# What is difference between aggregate functions: count and cumulative count?

The count is well known and is simple to explain. Count function counts a number of items/records that satisfy the given criteria.

The cumulative count function is the sum of all the counts generated so far. Mathematically it is represented as

Sk = âˆ‘Ci for i = 1 to k

When k = 3, i.e., 3rd cumulative count is calculated by adding up the first 3 counts C1, C2, C3

This might seem not very clear. So let's clear the air with an example:

Consider the following table:

Date | Count |
---|---|

5 | |

7 | |

2 | |

| 3 |

4 |

The above table is generated by using a simple count of specimens collected every day for the first 5 days of the month of Jan 2018. However, this table doesn't give an idea of how many specimens were collected in total until a given date. For this purpose, we need to use a cumulative count. The 3rd column in the below table is generated using the cumulative count function.

Date | Count | Cumulative Count |
---|---|---|

5 | 5 | |

7 | 12 | |

2 | 14 | |

3 | 17 | |

4 | 21 |

The difference can be best visualized using below the graph.