New way of deriving named parameters using explain, refs #1421

datasette/utils/__init__.py

@@ -1076,3 +1076,15 @@ class PrefixedUrlString(str):
 
 class StartupError(Exception):
     pass
+
+
+_re_named_parameter = re.compile(":([a-zA-Z0-9_]+)")
+
+async def derive_named_parameters(db, sql):
+    explain = 'explain {}'.format(sql.strip().rstrip(";"))
+    possible_params = _re_named_parameter.findall(sql)
+    try:
+        results = await db.execute(explain, {p: None for p in possible_params})
+        return [row["p4"].lstrip(":") for row in results if row["opcode"] == "Variable"]
+    except sqlite3.DatabaseError:
+        return []