fix(sql-parser): prevent bad urns from alter table lineage

metadata-ingestion/src/datahub/sql_parsing/sqlglot_lineage.py

@@ -197,6 +197,7 @@ def _table_level_lineage(
             sqlglot.exp.Update,
             sqlglot.exp.Delete,
             sqlglot.exp.Merge,
+            sqlglot.exp.AlterTable,
         )
         # In some cases like "MERGE ... then INSERT (col1, col2) VALUES (col1, col2)",
         # the `this` on the INSERT part isn't a table.
@@ -218,6 +219,7 @@ def _table_level_lineage(
         {
             _TableName.from_sqlglot_table(table)
             for table in statement.find_all(sqlglot.exp.Table)
+            if not isinstance(table.parent, sqlglot.exp.Drop)
         }
         # ignore references created in this query
         - modified

metadata-ingestion/tests/unit/sql_parsing/goldens/test_bigquery_alter_table_column.json

@@ -0,0 +1,14 @@
+{
+    "query_type": "UNKNOWN",
+    "query_type_props": {},
+    "query_fingerprint": "7d04253c3add0194c557942ef9b7485f38e68762d300dad364b9cec8656035b3",
+    "in_tables": [],
+    "out_tables": [
+        "urn:li:dataset:(urn:li:dataPlatform:bigquery,my-bq-project.covid_data.covid_deaths,PROD)"
+    ],
+    "column_lineage": null,
+    "debug_info": {
+        "confidence": 0.2,
+        "generalized_statement": "ALTER TABLE `my-bq-project.covid_data.covid_deaths` DROP COLUMN patient_name"
+    }
+}

metadata-ingestion/tests/unit/sql_parsing/test_sqlglot_lineage.py

@@ -1202,3 +1202,13 @@ def test_bigquery_information_schema_query() -> None:
         dialect="bigquery",
         expected_file=RESOURCE_DIR / "test_bigquery_information_schema_query.json",
     )
+
+
+def test_bigquery_alter_table_column() -> None:
+    assert_sql_result(
+        """\
+ALTER TABLE `my-bq-project.covid_data.covid_deaths` drop COLUMN patient_name
+    """,
+        dialect="bigquery",
+        expected_file=RESOURCE_DIR / "test_bigquery_alter_table_column.json",
+    )