Re: [PR] IGNITE-18883: Bug. Potentially incorrect definition of rows to insert for MERGE [ignite-3]

["korlov42 (via GitHub)" <gi...@apache.org>]

korlov42 commented on code in PR #4155:
URL: https://github.com/apache/ignite-3/pull/4155#discussion_r1701849664


##########
modules/sql-engine/src/main/java/org/apache/ignite/internal/sql/engine/exec/rel/ModifyNode.java:
##########
@@ -361,10 +361,20 @@ private static int[] applyOffset(int[] srcMapping, int offset) {
             rowsToUpdate = new ArrayList<>();
 
             for (RowT row : rows) {
-                // this check doesn't seem correct because NULL could be a legit value for column,
-                // but this is how it was implemented before, so I just file an issue to deal with this later
-                // TODO: https://issues.apache.org/jira/browse/IGNITE-18883
-                if (handler.get(updateColumnOffset, row) == null) {
+                // Merge operation uses a left join as its input, so in order to distinguish between new rows and modified rows
+                // (rows produced by WHEN MATCHED, and rows produces by WHEN NOT MATCHED clauses)
+                // we need to check all columns of a destination table for null values.
+                //
+                // Since every table has a primary key and all primary keys columns are not nullable, we can assume that
+                // a row is produced by the WHEN NOT MATCHED clause iff every column in the subset of input columns
+                // that belongs to the destination table has a NULL value. Otherwise it belongs to the WHEN MATCH clause.
+
+                boolean insertRow = true;
+                for (int i = updateColumnOffset; i < updateColumnOffset + mapping.length; i++) {
+                    insertRow = insertRow && handler.get(i, row) == null;

Review Comment:
   ```suggestion
                       if (!handler.isNull(i, row)) {
                           insertRow = false;
   
                           break;
                       }
   ```



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