The NDB storage engine, on the other hand, requires an explicit unique key (or primary key) on any column referenced as a foreign key. The handling of foreign key references to nonunique keys or keys that contain NULL values is not well defined for operations such as UPDATE or DELETE ...
( id bigint auto_increment primary key, created_at datetime not null, updated_at datetime not null, deleted_at datetime null, seller_id varchar(50) not null, region varchar(2) not null, app_id bigint null, constraint seller_app_sellers foreign key (app_id) references app (app_id) on...
The docs say "The handling of foreign key references to nonunique keys or keys that contain NULL values is not well defined ... You are advised to use foreign keys that reference only UNIQUE (including PRIMARY) and NOT NULL keys." Good advice, as you've found.Navigate...
The UK_TestDimB_TestDimAID is another unique key created upon the TestDimAID.Many cases can use similar code as this sample, but if the requirement is to create foreign key on non-primary key, or multiple-column keys, the code will look different. Details will be shown in next lesson....
A primary key can't exceed 16 columns and a total key length of 900 bytes. The index generated by a primary key constraint can't cause the number of indexes on the table to exceed 999 nonclustered indexes and 1 clustered index.
CREATE FOREIGN TABLE ft_region ( R_REGIONKEY int, R_NAME TEXT, R_COMMENT TEXT , primary key (R_REGIONKEY) not enforced) SERVER hdfs_server OPTIONS(format 'orc', encoding 'utf8', foldername '/user/hive/warehouse/gauss.db/region_orc11_64stripe') DISTRIBUTE BY roundrobin; Check whether...
Let's see an example. We will create anauthortable and abooktable. Both tables have a primary key calledid.bookalso has a foreign key composed by a field calledauthor_id, which refers to theauthorprimary key. The foreign key constraint name is optional, but we'll specify it because we ...
Create foreign key relationships in SQL Server by using SQL Server Management Studio or Transact-SQL.
However, if the update rule is NO ACTION, parent unique keys can be updated as long as every child has a parent key by the time the update statement completes. A non-null update value of a foreign key must be equal to a value of the primary key of the parent table of the ...
in Access. Thank you for your help.How to repeat:In MySQL I take any of my tables with a text field in the primary key. I paste the 3dots character somewhere in this field. In Access, the table line immediately displays #deleted.Suggested fix:Allow special characters in primary keys. ...