Add example script to extract column names.

examples/extract_column_names.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2009-2020 the sqlparse authors and contributors
+# <see AUTHORS file>
+#
+# This example is part of python-sqlparse and is released under
+# the BSD License: https://opensource.org/licenses/BSD-3-Clause
+#
+# This example illustrates how to extract table names from nested
+# SELECT statements.
+#
+# See:
+# https://groups.google.com/forum/#!forum/sqlparse/browse_thread/thread/b0bd9a022e9d4895
+
+import sqlparse
+from sqlparse.sql import IdentifierList, Identifier
+from sqlparse.tokens import Keyword, DML
+
+
+def extract_select_part(parsed):
+    select_seen = False
+    for item in parsed.tokens:
+        if item.ttype is Keyword and item.value.upper() == 'FROM':
+            return
+        if select_seen:
+            yield item
+        if item.ttype is DML and item.value.upper() == 'SELECT':
+            select_seen = True
+
+
+def extract_column_identifiers(token_stream):
+    for item in token_stream:
+        if isinstance(item, IdentifierList):
+            for identifier in item.get_identifiers():
+                yield identifier.get_name()
+        elif isinstance(item, Identifier):
+            yield item.get_name()
+
+
+def extract_columns(sql):
+    stream = extract_select_part(sqlparse.parse(sql)[0])
+    return list(extract_column_identifiers(stream))
+
+
+if __name__ == '__main__':
+    sql = """
+    WITH schema AS (
+        SELECT a, b, c, d
+        FROM schema
+    )
+    SELECT ALL t0_as_b, `t1_as_c` AS "t1 as c", COUNT(*) AS "count"
+    FROM (
+        SELECT ALL `t0_as_b`, max(`t1_as_c`) AS `t1_as_c`, max(`t2 d as d`) AS `t2 d as d`
+        FROM (
+            SELECT a, b AS `t0_as_b`
+            FROM schema
+        ) t0
+            INNER JOIN (
+                SELECT a, c AS "t1_as_c"
+                FROM schema
+            ) t1
+            ON t0.a = t1.a
+            INNER JOIN (
+                SELECT a, d AS 't2 d as d'
+                FROM schema
+            ) t2
+            ON t0.a = t2.a
+        WHERE 1 = 1
+        GROUP BY a, `t0_as_b`
+    ) "virtual_table"
+    GROUP BY `t0_as_b`, `t1_as_c`
+    ORDER BY `t1_as_c` DESC
+    LIMIT 1000;
+    """
+
+    columns = ', '.join(extract_columns(sql))
+    print('Columns: {}'.format(columns))
+    # >>> [Output]:
+    # >>> Columns: t0_as_b, t1 as c, count