From 8686c3150c5a36e256b2fffc976a8a45e44d15a4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Wed, 26 Jul 2023 13:37:02 +0000
Subject: [PATCH] Support for DECIMAL in Clickhouse

---
 lib/ClickHouse_Server.cpp                   | 49 ++++++++++++++++++++-
 test/tap/tests/test_clickhouse_server-t.cpp |  2 +
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/lib/ClickHouse_Server.cpp b/lib/ClickHouse_Server.cpp
index 7c53e31c7..32ebb7e2f 100644
--- a/lib/ClickHouse_Server.cpp
+++ b/lib/ClickHouse_Server.cpp
@@ -62,6 +62,36 @@
 
 using namespace clickhouse;
 
+std::string dec128_to_pchar(Int128 value, size_t scale) {
+// code borrowed from https://github.com/bderleta/php-clickhouse/blob/master/conversions.h
+	   bool sign = (value < 0);
+	   char buffer48[48];
+	   char* s = &buffer48[47];
+	   size_t w = 0;
+	   *(--s) = 0;
+	   if (sign)
+			   value = -value;
+	   while (value) {
+			   Int128 v = value;
+			   v %= 10;
+			   char c = (char)v;
+			   *(--s) = c + '0';
+			   if ((++w) == scale)
+					   *(--s) = '.';
+			   value /= 10;
+	   }
+	   while (w < scale) {
+			   *(--s) = '0';
+			   if ((++w) == scale)
+					   *(--s) = '.';
+	   }
+	   if (w == scale)
+			   *(--s) = '0';
+	   if (sign)
+			   *(--s) = '-';
+	   return std::string(s);
+}
+
 __thread MySQL_Session * clickhouse_thread___mysql_sess;
 
 inline void ClickHouse_to_MySQL(const Block& block) {
@@ -99,7 +129,7 @@ inline void ClickHouse_to_MySQL(const Block& block) {
 #endif // CXX17
 			}
 
-			if (cc >= clickhouse::Type::Code::Int8 && cc <= clickhouse::Type::Code::Float64) {
+			if (cc >= clickhouse::Type::Code::Int8 && cc <= clickhouse::Type::Code::Decimal128) {
 				bool _unsigned = false;
 				uint16_t flags = is_null | 128;
 
@@ -151,6 +181,14 @@ inline void ClickHouse_to_MySQL(const Block& block) {
 						size = 22;
 						decimals = 31;
 						break;
+					case clickhouse::Type::Code::Decimal:
+					case clickhouse::Type::Code::Decimal32:
+					case clickhouse::Type::Code::Decimal64:
+					case clickhouse::Type::Code::Decimal128:
+						type = MYSQL_TYPE_NEWDECIMAL;
+						size = 32;
+						decimals = 31;
+						break;
 					default:
 						_unsigned = false;
 						flags = 128;
@@ -237,6 +275,15 @@ inline void ClickHouse_to_MySQL(const Block& block) {
 				case clickhouse::Type::Code::Float64:
 					s=std::to_string(block[i]->As<ColumnFloat64>()->At(r));
 					break;
+				case clickhouse::Type::Code::Decimal:
+				case clickhouse::Type::Code::Decimal32:
+				case clickhouse::Type::Code::Decimal64:
+				case clickhouse::Type::Code::Decimal128:
+					{
+						size_t scale = block[i]->Type()->As<DecimalType>()->GetScale();
+						s = dec128_to_pchar(block[i]->As<ColumnDecimal>()->At(r), scale);
+					}
+					break;
 				case clickhouse::Type::Code::Enum8:
 					s=block[i]->As<ColumnEnum8>()->NameAt(r);;
 					break;
diff --git a/test/tap/tests/test_clickhouse_server-t.cpp b/test/tap/tests/test_clickhouse_server-t.cpp
index 6f7028880..f844c1e39 100644
--- a/test/tap/tests/test_clickhouse_server-t.cpp
+++ b/test/tap/tests/test_clickhouse_server-t.cpp
@@ -253,6 +253,8 @@ std::vector<query_spec> queries_set1 {
 	std::make_tuple<std::string, int>("SELECT NULL AS a", 0, 1),
 	std::make_tuple<std::string, int>("SELECT NULL+2 AS a, 'hello', NULL+1, 'world', NULL AS b", 0, 1),
 	std::make_tuple<std::string, int>("SELECT CONCAT('AAA',NULL)", 0, 1),
+	std::make_tuple<std::string, int>("SELECT CAST(-1234.1234, 'Decimal32(3)')", 0, 1),
+	std::make_tuple<std::string, int>("SELECT CAST(1000.0, 'Decimal128(3)')", 0, 1),
 	std::make_tuple<std::string, int>("DROP TABLE IF EXISTS table1", 0, -1),
 	std::make_tuple<std::string, int>("CREATE TABLE table1 (CounterID INT, EventDate DATE, col1 INT) ENGINE=MergeTree(EventDate, (CounterID, EventDate), 8192)", 0, -1),
 	std::make_tuple<std::string, int>("CREATE TABLE table1 (CounterID INT, EventDate DATE, col1 INT) ENGINE=MergeTree(EventDate, (CounterID, EventDate), 8192)", 1148, -1), // the second time it must fails