examdb=# \d sample Table "test4.sample"

examdb=# \d sample
                      Table "test4.sample"
 Column |         Type          | Collation | Nullable | Default 
--------+-----------------------+-----------+----------+---------
 id     | integer               |           |          | 
 name   | character varying(10) |           |          | 
 tel    | character(11)         |           |          | 

examdb=# SELECT * FROM sample;
 id |  name  |     tel     
----+--------+-------------
  1 | SATO   | 09011111111
  2 | toda   | 09022222222
  3 | sato   | 09033333333
  4 | TODA   | 09044444444
  5 | TANAKA | 09055555555
(5 rows)

examdb=# UPDATE sample SET tel = NULL WHERE name !~* 'TO';
UPDATE 1

examdb=# SELECT * FROM sample;
 id |  name  |     tel     
----+--------+-------------
  1 | SATO   | 09011111111
  2 | toda   | 09022222222
  3 | sato   | 09033333333
  4 | TODA   | 09044444444
  5 | TANAKA | 
(5 rows)