Home/ Questions/Q 6191395
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-24T02:45:22+00:00

ALTER TABLE admins ADD CONSTRAINT uc_EmailandDeleted_at UNIQUE (email,deleted_at); I have changed my table to

  • 0
ALTER TABLE admins ADD CONSTRAINT uc_EmailandDeleted_at UNIQUE (email,deleted_at);

I have changed my table to work as this:

ID  EMAIL                  DELETED_AT  
1.  user@example.com          NULL             <- accept  
2.  user@example.com          NULL             <- reject because of uniqueness.

But Its not working as I wish. If i gave two identical dates to 

deleted_at

It is generating error as I expect. But not for NULL values. Any idea?

NB: I can’t change the behaviors of deleted_at column because I am using acts_as_paranoid. So I have to keep deleted_at field to be NULL or any date.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    From the documentation:

    A UNIQUE index creates a constraint such that all values in the index
    must be distinct. An error occurs if you try to add a new row with a
    key value that matches an existing row. This constraint does not apply
    to NULL values except for the BDB storage engine. For other engines, a
    UNIQUE index permits multiple NULL values for columns that can contain
    NULL.

    The above excerpt from MySQL 5.0. MySQL dropped the BDB storage engine in 5.1.12.
    So now from the latest documentation:

    For all engines, a UNIQUE index permits multiple NULL values for columns that can contain NULL. If you specify a prefix value for a column in a UNIQUE index, the column values must be unique within the prefix.

    • 0