php mysql query for updating a field

[sciwaysoft]

i want to change the data in the field 'subid' from x to d where the value of field autonum=4. and what will be the code to modify the null record.

My Table Structure

| autonum | subid |

| 1 | a |
| 2 | b |
| 3 | c |
| 4 | x |
| 5 | e |
| 6 | Null |

[LordShryku]

Basic syntax. RTFM

[Feffik]

update table set subid=d where subid=x