表中所有记录的一列的设置值

Question

I'm trying to clear one column for all records in my table. For example, if my table had three columns: id , comment , and likes - I would like to be able to clear the likes column.

+---+-------+-----+
|id |comment|likes|
+-----------------+
|1  |hi     |3    |
|2  |hello  |12   |
|3  |hey    |1    |
+---+-------+-----+

so that afterwards it would look like this:

+---+-------+-----+
|id |comment|likes|
+-----------------+
|1  |hi     |     |
|2  |hello  |     |
|3  |hey    |     |
+---+-------+-----+

I'm guessing I would have to use MySQL UPDATE to clear the likes value, but how do I iterate through all records and keep the id and comment fields the same?

I don't want to change each record manually.

Answer 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 .