How can I Update the table so that....

Question

I have a table XYZ with values like
x y
1 null
1 null
1 null
1 null
2 null
2 null
3 null
4 null
4 null
4 null
I want to update my table so that the values for column y appears the serial no for the given x. The output would be like
x y
1 1
1 2
1 3
1 4
2 1
2 2
3 3
4 1
4 2
4 3
How can I write the Update statement?

Answer 1

SQL> CREATE TABLE t (x INTEGER, y INTEGER)
Table created.
SQL> INSERT INTO t
     VALUES (1, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (1, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (1, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (1, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (2, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (2, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (3, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (4, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (4, NULL)
1 row created.
SQL> INSERT INTO t
     VALUES (4, NULL)
1 row created.
SQL> UPDATE t t1
   SET y =
          (SELECT l
             FROM (SELECT ROWID rid,
                          ROW_NUMBER () OVER (PARTITION BY x ORDER BY NULL) l
                     FROM t t2)
            WHERE t1.ROWID = rid)
10 rows updated.
SQL> SELECT *
  FROM t
         X          Y
         1          1
         1          2
         1          3
         1          4
         2          1
         2          2
         3          1
         4          1
         4          2
         4          3
10 rows selected.