feat: add build_table_metrics_query method for enhanced column metrics

dcs_core/integrations/databases/postgres.py

@@ -12,7 +12,10 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 
+import datetime
+from decimal import Decimal
 from typing import Any, Dict, List, Optional, Tuple
+from uuid import UUID
 
 from sqlalchemy import create_engine, text
 from sqlalchemy.engine import URL
@@ -309,3 +312,102 @@ def fetch_sample_values_from_database(
         result = self.connection.execute(text(query))
         rows = result.fetchall()
         return rows
+
+    def build_table_metrics_query(
+        self,
+        table_name: str,
+        column_info: list[dict],
+        additional_queries: Optional[List[str]] = None,
+    ) -> list[dict]:
+        query_parts = []
+        if not column_info:
+            return []
+
+        for col in column_info:
+            name = col["column_name"]
+            dtype = col["data_type"].lower()
+
+            query_parts.append(
+                f'COUNT(DISTINCT {self.quote_column(name)}) AS "{name}_distinct"'
+            )
+            query_parts.append(
+                f'COUNT(*) - COUNT(DISTINCT {self.quote_column(name)}) AS "{name}_duplicate"'
+            )
+            query_parts.append(
+                f'SUM(CASE WHEN {self.quote_column(name)} IS NULL THEN 1 ELSE 0 END) AS "{name}_is_null"'
+            )
+
+            if dtype in (
+                "int",
+                "integer",
+                "bigint",
+                "smallint",
+                "decimal",
+                "numeric",
+                "float",
+                "double",
+            ):
+                query_parts.append(f'MIN({self.quote_column(name)}) AS "{name}_min"')
+                query_parts.append(f'MAX({self.quote_column(name)}) AS "{name}_max"')
+                query_parts.append(
+                    f'AVG({self.quote_column(name)}) AS "{name}_average"'
+                )
+
+            elif dtype in ("varchar", "text", "char", "string", "character varying"):
+                query_parts.append(
+                    f'MAX(CHAR_LENGTH({self.quote_column(name)})) AS "{name}_max_character_length"'
+                )
+
+        if additional_queries:
+            for queries in additional_queries:
+                query_parts.append(queries)
+
+        qualified_table = self.qualified_table_name(table_name)
+        query = f'SELECT\n    {",\n    ".join(query_parts)}\nFROM {qualified_table};'
+
+        result = self.connection.execute(text(query))
+        row = dict(list(result)[0]._mapping)
+
+        def _normalize_metrics(value):
+            """
+            Safely normalizes DB metric values into JSON-serializable Python types.
+            Handles:
+            - Decimal → float
+            - datetime/date → ISO 8601 string
+            - UUID → string
+            - Nested dict/list recursion
+            - None passthrough
+            """
+            if value is None:
+                return None
+
+            if isinstance(value, Decimal):
+                return float(value)
+            if isinstance(value, (int, float, bool)):
+                return value
+
+            if isinstance(value, (datetime.datetime, datetime.date)):
+                return value.isoformat()
+
+            if isinstance(value, UUID):
+                return str(value)
+
+            if isinstance(value, list):
+                return [_normalize_metrics(v) for v in value]
+            if isinstance(value, dict):
+                return {k: _normalize_metrics(v) for k, v in value.items()}
+
+            return str(value)
+
+        column_wise = []
+        for col in column_info:
+            name = col["column_name"]
+            col_metrics = {}
+
+            for key, value in row.items():
+                if key.startswith(f"{name}_"):
+                    metric_name = key[len(name) + 1 :]
+                    col_metrics[metric_name] = _normalize_metrics(value)
+
+            column_wise.append({"column_name": name, "metrics": col_metrics})
+        return column_wise