Question

I have a table

id | col1 | col3| col4
1  | x    |  r  |
2  | y    |  m  |
3  | z    |  p  |
4  | x    |  r  |

i have to update all unique rows of this table
i.e

  id | col1 | col3| col4
  1  | x    |  r  |  1
  2  | y    |  m  |  1
  3  | z    |  p  |  1
  4  | x    |  r  |  0

i can fetch unique rows by

  select distinct col1,col2 from table

.But how can i identify these rows in order to update them.Please help.

Answer 1

You can use the group by to pick unique result:

SELECT MIN(ID) AS ID FROM TABLE GROUP BY COL1, COL3;

  id | col1 | col3
  1  | x    |  r  
  2  | y    |  m  
  3  | z    |  p  

Then

UPDATE TABLE SET col4 = 1 WHERE ID IN (SELECT MIN(ID) FROM TABLE GROUP BY COL1, COL3);

Restriction is that the id column should be unique.