Does redis provide users to create data integrity or constraint? Like giving primary keys and foreign keys in sql. I can't seem to find it in the user manual. Thanks!
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I have come to know that primary and foreign keys are introduced to Hive tables. Is it possible to achieve delete cascade functionality for the rows through Hive QL?
Can anyone help me in understanding the reason and uses of implementing key constraints in Hive (as the constraints are not imposed on table data directly)? Also please help me in understanding the possibility to achieve delete cascade functionality through Hive Schema and HiveQL without coding
These constraints can be only in DISABLE state, meaning that all incoming data is not checked:
PRIMARY KEY
FOREIGN KEY
UNIQUE KEY
These constraints in Hive are not backed by indexes like it is in RDBMS and NO CASCADE operations supported.
The purpose of having disabled constraints is to
provide information to CBO (RELY | NORELY) to make it possible to make smart optimizations
provide information to modelling tools like ERWin
document what is supposed to be PK, UK, FK
I recently created a relational database model and it has a lot of primary key and foreign key relations. I want to use clickhouse for my database but it turns out that clickhouse does not support foreign key and unique primary keys. Can someone tell me if I am missing anything here.
You are right. CH does not have unique & foreign constraints.
Moreover JOINs are not the best part of ClickHouse.
ClickHouse suggests to create single wide denormalized table and avoid joins as possible.
I am currently using PopSQL for my school project. Can someone help me with this problem?
The error message is self-explanatory. You need an index on the column that the foreign key refers to.
So, do create it:
create index idx_section_sectno on section(sectno):
Also, you might want to read the MySQL documentation for foreign key constraints:
MySQL requires indexes on foreign keys and referenced keys so that foreign key checks can be fast and not require a table scan.
Other conditions apply to forein keys that you want to be aware of.
Is it possible to have both foreign key constraint and a trigger that keep the referential integrity?
I don't think that is possible and we have to remove the constraint and keep the referential integrity using trigger. To extend my description, suppose you have two tables one of them has a primary key and the other has a foreign key referring to the first table, primary key column. So now is it possible to add the following code
create or replace TRIGGER TABLE1_TABLE2
after update of TABLE1_PRIMARY_KEY on TABLE1
Of course it came to my mind to lose the constraint and continue with the trigger but is it the only way?
By the way this code is just for practice, I know it isn't a good idea to update the primary key of a table.
I found a useful article on one of Microsoft websites confirming my idea that the constraints should be removed. But of course the solution for Oracle may be different from any other database. The article is about Implementing Referential Integrity and Cascading Actions and the part that is related is "Implementing ON DELETE CASCADE and ON UPDATE CASCADE with triggers" and after that comes "Before continuing, you need to drop the existing foreign keys".
There is no problem doing that in Oracle. You could have both the constraint and the trigger at the same time.
I have a table which is to be replicated using Transactional Replication.
This table has a composite primary key . These are a combination of varchar and numeric columns.
I want to understand if this table can be replicated with a composite primary key?
Please let me know.
Thanks in advance.
Yes, this table can be replicated with a composite primary key. Just keep in mind with Transactional Replication there must be a declared primary key for the published table.
Considerations for Transactional Replication