SQL - Count

Data System Architecture


count in SQL count the number of row in a relation (table, query,…).

Database can use an index on a column to count the number of rows in the table only when the column has been declared NOT NULL

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Star Schema
Dimensional Data Modeling - Fact Table

A fact table is a table that stores fact where a fact can be seen as the representation of an event. It's also known as: Transactional history Unalterable fact. (The content of this kind of table...
Data System Architecture
Index - Performance

The impact of index on performance can be resumed as: Too many indexes and the performance of DML will suffer. Too few indexes and the performance of queries (including inserts, updates, and deletes)...
Data System Architecture
SQL - Null

NULL value in SQL represents missing data in SQL. NULL has its own data domain and implements therefore its own behavior. The most important one being that: An equality comparison of two NULL values...

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