Confused about nested tables in Oracle SQL

Question

I have attached the image with the SQL queries which are mentioned in Oracle documentation of Nested Tables and how to access the entries from the tables. But I cannot understand the SELECT statements used in there. Can someone explain me the actual meaning of the SELECT query used in there?Screenshot of Oracle SQL documentation on Nested Tables

Create a table with NESTED TABLE column,

CREATE OR REPLACE TYPE my_tab_t AS TABLE OF VARCHAR2(30);
/
CREATE TABLE nested_table (id NUMBER, col1 my_tab_t)
NESTED TABLE col1 STORE AS col1_tab;

Insert data into table,

INSERT INTO nested_table VALUES (1, my_tab_t('A'));
INSERT INTO nested_table VALUES (2, my_tab_t('B', 'C'));
INSERT INTO nested_table VALUES (3, my_tab_t('D', 'E', 'F'));
COMMIT;

The SQL query that I couldn't get,

SELECT id, COLUMN_VALUE FROM nested_table t1, TABLE(t1.col1) t2;

The result is displayed as,

    ID COLUMN_VALUE

---

     1 A
     2 B
     2 C
     3 D
     3 E
     3 F

6 rows selected.

Answer 1

Syntax FROM nested_table t1, TABLE(t1.col1) t2 is the old Oracle syntax for a CROSS JOIN, you should not use it nowadays. Better write

FROM nested_table t1 
   CROSS JOIN TABLE(t1.col1) t2

CROSS JOIN means, you combine each row from t1 with each row from t2. You should find many explanations in the internet.