diff --git a/document-store/src/integrationTest/java/org/hypertrace/core/documentstore/FlatCollectionWriteTest.java b/document-store/src/integrationTest/java/org/hypertrace/core/documentstore/FlatCollectionWriteTest.java
index 45ce51cc..f2eead58 100644
--- a/document-store/src/integrationTest/java/org/hypertrace/core/documentstore/FlatCollectionWriteTest.java
+++ b/document-store/src/integrationTest/java/org/hypertrace/core/documentstore/FlatCollectionWriteTest.java
@@ -4,6 +4,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -667,7 +668,8 @@ public Stream<? extends Arguments> provideArguments(ExtensionContext context) {
   class CreateOrReplaceTests {
 
     @Test
-    @DisplayName("Should create new document and return true")
+    @DisplayName(
+        "Should create new document and return true. Cols not specified should be set of default NULL")
     void testCreateOrReplaceNewDocument() throws Exception {
 
       String docId = getRandomDocId(4);
@@ -691,6 +693,10 @@ void testCreateOrReplaceNewDocument() throws Exception {
             assertEquals("New Upsert Item", rs.getString("item"));
             assertEquals(500, rs.getInt("price"));
             assertEquals(25, rs.getInt("quantity"));
+            // assert on some fields that they're set to null correctly
+            assertNull(rs.getObject("sales"));
+            assertNull(rs.getObject("categoryTags"));
+            assertNull(rs.getObject("date"));
           });
     }
 
@@ -714,7 +720,6 @@ void testCreateOrReplaceExistingDocument() throws Exception {
       ObjectNode updatedNode = OBJECT_MAPPER.createObjectNode();
       updatedNode.put("id", docId);
       updatedNode.put("item", "Updated Item");
-      updatedNode.put("price", 999);
       updatedNode.put("quantity", 50);
       Document updatedDoc = new JSONDocument(updatedNode);
 
@@ -727,7 +732,8 @@ void testCreateOrReplaceExistingDocument() throws Exception {
           rs -> {
             assertTrue(rs.next());
             assertEquals("Updated Item", rs.getString("item"));
-            assertEquals(999, rs.getInt("price"));
+            // this should be the default since price is not present in the updated document
+            assertNull(rs.getObject("price"));
             assertEquals(50, rs.getInt("quantity"));
           });
     }
diff --git a/document-store/src/main/java/org/hypertrace/core/documentstore/postgres/FlatPostgresCollection.java b/document-store/src/main/java/org/hypertrace/core/documentstore/postgres/FlatPostgresCollection.java
index 0de58c79..246db7df 100644
--- a/document-store/src/main/java/org/hypertrace/core/documentstore/postgres/FlatPostgresCollection.java
+++ b/document-store/src/main/java/org/hypertrace/core/documentstore/postgres/FlatPostgresCollection.java
@@ -862,7 +862,14 @@ private boolean createOrReplaceWithRetry(Key key, Document document, boolean isR
       PostgresDataType pkType = getPrimaryKeyType(tableName, pkColumn);
       parsed.add(quotedPkColumn, key.toString(), pkType, false);
 
-      String sql = buildUpsertSql(parsed.getColumns(), quotedPkColumn);
+      List<String> docColumns = parsed.getColumns();
+      List<String> allColumns =
+          schemaRegistry.getSchema(tableName).values().stream()
+              .map(PostgresColumnMetadata::getName)
+              .map(PostgresUtils::wrapFieldNamesWithDoubleQuotes)
+              .collect(Collectors.toList());
+
+      String sql = buildCreateOrReplaceSql(allColumns, docColumns, quotedPkColumn);
       LOGGER.debug("Upsert SQL: {}", sql);
 
       return executeUpsert(sql, parsed);
@@ -882,15 +889,16 @@ private boolean createOrReplaceWithRetry(Key key, Document document, boolean isR
    *
    * <ul>
    *   <li>Inserts a new row if no conflict on the primary key
-   *   <li>Updates all non-PK columns if a row with the same PK already exists
+   *   <li>If the row with that PK already exists, it is replaced in entirety. Cols not present in
+   *       the latest upsert are set to their default values (as defined in the schema)
    * </ul>
    *
    * <p><b>Generated SQL pattern:</b>
    *
    * <pre>{@code
-   * INSERT INTO table (col1, col2, pk_col)
+   * INSERT INTO table (col1, col2,, col3, pk_col)
    * VALUES (?, ?, ?)
-   * ON CONFLICT (pk_col) DO UPDATE SET col1 = EXCLUDED.col1, col2 = EXCLUDED.col2
+   * ON CONFLICT (pk_col) DO UPDATE SET col1 = EXCLUDED.col1, col2 = EXCLUDED.col2, col3 = DEFAULT
    * RETURNING (xmax = 0) AS is_insert
    * }</pre>
    *
@@ -909,19 +917,30 @@ private boolean createOrReplaceWithRetry(Key key, Document document, boolean isR
    *   <li>Thus, {@code is_insert = true} means INSERT, {@code is_insert = false} means UPDATE
    * </ul>
    *
-   * @param columns List of quoted column names to include in the upsert (including PK)
+   * @param allTableColumns all cols present in the table
+   * @param docColumns cols present in the document
    * @param pkColumn The quoted primary key column name used for conflict detection
    * @return The complete upsert SQL statement with placeholders for values
    */
-  private String buildUpsertSql(List<String> columns, String pkColumn) {
-    String columnList = String.join(", ", columns);
-    String placeholders = String.join(", ", columns.stream().map(c -> "?").toArray(String[]::new));
-
-    // Build SET clause for non-PK columns: col = EXCLUDED.col
+  private String buildCreateOrReplaceSql(
+      List<String> allTableColumns, List<String> docColumns, String pkColumn) {
+    String columnList = String.join(", ", docColumns);
+    String placeholders =
+        String.join(", ", docColumns.stream().map(c -> "?").toArray(String[]::new));
+    Set<String> docColumnsSet = new HashSet<>(docColumns);
+
+    // Build SET clause for non-PK columns.
     String setClause =
-        columns.stream()
+        allTableColumns.stream()
             .filter(col -> !col.equals(pkColumn))
-            .map(col -> col + " = EXCLUDED." + col)
+            .map(
+                col -> {
+                  if (docColumnsSet.contains(col)) {
+                    return col + " = EXCLUDED." + col;
+                  } else {
+                    return col + " = DEFAULT";
+                  }
+                })
             .collect(Collectors.joining(", "));
 
     return String.format(