So far, we've discussed that the data in a table can form relationships to other tables (for example, one-to-one, one-to-many). However, it has not occurred to us that the
data columns in the table themselves are related to other columns. Understanding this layer of relationship is the key to understanding the second and third paradigms.
when the data of a column must change with the data of another column, the first column
function depends on the second column.
basically reading from right to left is the way to interpret dependencies.
Partial function dependency: A partial function dependency refers to a column of a non-primary key that relies on a part of the combined primary key (but not entirely dependent on the combined primary key)
If you change any of the non-primary key columns, it is a
transitive dependency that may be changed by other columns.
the
first paradigm , also known as 1NF: Rule One: Data columns contain only
atomic values rule two: no
duplicate data groups
the
second Paradigm , also known as 2NF: rule one: conform to the first paradigm first; rule two: No partial function Dependencies
the
third paradigm , also known as 3NF: Rule one: 2NF compliant; Rule two: there is no
non-primary attribute dependency on any of the candidate key field's transfer functions
the
canonical Paradigm , also known as the BC Paradigm: Rule one: 3NF compliant; rule two: The primary attribute is not dependent on the primary attribute (that is, no
field exists for the transfer function dependency of any of the candidate key fields)
Classic
ACID detection: atomicity, every step in a transaction must be completed, otherwise it will not be completed. consistency, the consistency of the database should be maintained after the transaction is complete. After two sets of monetary transactions are completed, the amount of money should match the balance of the account. isolation, which means that each transaction will see a consistent database, regardless of what other transactions are doing. persistent, the database needs to properly store data and protect data from power outages or other threats when the transaction is complete.
Morning Tidy Database Basics points
