Three common strategies: Create a table for each class in the hierarchy that contain the properties defined for each class and a foreign key back to the top-level superclass table. So you might have a vehicle table with other tables like car and airplane that have a vehicle_id column. The disadvantage here is that you … Read more
Using Oracle you can setup a Trigger on a table and then have the trigger send a JMS message. Oracle has two different JMS implementations. You can then have a process that will ‘listen’ for the message using the JDBC Driver. I have used this method to push changes out to my application vs. polling. … Read more
Surrogate key, synthetic key and artificial key are synonyms. Technical key is another one. They all mean “primary key which doesn’t have a business meaning”. They are distinct from natural or business keys which have a meaning beyond the system at hand. For instance, consider the SO user account. We are identified by two keys. … Read more
Just allow column university_id of table user to allow NULL value so you can save nulls. CREATE TABLE user ( uid INT NOT NULL, Name VARCHAR(30) NOT NULL, university_ID INT NULL, — <<== this will allow field to accept NULL CONSTRAINT user_fk FOREIGN KEY (university_ID) REFERENCES university(university_ID) ) UPDATE 1 based on your comment, you … Read more
I’ve got to store DD/MM dates in a database, but I’m not sure of the best way to store this so that it can be easily sorted and searched. The best way to store date data, even if the year component is not required, is to use date. When you need to use it, you … Read more
Short answer to the title: No A bit longer answer: You should learn to use arrays when appropriate. Arrays are not bad design themselves, they are as atomic as a character varying field (array of characters, no?) and they exists to make our lives easier and our databases faster and lighter. There are issues considering … Read more
As a rule of thumb, indexes should be on any fields that you use in joins or where clauses (if they have enough different values to make using an index worthwhile, field with only a few possible values doesn’t benefit from an index which is why it is pointless to try to index a bit … Read more
show full columns from <table_name> This is the output: | Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment I hope this is useful for you
There is a catch in what you ask for: it all depends on your data. Fundamentally Redis is a data structure server. How you structure your data depends almost entirely on what it is and how you need to access it. The simple and common cases are fairly well covered by the links you list. … Read more