch t.t {
@@ -441,7 +441,7 @@ var TimestampLayouts = []string{
 // SQL implements Type interface.
 func (t timestampT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.Timestamp, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	v, err := t.Convert(v)
@@ -517,7 +517,7 @@ func (t dateT) Type() query.Type {
 
 func (t dateT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.Timestamp, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	v, err := t.Convert(v)
@@ -619,7 +619,7 @@ func (t textT) Type() query.Type {
 // SQL implements Type interface.
 func (t textT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.Text, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	v, err := t.Convert(v)
@@ -656,7 +656,7 @@ func (t booleanT) Type() query.Type {
 // SQL implements Type interface.
 func (t booleanT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.Bit, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	b := []byte{'0'}
@@ -716,7 +716,7 @@ func (t blobT) Type() query.Type {
 // SQL implements Type interface.
 func (t blobT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.Blob, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	v, err := t.Convert(v)
@@ -760,7 +760,7 @@ func (t jsonT) Type() query.Type {
 // SQL implements Type interface.
 func (t jsonT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.TypeJSON, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	v, err := t.Convert(v)
@@ -867,7 +867,7 @@ func (t arrayT) Type() query.Type {
 
 func (t arrayT) SQL(v interface{}) (sqltypes.Value, error) {
 	if v == nil {
-		return sqltypes.MakeTrusted(sqltypes.TypeJSON, nil), nil
+		return sqltypes.NULL, nil
 	}
 
 	v, err := t.Convert(v)

sql/type_test.go

@@ -13,7 +13,7 @@ func TestIsNull(t *testing.T) {
 	require.True(t, IsNull(nil))
 
 	n := numberT{sqltypes.Uint64}
-	require.Equal(t, sqltypes.MakeTrusted(sqltypes.Uint64, nil), mustSQL(n.SQL(nil)))
+	require.Equal(t, sqltypes.NULL, mustSQL(n.SQL(nil)))
 	require.Equal(t, sqltypes.NewUint64(0), mustSQL(n.SQL(uint64(0))))
 }