What are the commonly used functions in MySQL?

MySQL common functions

1. Numeric functions

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

2. String functions

The underline is commonly used (get the number of bytes)

Additional: char_length characters (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

In order to add separator:

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

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

Downline SQL statement description: The first now() is used for comparison, interval 50 minute means pushing back 50 units, - 50 means pushing forward 50 units year(now()) to get the year; month (now()) takes the month; day(now()) takes the day; nour(now()) takes the time; minute(now()) takes the minute; second(now()) takes the second

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

Get the week:

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

5. Aggregation function

Collect multiple data to calculate a single data value

Usage:

select sum(heigth) from c1;

Get the number of records (number of rows) and filter out null values: count() If one row in row 14 is empty, then count() is row 13. Count() can be added with count(*), which is more accurate. Count(*) is generally used to count

to calculate the number of units of difference between two dates, 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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