Menu
If I create table with primary key is index automatically created for the table or does that need doing separately.
i.e if this is the table ddl
CREATE TABLE release(guid varchar(36) NOT NULL PRIMARY KEY, name varchar(255),xmldata CLOB(512 K)) do I also need to do
CREATE INDEX release_idx ON release(guid) or not
(I'm using Derby a database that comes with Java)
372
In MySQL, a primary index is automatically created, and we have already described above how MySQL chooses the primary index. But in the database world, it's actually not necessary to create an index on the primary key column — the primary index can be created on any non primary key column as well.
Yes, primary key is automatically indexed in MySQL because primary key, index, etc gets stored into B-trees. All engines including InnoDB as well as MyISAM automatically supports the primary key to be indexed. The primary key is implicitly indexed in InnoDB, MyISAM, and other engines.
A primary index is automatically created for the primary key and ensures that the primary key is unique. You can use the primary index to retrieve and access objects from the database. The unique index is a column, or an ordered collection of columns, for which each value identifies a unique row.
When you create a PRIMARY KEY constraint, a unique clustered index on the column or columns is automatically created if a clustered index on the table does not already exist and you do not specify a unique nonclustered index. The primary key column cannot allow NULL values.
You don't need to. The primary key is already an index.
161
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
