Address comment from Rob and add SQLDisconnect test case

Author: alinaliBQ

cpp/src/arrow/flight/sql/odbc/odbc_api.cc

@@ -395,9 +395,8 @@ SQLRETURN SQLConnectW(SQLHDBC conn, SQLWCHAR* dsnName, SQLSMALLINT dsnNameLen,
 
   using ODBC::SqlWcharToString;
 
-  ODBCConnection* connection = reinterpret_cast<ODBCConnection*>(conn);
-
   return ODBCConnection::ExecuteWithDiagnostics(conn, SQL_ERROR, [=]() {
+    ODBCConnection* connection = reinterpret_cast<ODBCConnection*>(conn);
     std::string dsn = SqlWcharToString(dsnName, dsnNameLen);
 
     Configuration config;

cpp/src/arrow/flight/sql/odbc/tests/connection_test.cc

@@ -709,6 +709,44 @@ TEST(SQLConnect, TestSQLConnectDSNPrecedence) {
 
   EXPECT_TRUE(ret == SQL_SUCCESS);
 }
+
+TEST(SQLDisconnect, TestSQLDisconnectWithoutConnection) {
+  // ODBC Environment
+  SQLHENV env;
+  SQLHDBC conn;
+
+  // Allocate an environment handle
+  SQLRETURN ret = SQLAllocEnv(&env);
+
+  EXPECT_TRUE(ret == SQL_SUCCESS);
+
+  ret = SQLSetEnvAttr(env, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0);
+
+  EXPECT_TRUE(ret == SQL_SUCCESS);
+
+  // Allocate a connection using alloc handle
+  ret = SQLAllocHandle(SQL_HANDLE_DBC, env, &conn);
+
+  EXPECT_TRUE(ret == SQL_SUCCESS);
+
+  // Attempt to disconnect without a connection, expect to fail
+  ret = SQLDisconnect(conn);
+
+  EXPECT_TRUE(ret == SQL_ERROR);
+
+  // Expect ODBC driver manager to return error state
+  VerifyOdbcErrorState(SQL_HANDLE_DBC, conn, std::string("08003"));
+
+  // Free connection handle
+  ret = SQLFreeHandle(SQL_HANDLE_DBC, conn);
+
+  EXPECT_TRUE(ret == SQL_SUCCESS);
+
+  // Free environment handle
+  ret = SQLFreeHandle(SQL_HANDLE_ENV, env);
+
+  EXPECT_TRUE(ret == SQL_SUCCESS);
+}
 }  // namespace integration_tests
 }  // namespace odbc
 }  // namespace flight