MySQL detailed summary of commonly used functions

MySQL Common Functions

1. Numeric Functions

Additional: ceil(x) For example, if ceil(1.23) has a value of 2, it can be written as ceiling(x)

String functions

The dash is commonly used (to get the number of bytes)

Add: char_length character (query the last three digits of the name) For example: char_length(name)=3 can be written as:

select left(name,1) from c1;

3. Time function

Usage: select now();

4. System Function

To add a separator:

select concat_ws('#',name,tel,height) from xxb;

select (substr(Now(),1,4)-substr(age,1,4) as agefrom zxc;

Explanation of the following SQL statements: The first now() is used for comparison, interval 50 minute means pushing back 50 units, and -50 means pushing forward 50 units. year(now()) gets the year; month(now()) gets the month; day(now()) gets the day; nour(now()) gets the hour; minute(now()) gets the minute; second(now()) gets the second

select now(),date_add(now(),interval 50 minute);  

Get the day of the week:

select dayofweek(now()),dayname(now());

5. Aggregation Functions

Aggregate multiple data to calculate a single data value

usage:

select sum(height) from c1;

Get the number of records (number of rows), and filter out empty values: count() If there is one empty row in 14 rows, count() will be 13 rows. Count() can be accompanied by count(*) for more accuracy. Count(*) is generally used for statistics.

Calculate the difference between two dates in multiple units, such as: select timestampdiff (time unit, date time 1, date time 2) written as:

select timestampdiff(day,'2021-11-18','2021-11-22');

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