fix: PostgreSQL compatibility for diagrams and date functions

- Fix Diagram node discovery to handle PostgreSQL double-quote format
- Fix indexes dict to filter out None column names
- Add null check for heading.indexes in describe()
- Add TIMESTAMPDIFF translation (YEAR, MONTH, DAY units)
- Add CURDATE() → CURRENT_DATE translation
- Add NOW() → CURRENT_TIMESTAMP translation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/adapters/postgres.py

@@ -1046,6 +1046,36 @@ def replace_group_concat(match):
 
         expr = re.sub(r"GROUP_CONCAT\s*\((.+?)\)", replace_group_concat, expr, flags=re.IGNORECASE)
 
+        # TIMESTAMPDIFF(YEAR, d1, d2) → EXTRACT(YEAR FROM AGE(d2, d1))::int
+        # TIMESTAMPDIFF(MONTH, d1, d2) → year*12 + month from AGE
+        # TIMESTAMPDIFF(DAY, d1, d2) → (d2::date - d1::date)
+        def replace_timestampdiff(match):
+            unit = match.group(1).upper()
+            date1 = match.group(2).strip()
+            date2 = match.group(3).strip()
+            if unit == "YEAR":
+                return f"EXTRACT(YEAR FROM AGE({date2}, {date1}))::int"
+            elif unit == "MONTH":
+                return f"(EXTRACT(YEAR FROM AGE({date2}, {date1})) * 12 + EXTRACT(MONTH FROM AGE({date2}, {date1})))::int"
+            elif unit == "DAY":
+                return f"({date2}::date - {date1}::date)"
+            else:
+                # For other units, fall back to extracting from interval
+                return f"EXTRACT({unit} FROM AGE({date2}, {date1}))::int"
+
+        expr = re.sub(
+            r"TIMESTAMPDIFF\s*\(\s*(\w+)\s*,\s*(.+?)\s*,\s*(.+?)\s*\)",
+            replace_timestampdiff,
+            expr,
+            flags=re.IGNORECASE,
+        )
+
+        # CURDATE() → CURRENT_DATE
+        expr = re.sub(r"CURDATE\s*\(\s*\)", "CURRENT_DATE", expr, flags=re.IGNORECASE)
+
+        # NOW() → CURRENT_TIMESTAMP (already works but ensure compatibility)
+        expr = re.sub(r"\bNOW\s*\(\s*\)", "CURRENT_TIMESTAMP", expr, flags=re.IGNORECASE)
+
         return expr
 
     # =========================================================================

src/datajoint/diagram.py

@@ -134,7 +134,8 @@ def __init__(self, source, context=None) -> None:
                     except AttributeError:
                         raise DataJointError("Cannot plot Diagram for %s" % repr(source))
                 for node in self:
-                    if node.startswith("`%s`" % database):
+                    # Handle both MySQL backticks and PostgreSQL double quotes
+                    if node.startswith("`%s`" % database) or node.startswith('"%s"' % database):
                         self.nodes_to_show.add(node)
 
         @classmethod

src/datajoint/heading.py

@@ -572,11 +572,12 @@ def _init_from_database(self) -> None:
                 nullable=nullable,
             )
         self.indexes = {
-            tuple(item[k]["column"] for k in sorted(item.keys())): dict(
+            tuple(item[k]["column"] for k in sorted(item.keys()) if item[k]["column"] is not None): dict(
                 unique=item[1]["unique"],
                 nullable=any(v["nullable"] for v in item.values()),
             )
             for item in keys.values()
+            if any(item[k]["column"] is not None for k in item.keys())
         }
 
     def select(self, select_list, rename_map=None, compute_map=None):

src/datajoint/table.py

@@ -1143,7 +1143,7 @@ def describe(self, context=None, printout=False):
         definition = "# " + self.heading.table_status["comment"] + "\n" if self.heading.table_status["comment"] else ""
         attributes_thus_far = set()
         attributes_declared = set()
-        indexes = self.heading.indexes.copy()
+        indexes = self.heading.indexes.copy() if self.heading.indexes else {}
         for attr in self.heading.attributes.values():
             if in_key and not attr.in_key:
                 definition += "---\n"