Normalization in database design is a process that organizes data to reduce redundancy and improve data integrity. Here are three common normalization rules, each corresponding to a specific normal form:
1. First Normal Form (1NF):
- Description: A table is in the first normal form if it contains only atomic (indivisible) values and each record within the table is unique. This means that each column of the table must hold only one value per row, with no repeating groups or arrays. Ensuring data is in 1NF is fundamental in avoiding duplicate and inconsistent data.
2. Second Normal Form (2NF):
- Description: A table is in second normal form if it is in first normal form and all non-key attributes are fully functional dependent on the primary key. This means that all columns in the table that are not part of the primary key must depend on the entire primary key for their values, not just a part of it. 2NF helps to further reduce redundancy by ensuring that each piece of data is stored only once and that it is stored in a table with other data to which it is directly related.
3. Third Normal Form (3NF):
- Description: A table is in third normal form if it is in second normal form and all its columns are not only fully dependent on the primary key, but also independent of each other. In other words, no column value should depend on another non-primary key column value. This eliminates transitive dependencies (where one non-key column's value depends on another non-key column's value), thereby further increasing data integrity and reducing redundancy.
1. First Normal Form (1NF):
- Description: A table is in the first normal form if it contains only atomic (indivisible) values and each record within the table is unique. This means that each column of the table must hold only one value per row, with no repeating groups or arrays. Ensuring data is in 1NF is fundamental in avoiding duplicate and inconsistent data.
2. Second Normal Form (2NF):
- Description: A table is in second normal form if it is in first normal form and all non-key attributes are fully functional dependent on the primary key. This means that all columns in the table that are not part of the primary key must depend on the entire primary key for their values, not just a part of it. 2NF helps to further reduce redundancy by ensuring that each piece of data is stored only once and that it is stored in a table with other data to which it is directly related.
3. Third Normal Form (3NF):
- Description: A table is in third normal form if it is in second normal form and all its columns are not only fully dependent on the primary key, but also independent of each other. In other words, no column value should depend on another non-primary key column value. This eliminates transitive dependencies (where one non-key column's value depends on another non-key column's value), thereby further increasing data integrity and reducing redundancy.
Forwarded from Diary of Boogey⚡️
Window functions are used расчет аггрегатов без группировки
Forwarded from Diary of Boogey⚡️
ЦПТ является одним из самых важных понятий в статистике. Она утверждает, что если взять достаточно большое количество выборок из любой популяции, средние значения этих выборок будут распределены нормально, независимо от формы исходного распределения популяции. Это предполагает, что:
1. Применение к любым данным: Даже если исходные данные не распределены нормально, средние значения множества выборок из этих данных будут следовать нормальному распределению.
1. Применение к любым данным: Даже если исходные данные не распределены нормально, средние значения множества выборок из этих данных будут следовать нормальному распределению.