From ee51907a2f21686e96774a58d687d1ff5249b9a8 Mon Sep 17 00:00:00 2001
From: Will Hinson <wmhcell@gmail.com>
Date: Thu, 16 May 2024 00:03:36 -0400
Subject: [PATCH] Implemented support for the SQL Server sql_variant data type

---
 src/dbspecific.h |  1 +
 src/getdata.cpp  | 32 ++++++++++++++++++++++++++++++++
 src/pyodbc.h     |  4 ++++
 3 files changed, 37 insertions(+)

diff --git a/src/dbspecific.h b/src/dbspecific.h
index d9bc4dc4..e6af0a93 100644
--- a/src/dbspecific.h
+++ b/src/dbspecific.h
@@ -11,6 +11,7 @@
 // SQL Server
 
 
+#define SQL_SS_VARIANT -150     // SQL Server 2008 SQL_VARIANT type
 #define SQL_SS_XML -152         // SQL Server 2005 XML type
 #define SQL_DB2_DECFLOAT -360   // IBM DB/2 DECFLOAT type
 #define SQL_DB2_XML -370        // IBM DB/2 XML type
diff --git a/src/getdata.cpp b/src/getdata.cpp
index 626f41b1..3831c5d9 100644
--- a/src/getdata.cpp
+++ b/src/getdata.cpp
@@ -38,6 +38,7 @@ void GetData_init()
 }
 
 static byte* ReallocOrFreeBuffer(byte* pb, Py_ssize_t cbNeed);
+PyObject *GetData_SqlVariant(Cursor *cur, Py_ssize_t iCol);
 
 inline bool IsBinaryType(SQLSMALLINT sqltype)
 {
@@ -751,8 +752,39 @@ PyObject* GetData(Cursor* cur, Py_ssize_t iCol)
 
     case SQL_SS_TIME2:
         return GetSqlServerTime(cur, iCol);
+
+    case SQL_SS_VARIANT:
+        return GetData_SqlVariant(cur, iCol);
     }
 
     return RaiseErrorV("HY106", ProgrammingError, "ODBC SQL type %d is not yet supported.  column-index=%zd  type=%d",
                        (int)pinfo->sql_type, iCol, (int)pinfo->sql_type);
 }
+
+PyObject *GetData_SqlVariant(Cursor *cur, Py_ssize_t iCol) {
+    char pBuff;
+
+    SQLLEN indicator, variantType;
+    SQLRETURN retcode;
+
+    // Call SQLGetData on the current column with a data length of 0. According to MS, this makes
+    // the ODBC driver read the sql_variant header which contains the underlying data type
+    pBuff = 0;
+    indicator = 0;
+    retcode = SQLGetData(cur->hstmt, static_cast<SQLSMALLINT>(iCol + 1), SQL_C_BINARY,   
+                                    &pBuff, 0, &indicator);
+    if (!SQL_SUCCEEDED(retcode))
+        return RaiseErrorFromHandle(cur->cnxn, "SQLGetData", cur->cnxn->hdbc, cur->hstmt);
+
+    // Get the SQL_CA_SS_VARIANT_TYPE field for the column which will contain the underlying data type
+    variantType = 0;
+    retcode = SQLColAttribute(cur->hstmt, iCol + 1, SQL_CA_SS_VARIANT_TYPE, NULL, 0, NULL, &variantType);
+    if (!SQL_SUCCEEDED(retcode))
+        return RaiseErrorFromHandle(cur->cnxn, "SQLColAttribute", cur->cnxn->hdbc, cur->hstmt);
+
+    // Replace the original SQL_VARIANT data type with the underlying data type then call GetData() again
+    cur->colinfos[iCol].sql_type = static_cast<SQLSMALLINT>(variantType);
+    return GetData(cur, iCol);
+
+    // NOTE: we don't free the hstmt here as it's managed by the cursor
+}
diff --git a/src/pyodbc.h b/src/pyodbc.h
index a18529e9..9ef2bd77 100644
--- a/src/pyodbc.h
+++ b/src/pyodbc.h
@@ -76,6 +76,10 @@ typedef unsigned long long UINT64;
 #define SQL_CA_SS_CATALOG_NAME 1225
 #endif
 
+#ifndef SQL_CA_SS_VARIANT_TYPE
+#define SQL_CA_SS_VARIANT_TYPE 1215
+#endif
+
 inline bool IsSet(DWORD grf, DWORD flags)
 {
     return (grf & flags) == flags;