Sql insert ignore does not work because of timestamp now() - php

Question

I am trying to prevent duplicate entries like this
INSERT IGNORE INTO myTable( `val_1`, `val_2`, `val_3`, `date` )
VALUES ( '$var_1', '$var_2', '$var_3', now() )
The values i would like to check are the 3 val_x but because now() will be a unique value, insert ignore does not work.
How can i not check that last variable as unique?
note: this is kind of like a cart, so i cannot make the first 3 values unique. There is a session variable that allows each user to see a a unique collection.
From this diagram, the first 2 rows are duplicate since they belong to the same user session. The 3rd row is not a duplicate becase it belongs to a different user session
+---------+-------+--------+
| session | var 1 | var 2 |
+---------+-------+--------+
| abc1234 | aaaaa | bbbbb |
+---------+-------+--------+
| abc1234 | aaaaa | bbbbb |
+---------+-------+--------+
| 5678def | aaaaa | bbbbb |
+---------+-------+--------+
| 5678def | aaaaa | ccccc |
+---------+-------+--------+
as paqogomez suggested i removed now() from the query and altered the table but it looks like i need a primary key for insert ignore to work, but for my scenario i cant make these 3 columns unique
ERROR 1062: Duplicate entry 'aaaaa' for key 'var 1'

Answer 1

I would suggest moving the date into the default value of the column.
ALTER TABLE mytable CHANGE `date` `date` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
This way, you can still deal with the duplicates in the data in PHP. The alternative, as others have suggested would result in a database foreign key error if you attempted to insert a duplicate.
Then this sql would work and give the same result:
INSERT IGNORE INTO myTable( `val_1`, `val_2`, `val_3` )
VALUES ( '$var_1', '$var_2', '$var_3' )
EDIT:
You still need a unique index to make it work. See #Gordon's answer

Answer 2

Create a unique index on the first three columns:
create unique index myTable_session_val2_val3 on myTable(session, val_1, val_2);
This will guarantee that combinations of these three are unique, without taking into account any other columns.

Answer 3

You should probably define the UNIQUE keys for the combination of columns you don't want to be duplicated. So, don't specify column date as UNIQUE. Did you verify that? Define rest of three values as unique columns. It will probably work.