Merge pull request #11901 from BohuTANG/mysql_global_variables

Change MySQL global variables query to globalVariable function

src/Functions/globalVariable.cpp

@@ -1,11 +1,15 @@
 #include <Functions/IFunctionImpl.h>
 #include <Functions/FunctionFactory.h>
 #include <Functions/FunctionHelpers.h>
+#include <DataTypes/DataTypesNumber.h>
 #include <DataTypes/DataTypeString.h>
 #include <Columns/ColumnString.h>
 #include <Columns/ColumnConst.h>
 #include <Core/Field.h>
 
+#include <unordered_map>
+#include <Poco/String.h>
+
 
 namespace DB
 {
@@ -43,19 +47,38 @@ public:
     DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
     {
         if (!checkColumnConst<ColumnString>(arguments[0].column.get()))
-            throw Exception("Agrument of function " + getName() + " must be constant string", ErrorCodes::BAD_ARGUMENTS);
+            throw Exception("Argument of function " + getName() + " must be constant string", ErrorCodes::BAD_ARGUMENTS);
 
         String variable_name = assert_cast<const ColumnConst &>(*arguments[0].column).getValue<String>();
-
-        throw Exception("There is no global variable with name " + variable_name, ErrorCodes::BAD_ARGUMENTS);
+        auto variable = global_variable_map.find(Poco::toLower(variable_name));
+        if (variable == global_variable_map.end())
+            return std::make_shared<DataTypeInt32>();
+        else
+            return variable->second.type;
     }
 
-    void executeImpl(Block & block, const ColumnNumbers &, size_t /*result*/, size_t /*input_rows_count*/) override
+    void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
     {
-        String variable_name = assert_cast<const ColumnConst &>(*block.getByPosition(0).column).getValue<String>();
+        const ColumnWithTypeAndName & col = block.getByPosition(arguments[0]);
+        String variable_name = assert_cast<const ColumnConst &>(*col.column).getValue<String>();
+        auto variable = global_variable_map.find(Poco::toLower(variable_name));
 
-        throw Exception("There is no global variable with name " + variable_name, ErrorCodes::BAD_ARGUMENTS);
+        Field val = 0;
+        if (variable != global_variable_map.end())
+            val = variable->second.value;
+
+        auto & result_col = block.getByPosition(result);
+        result_col.column = result_col.type->createColumnConst(input_rows_count, val);
     }
+
+private:
+    struct TypeAndValue
+    {
+        DataTypePtr type;
+        Field value;
+    };
+    std::unordered_map<String, TypeAndValue> global_variable_map = {
+        {"max_allowed_packet", {std::make_shared<DataTypeInt32>(), 67108864}}, {"version", {std::make_shared<DataTypeString>(), "5.7.30"}}};
 };
 
 

src/Parsers/ExpressionElementParsers.cpp

@@ -1270,6 +1270,20 @@ bool ParserMySQLGlobalVariable::parseImpl(Pos & pos, ASTPtr & node, Expected & e
     String name(pos->begin, pos->end);
     ++pos;
 
+    /// SELECT @@session|global.variable style
+    if (pos->type == TokenType::Dot)
+    {
+        ++pos;
+
+        if (pos->type != TokenType::BareWord)
+        {
+            expected.add(pos, "variable name");
+            return false;
+        }
+        name = String(pos->begin, pos->end);
+        ++pos;
+    }
+
     auto name_literal = std::make_shared<ASTLiteral>(name);
 
     auto expr_list_args = std::make_shared<ASTExpressionList>();
@@ -1281,6 +1295,7 @@ bool ParserMySQLGlobalVariable::parseImpl(Pos & pos, ASTPtr & node, Expected & e
     function_node->children.push_back(expr_list_args);
 
     node = function_node;
+    node->setAlias("@@" + name);
     return true;
 }
 

src/Server/MySQLHandler.cpp

@@ -271,7 +271,6 @@ void MySQLHandler::comPing()
 }
 
 static bool isFederatedServerSetupSetCommand(const String & query);
-static bool isFederatedServerSetupSelectVarCommand(const String & query);
 
 void MySQLHandler::comQuery(ReadBuffer & payload)
 {
@@ -289,15 +288,6 @@ void MySQLHandler::comQuery(ReadBuffer & payload)
         bool should_replace = false;
         bool with_output = false;
 
-        // Translate query from MySQL to ClickHouse.
-        // Required parameters when setup:
-        // * max_allowed_packet, default 64MB, https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_max_allowed_packet
-        if (isFederatedServerSetupSelectVarCommand(query))
-        {
-            should_replace = true;
-            replacement_query = "SELECT 67108864 AS max_allowed_packet";
-        }
-
         // This is a workaround in order to support adding ClickHouse to MySQL using federated server.
         if (0 == strncasecmp("SHOW TABLE STATUS LIKE", query.c_str(), 22))
         {
@@ -305,6 +295,11 @@ void MySQLHandler::comQuery(ReadBuffer & payload)
             replacement_query = boost::replace_all_copy(query, "SHOW TABLE STATUS LIKE ", show_table_status_replacement_query);
         }
 
+        if (0 == strncasecmp("SHOW VARIABLES", query.c_str(), 13))
+        {
+            should_replace = true;
+        }
+
         ReadBufferFromString replacement(replacement_query);
 
         Context query_context = connection_context;
@@ -377,16 +372,6 @@ static bool isFederatedServerSetupSetCommand(const String & query)
     return 1 == std::regex_match(query, expr);
 }
 
-static bool isFederatedServerSetupSelectVarCommand(const String & query)
-{
-     static const std::regex expr{
-         "|(^(SELECT @@(.*)))"
-         "|(^((/\\*(.*)\\*/)([ \t]*)(SELECT([ \t]*)@@(.*))))"
-         "|(^((/\\*(.*)\\*/)([ \t]*)(SHOW VARIABLES(.*))))"
-         , std::regex::icase};
-     return 1 == std::regex_match(query, expr);
-}
-
 const String MySQLHandler::show_table_status_replacement_query("SELECT"
                                                                " name AS Name,"
                                                                " engine AS Engine,"

tests/queries/0_stateless/01337_mysql_global_variables.reference

@@ -0,0 +1,15 @@
+0
+"@@max_allowed_packet"
+67108864
+"@@MAX_ALLOWED_PACKET"
+67108864
+"@@max_allowed_packet","number"
+67108864,0
+67108864,1
+67108864,2
+"@@auto_increment_increment"
+0
+"auto_increment_increment"
+0
+"@@Version"
+"5.7.30"

tests/queries/0_stateless/01337_mysql_global_variables.sql

@@ -1 +1,7 @@
-SELECT @@test; -- { serverError 36 }
+SELECT @@test;
+SELECT @@max_allowed_packet FORMAT CSVWithNames;
+SELECT @@MAX_ALLOWED_PACKET FORMAT CSVWithNames;
+SELECT @@max_allowed_packet, number FROM system.numbers LIMIT 3 FORMAT CSVWithNames;
+SELECT @@session.auto_increment_increment FORMAT CSVWithNames;
+SELECT @@session.auto_increment_increment AS auto_increment_increment FORMAT CSVWithNames;
+SELECT @@Version FORMAT CSVWithNames;