Support decimal for sql execution.

decimal.go

@@ -0,0 +1,5 @@
+package mysql
+
+type Decimal interface {
+	DecimalString() string
+}

packets.go

@@ -1102,6 +1102,21 @@ func (stmt *mysqlStmt) writeExecutePacket(args []driver.Value) error {
 					}
 				}
 
+			case Decimal:
+				paramTypes[i+i] = byte(fieldTypeNewDecimal)
+				paramTypes[i+i+1] = 0x00
+
+				if len(v.DecimalString()) < longDataSize {
+					paramValues = appendLengthEncodedInteger(paramValues,
+						uint64(len(v.DecimalString())),
+					)
+					paramValues = append(paramValues, v.DecimalString()...)
+				} else {
+					if err := stmt.writeCommandLongData(i, []byte(v.DecimalString())); err != nil {
+						return err
+					}
+				}
+
 			case time.Time:
 				paramTypes[i+i] = byte(fieldTypeString)
 				paramTypes[i+i+1] = 0x00

statement.go

@@ -141,6 +141,10 @@ func (c converter) ConvertValue(v interface{}) (driver.Value, error) {
 		return v, nil
 	}
 
+	if _, ok := v.(Decimal); ok {
+		return v, nil
+	}
+
 	if vr, ok := v.(driver.Valuer); ok {
 		sv, err := callValuerValue(vr)
 		if err != nil {