Unique constraint by 2 columns where one has a specific value
I have a problem with UNIQUE CONSTRAINT.
unique-constraint
How can I do ‘insert if not exists’ in MySQL?
I started by googling and found the article How to write INSERT if NOT EXISTS queries in standard SQL which talks about mutex tables.
Does MySQL ignore null values on unique constraints?
I have an email column that I want to be unique. But I also want it to accept null values. Can my database have 2 null emails that way?
MySQL – Make an existing Field Unique
I have an already existing table with a field that should be unique but is not. I only know this because an entry was made into the table that had the same value as another, already existing, entry and this caused problems.
MySQL: ALTER IGNORE TABLE gives “Integrity constraint violation”
I’m trying to remove duplicates from a MySQL table using ALTER IGNORE TABLE + an UNIQUE KEY. The MySQL documentation says:
SQL unique varchar case sensitivity question
I’m trying to populate a SQL table with a list of words. The table itself it pretty simple:
MySQL delete multiple rows in one query conditions unique to each row
So I know in MySQL it’s possible to insert multiple rows in one query like so:
Quickest way to check for pre-existing record before insert [mysql_errno()]
My question will use emails as an example, but this could apply to anything.
Unique constraint replaces existing foreign key
I have two tables, parent and child, the child table has a FK on the parent table using the parent_id column. When adding this FK I can see that the child table has both the FK and an index to represent that FK.