fix text storage for left and instr function (#3018)

Author: jycor

enginetest/memory_engine_test.go

@@ -226,7 +226,7 @@ func TestSingleScript(t *testing.T) {
 
 	for _, test := range scripts {
 		harness := enginetest.NewMemoryHarness("", 1, testNumPartitions, true, nil)
-		harness.UseServer()
+		//harness.UseServer()
 		engine, err := harness.NewEngine(t)
 		if err != nil {
 			panic(err)

enginetest/queries/script_queries.go

@@ -8684,6 +8684,34 @@ where
 			},
 		},
 	},
+	{
+		Name:    "substring function tests with wrappers",
+		Dialect: "mysql",
+		SetUpScript: []string{
+			"create table tbl (t text);",
+			"insert into tbl values ('abcdef');",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query: "select left(t, 3) from tbl;",
+				Expected: []sql.Row{
+					{"abc"},
+				},
+			},
+			{
+				Query: "select right(t, 3) from tbl;",
+				Expected: []sql.Row{
+					{"def"},
+				},
+			},
+			{
+				Query: "select instr(t, 'bcd') from tbl;",
+				Expected: []sql.Row{
+					{2},
+				},
+			},
+		},
+	},
 }
 
 var SpatialScriptTests = []ScriptTest{

sql/expression/function/substring.go

@@ -349,8 +349,20 @@ func (l Left) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	switch str := str.(type) {
 	case string:
 		text = []rune(str)
+	case sql.StringWrapper:
+		s, err := str.Unwrap(ctx)
+		if err != nil {
+			return nil, err
+		}
+		text = []rune(s)
 	case []byte:
 		text = []rune(string(str))
+	case sql.BytesWrapper:
+		b, err := str.Unwrap(ctx)
+		if err != nil {
+			return nil, err
+		}
+		text = []rune(string(b))
 	case nil:
 		return nil, nil
 	default:
@@ -583,8 +595,20 @@ func (i Instr) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	switch str := str.(type) {
 	case string:
 		text = []rune(str)
+	case sql.StringWrapper:
+		s, err := str.Unwrap(ctx)
+		if err != nil {
+			return nil, err
+		}
+		text = []rune(s)
 	case []byte:
 		text = []rune(string(str))
+	case sql.BytesWrapper:
+		s, err := str.Unwrap(ctx)
+		if err != nil {
+			return nil, err
+		}
+		text = []rune(string(s))
 	case nil:
 		return nil, nil
 	default:
@@ -600,8 +624,20 @@ func (i Instr) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	switch substr := substr.(type) {
 	case string:
 		subtext = []rune(substr)
+	case sql.StringWrapper:
+		s, err := substr.Unwrap(ctx)
+		if err != nil {
+			return nil, err
+		}
+		text = []rune(s)
 	case []byte:
-		subtext = []rune(string(subtext))
+		subtext = []rune(string(substr))
+	case sql.BytesWrapper:
+		s, err := substr.Unwrap(ctx)
+		if err != nil {
+			return nil, err
+		}
+		subtext = []rune(string(s))
 	case nil:
 		return nil, nil
 	default: