expr: Support unix_timestamp pushdown to TiKV (#59498)

close #59497

Author: xzhangxian1008

pkg/expression/expr_to_pb_test.go

@@ -1880,6 +1880,16 @@ func TestExprPushDownToTiKV(t *testing.T) {
 			retType:      types.NewFieldType(mysql.TypeLong),
 			args:         []Expression{NewStrConst("year"), datetimeColumn, datetimeColumn},
 		},
+		{
+			functionName: ast.UnixTimestamp,
+			retType:      types.NewFieldType(mysql.TypeLong),
+			args:         []Expression{datetimeColumn},
+		},
+		{
+			functionName: ast.UnixTimestamp,
+			retType:      types.NewFieldType(mysql.TypeNewDecimal),
+			args:         []Expression{stringColumn},
+		},
 	}
 
 	ctx = mock.NewContext()

pkg/expression/infer_pushdown.go

@@ -224,6 +224,11 @@ func scalarExprSupportedByTiKV(ctx EvalContext, sf *ScalarFunction) bool {
 		/*ast.InetNtoa, ast.InetAton, ast.Inet6Ntoa, ast.Inet6Aton, ast.IsIPv4, ast.IsIPv4Compat, ast.IsIPv4Mapped, ast.IsIPv6,*/
 		ast.UUID:
 
+		return true
+	case ast.UnixTimestamp:
+		if sf.Function.PbCode() == tipb.ScalarFuncSig_UnixTimestampCurrent {
+			return false
+		}
 		return true
 	// Rust use the llvm math functions, which have different precision with Golang/MySQL(cmath)
 	// open the following switchers if we implement them in coprocessor via `cmath`

pkg/expression/scalar_function_test.go

@@ -185,3 +185,15 @@ func TestScalarFunctionHash64Equals(t *testing.T) {
 	require.NotEqual(t, hasher1.Sum64(), hasher2.Sum64())
 	require.False(t, sf0.Equals(sf4))
 }
+
+// To test that when argument number is 0, unix_timestamp can not be pushed down to tikv
+func TestForbidUnixTimestampPushdown(t *testing.T) {
+	ctx := mock.NewContext()
+	fc := &unixTimestampFunctionClass{baseFunctionClass{ast.UnixTimestamp, 0, 1}}
+	bt, err := fc.getFunction(ctx, nil)
+	require.NoError(t, err)
+	sf := &ScalarFunction{
+		Function: bt,
+	}
+	require.False(t, scalarExprSupportedByTiKV(ctx, sf))
+}