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Mysql automatically updating foreign keys
I was dumbfounded to learn about My SQL’s sql-mode option. That means My SQL changes the column value each time you update the row.What My SQL developer ever thought that this was a good default behavior?If no clustered index is defined on the table, SQL Server creates a clustered index; otherwise, a nonclustered index is created.
First, we need to create a simple table for Authors.
There are only two columns: a primary key and the author's name Next, we create a simple table for Books.
Maybe with the first-class replication in the 9.0 release, it will happen sooner rather than later.
The default storage engine in My SQL (My ISAM) does not support Foreign Key constraints.
This makes deployments a crap shoot–whether you’re using migrations or a hand-coded SQL upgrade script, you better hope the whole thing applies cleanly, because if your script blows up halfway through, you’re stuck with a schema that is somewhere between versions.
Getting back to a deployable state, or even one where you can rerun the fixed upgrade script, means either manually teasing the schema back to the old version, or reverting to a snapshot and starting all over.My SQL still doesn’t have deferred foreign key constraints, Postgre SQL has had them for as long as I’ve used it. Deferred unique constraints are similar, but mean you can temporarily violate a unique constraint, as long as you clean things up before the transaction commits.E.g.: to the new value, and have your ORM auto-flush. My SQL doesn’t have deferred unique constraints, Postgre SQL just got them in (the nearly released) 9.0.For example, a primary key is often made up of a single column.Regardless of how many values are repeated in other columns, the primary key values are always unique and consequently ensure that each row can be identified separately from all other rows.In addition, if you create a composite primary key (more than one column), the individual columns can contain duplicate values, but the columns collectively cannot and together must provide the unique identifiers for each row.For example, the table When you create a primary key, SQL Server automatically creates an index based on the key columns.And this isn’t just My ISAM–this is the Inno DB engine as well.Postgre SQL, on the other hand, executes all DDL within a real transaction, and if one , and doing a final flush commit.If you want to use Foreign Keys in Mysql, you need to use Inno DB.The following is a simple example that illustrates Foreign Key constraints, we'll create tables to store information about Authors and their Books. Note, that in My SQL we need to use the Inno DB storage engine to support Foreign Key Constraints.