MySQL summary data and mysql Summary

MySQL summary data and mysql Summary
Summary data sometimes operations on a data table are not the data itself, but the summary of the data in the table, such as the average, maximum, and minimum values of a column of data. MySQL provides functions for these commonly used data aggregation processes.
SQL Aggregate functions

Function	Description
COUNT ()	Returns the number of rows in a column.
MAX ()	Returns the maximum value of a column.
MIN ()	Returns the minimum value of a column.
AVG ()	Returns the average value of a column.
SUM ()	Returns the sum of values of a column.

Example:
The products table is shown as follows:


It looks strange to find the average value of the prod_price column. The original table only shows one row:

Obtain the prices of all commodities such as vend_id = 1003 for a specific row;

The COUNT function is used to determine the number of rows that meet certain conditions. There are 14 rows in the products table:

Count the number of rows in Vend_id = 1001:

MAX () Find the maximum value

MIN () Minimum

SUM () calculates the SUM of the values of the series.

Aggregate different values to calculate the number of vendors. With the DISTINCT keyword, only the number of different values in the column is counted:

Multiple Aggregate functions can be used together, with more powerful functions:



Mysql query Summary

First, the 40 records appended are not summarized.
This depends on whether the data you append is successful. In addition, you should check whether the data you append meets your query conditions. If all the data meets the requirements, then no problem will occur.

2. How to display statistics and summary results in the last line of output results
The union function can be used.
Select a unit number, B, c
Union
Select a unit number, count (*), sum (o pension)

It seems that this is because of the stop time field. In fact, this is a great change. What type of field is this field? Try it several times.
I don't know much about it.

Check if you have data on the stop time of the 40 data records. Is there any default value?
I guess it should be a null value.
So
The condition is changed to or q. The stop time is null.

How does mysql periodically Summarize data tables?

Use the SQL angent service of mssql to set a scheduled task and write the summary statement into the task.