In most cases . . . “Staff” always describes people. Some customers are people. Some customers are businesses (organizations). “Suppliers” are usually (always?) organizations. Staff can also be customers. Suppliers can also be customers. There are serious problems with having separate tables of staff phone numbers, supplier phone numbers, and customer phone numbers. Staff can … Read more
The term “repeating group” originally meant the concept in CODASYL and COBOL based languages where a single field could contain an array of repeating values. When E.F.Codd described his First Normal Form that was what he meant by a repeating group. The concept does not exist in any modern relational or SQL-based DBMS. The term … Read more
1NF is the most basic of normal forms – each cell in a table must contain only one piece of information, and there can be no duplicate rows. 2NF and 3NF are all about being dependent on the primary key. Recall that a primary key can be made up of multiple columns. As Chris said … Read more
SQL treats NULL specially per its version of 3VL (3-valued logic). Normalization & other relational theory does not. However, we can translate SQL designs into relational designs and back. (Assume no duplicate rows here.) Normalization happens to relations and is defined in terms of operators that don’t treat NULL specially. The term “normalization” has two … Read more
I try to attempt to explain normalization in layman terms here. First off, it is something that applies to relational database (Oracle, Access, MySQL) so it is not only for MySQL. Normalisation is about making sure each table has the only minimal fields and to get rid of dependencies. Imagine you have an employee record, … Read more
We need to know all the FDs (functional dependencies) that hold to determine CKs (candidate keys), not just those in some list. Look at a (correct & general) definition of CK or algorithm for finding CKs (in a published textbook, not a youtube video). Is your list appropriately a closure (all the FDs that hold) … Read more
Normalization is basically to design a database schema such that duplicate and redundant data is avoided. If the same information is repeated in multiple places in the database, there is the risk that it is updated in one place but not the other, leading to data corruption. There is a number of normalization levels from … Read more
A relation has an associated set of columns of any type and an associated set of rows. There is one value per column per row. Sometimes “normalize” is used to mean (1) “decompose each relation to smaller relations that are its projections and that join back to it”. This is normalization to higher NFs (normal … 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