Improve merge error logging; disable sync deletes (WHEN NOT MATCHED BY SOURCE) (#119)

- Wrap MergeData in try-catch and log scope, statement, and exception before rethrow
- Omit WHEN NOT MATCHED BY SOURCE THEN DELETE from merge so target rows are not deleted when missing in source

Author: devlead

src/SqlBulkSyncFunction/Helpers/SqlCommandExtensions.cs

@@ -64,11 +64,19 @@ public static void MergeData(
         ILogger logger
         )
     {
-        var rowCount = targetConn.Query<long>(
-            commandTimeout: 500000,
-            sql: tableSchema.MergeNewOrUpdateStatement
-            ).First();
-        logger.LogInformation("{Scope} {RowCount} records merged", scope, rowCount);
+        try
+        {
+            var rowCount = targetConn.Query<long>(
+                commandTimeout: 500000,
+                sql: tableSchema.MergeNewOrUpdateStatement
+                ).First();
+            logger.LogInformation("{Scope} {RowCount} records merged", scope, rowCount);
+        }
+        catch(Exception ex)
+        {
+            logger.LogError(ex, "Merge failed for {Scope} with statement {MergeNewOrUpdateStatement}\r\n{Exception}", scope, tableSchema.MergeNewOrUpdateStatement, ex.Message);
+            throw;
+        }
     }
 
     public static void DeleteData(

src/SqlBulkSyncFunction/Helpers/SqlStatementExtensions.cs

@@ -121,11 +121,12 @@ THEN UPDATE
                 ),
             (
                 (tableSchema.TargetVersion.CurrentVersion < 0)
-                    ? """
+                    ? string.Empty
+                        //"""
 
-                    WHEN NOT MATCHED BY SOURCE
-                        THEN DELETE
-                    """
+                        //WHEN NOT MATCHED BY SOURCE
+                        //    THEN DELETE
+                        //"""
                     : string.Empty
                 ),
             (