expression: Add json_extract, cast(json as string), json_unquote push…

… down support for tiflash (pingcap#39533)

ref pingcap/tiflash#6376, close pingcap#39458

expression/expr_to_pb_test.go

@@ -528,6 +528,18 @@ func TestExprPushDownToFlash(t *testing.T) {
 	require.NoError(t, err)
 	exprs = append(exprs, function)
 
+	// json_extract
+	function, err = NewFunction(mock.NewContext(), ast.JSONExtract, types.NewFieldType(mysql.TypeJSON), jsonColumn, stringColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
+	// json_unquote argument is cast(json as string)
+	subFunc, subErr := NewFunction(mock.NewContext(), ast.Cast, types.NewFieldType(mysql.TypeString), jsonColumn)
+	require.NoError(t, subErr)
+	function, err = NewFunction(mock.NewContext(), ast.JSONUnquote, types.NewFieldType(mysql.TypeString), subFunc)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
 	// lpad
 	function, err = NewFunction(mock.NewContext(), ast.Lpad, types.NewFieldType(mysql.TypeString), stringColumn, int32Column, stringColumn)
 	require.NoError(t, err)
@@ -639,6 +651,11 @@ func TestExprPushDownToFlash(t *testing.T) {
 	require.NoError(t, err)
 	exprs = append(exprs, function)
 
+	// CastJsonAsString
+	function, err = NewFunction(mock.NewContext(), ast.Cast, types.NewFieldType(mysql.TypeString), jsonColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
 	// CastIntAsTime
 	function, err = NewFunction(mock.NewContext(), ast.Cast, types.NewFieldType(mysql.TypeDatetime), intColumn)
 	require.NoError(t, err)
@@ -958,6 +975,11 @@ func TestExprPushDownToFlash(t *testing.T) {
 
 	exprs = exprs[:0]
 
+	// json_unquote's argument is not cast(json as string)
+	function, err = NewFunction(mock.NewContext(), ast.JSONUnquote, types.NewFieldType(mysql.TypeString), stringColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
 	// Substring2Args: can not be pushed
 	function, err = NewFunction(mock.NewContext(), ast.Substr, types.NewFieldType(mysql.TypeString), binaryStringColumn, intColumn)
 	require.NoError(t, err)

expression/expression.go

@@ -1150,7 +1150,7 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 
 		ast.Sqrt, ast.Log, ast.Log2, ast.Log10, ast.Ln, ast.Exp, ast.Pow, ast.Sign,
 		ast.Radians, ast.Degrees, ast.Conv, ast.CRC32,
-		ast.JSONLength, ast.Repeat,
+		ast.JSONLength, ast.JSONExtract, ast.JSONUnquote, ast.Repeat,
 		ast.InetNtoa, ast.InetAton, ast.Inet6Ntoa, ast.Inet6Aton,
 		ast.Coalesce, ast.ASCII, ast.Length, ast.Trim, ast.Position, ast.Format, ast.Elt,
 		ast.LTrim, ast.RTrim, ast.Lpad, ast.Rpad,
@@ -1163,6 +1163,12 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 			tipb.ScalarFuncSig_IfDuration,
 			tipb.ScalarFuncSig_CaseWhenDuration:
 			return false
+		case tipb.ScalarFuncSig_JsonUnquoteSig:
+			// TiFlash json_unquote now only supports json string generated by cast(json as string)
+			if childFunc, ok := function.GetArgs()[0].(*ScalarFunction); ok {
+				return childFunc.Function.PbCode() == tipb.ScalarFuncSig_CastJsonAsString
+			}
+			return false
 		}
 		return true
 	case ast.Regexp, ast.RegexpLike, ast.RegexpInStr, ast.RegexpSubstr:
@@ -1200,7 +1206,7 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 			tipb.ScalarFuncSig_CastStringAsDecimal /*, tipb.ScalarFuncSig_CastDurationAsDecimal, tipb.ScalarFuncSig_CastJsonAsDecimal*/ :
 			return function.RetType.IsDecimalValid()
 		case tipb.ScalarFuncSig_CastDecimalAsString, tipb.ScalarFuncSig_CastIntAsString, tipb.ScalarFuncSig_CastRealAsString, tipb.ScalarFuncSig_CastTimeAsString,
-			tipb.ScalarFuncSig_CastStringAsString /*, tipb.ScalarFuncSig_CastDurationAsString, tipb.ScalarFuncSig_CastJsonAsString*/ :
+			tipb.ScalarFuncSig_CastStringAsString, tipb.ScalarFuncSig_CastJsonAsString /*, tipb.ScalarFuncSig_CastDurationAsString*/ :
 			return true
 		case tipb.ScalarFuncSig_CastDecimalAsTime, tipb.ScalarFuncSig_CastIntAsTime, tipb.ScalarFuncSig_CastRealAsTime, tipb.ScalarFuncSig_CastTimeAsTime,
 			tipb.ScalarFuncSig_CastStringAsTime /*, tipb.ScalarFuncSig_CastDurationAsTime, tipb.ScalarFuncSig_CastJsonAsTime*/ :