Setting value for one column of all records in table

Solution 1:

UPDATE your_table SET likes = NULL

or if your likes column does not allow NULL:

UPDATE your_table SET likes = ''

Some SQL tools that are used for executing DB queries prevent updates on ALL records (queries without a where clause) by default. You can configure that and remove that savety setting or you can add a where clause that is true for all records and update all anyway like this:

UPDATE your_table 
SET likes = NULL
WHERE 1 = 1

If you compare with NULL then you also need the IS operator. Example:

UPDATE your_table 
SET likes = NULL
WHERE likes IS NOT NULL

because comparing NULL with the equal operator (=) returns UNKNOWN. But the IS operator can handle NULL.