One-to-one: Use a foreign key to the referenced table: student: student_id, first_name, last_name, address_id address: address_id, address, city, zipcode, student_id # you can have a # “link back” if you need You must also put a unique constraint on the foreign key column (addess.student_id) to prevent multiple rows in the child table (address) from relating … Read more
Short answer: yes. Long answer: You need your table to be joinable on something If you want your table to be clustered, you need some kind of a primary key. If your table design does not need a primary key, rethink your design: most probably, you are missing something. Why keep identical records? In MySQL, … Read more
GUIDs may seem to be a natural choice for your primary key – and if you really must, you could probably argue to use it for the PRIMARY KEY of the table. What I’d strongly recommend not to do is use the GUID column as the clustering key, which SQL Server does by default, unless … Read more
In addition to violating First Normal Form because of the repeating group of values stored in a single column, comma-separated lists have a lot of other more practical problems: Can’t ensure that each value is the right data type: no way to prevent 1,2,3,banana,5 Can’t use foreign key constraints to link values to a lookup … Read more
A Table can have a Composite Primary Key which is a primary key made from two or more columns. For example: CREATE TABLE userdata ( userid INT, userdataid INT, info char(200), primary key (userid, userdataid) ); Update: Here is a link with a more detailed description of composite primary keys.
Basically it depends on the precision you need for your locations. Using DOUBLE you’ll have a 3.5nm precision. DECIMAL(8,6)/(9,6) goes down to 16cm. FLOAT is 1.7m… This very interesting table has a more complete list: http://mysql.rjweb.org/doc.php/latlng : Datatype Bytes Resolution Deg*100 (SMALLINT) 4 1570 m 1.0 mi Cities DECIMAL(4,2)/(5,2) 5 1570 m 1.0 mi Cities … Read more
1. Not using appropriate indices This is a relatively easy one but still it happens all the time. Foreign keys should have indexes on them. If you’re using a field in a WHERE you should (probably) have an index on it. Such indexes should often cover multiple columns based on the queries you need to … Read more
Lots of reads in every query, fewer regular writes Both databases perform well on reads where the hot data set fits in memory. Both also emphasize join-less data models (and encourage denormalization instead), and both provide indexes on documents or rows, although MongoDB’s indexes are currently more flexible. Cassandra’s storage engine provides constant-time writes no … Read more
Horizontal scaling means that you scale by adding more machines into your pool of resources whereas Vertical scaling means that you scale by adding more power (CPU, RAM) to an existing machine. An easy way to remember this is to think of a machine on a server rack, we add more machines across the horizontal … Read more
An identifying relationship is when the existence of a row in a child table depends on a row in a parent table. This may be confusing because it’s common practice these days to create a pseudokey for a child table, but not make the foreign key to the parent part of the child’s primary key. … Read more