MySQL built-in functions

Date function

1. Get date

2. Obtain hours, minutes and seconds ：

3. Get timestamp

4. Add a date to the date

5. Subtract the time from the date

6. Calculate the number of days between two dates

Use example 1

Create a table to record birthdays

Add a date to the table

Use example 2

Create a message table

Show all message messages , The release date only shows the date , Don't show the time ; Query information sent within a specified time

String function

1. charset

2. concat

3. instr

4. ucase and lcase

5. left

6. length

7. replace

8. strcmp

9. substring

10. ltrim rtrim trim

Use example 1

Ask to show student Information in the table , Display format ：“XXX My language is XXX branch , mathematics XXX branch , English XXX branch ”

Use example 2

Find the number of bytes occupied by students' names in the student table

Be careful ： length Function returns the length of the string , In bytes . If it is a multi byte character, calculate the number of bytes ; If it is a single byte character, it is counted as a byte . such as ： Letter , The array counts as a byte , Chinese means multiple bytes （ Related to character set encoding ）

Use example 3

take EMP There are... In all the names in the table S Of is replaced by ’ - ’

Use example 4

Intercept EMP In the table ename The second to third characters of the field

Use example 5

Display the names of all employees in capital letters

Mathematical functions

1. The absolute value

2. Hexadecimal conversion

3. integer

4. Generate random numbers

Other functions

1. user() Query current user

2. md5(str) To a string md5 Abstract , After the summary, we get a 32 A string

md5（stri） It is often used in password encryption , The process is as follows

3. database() Displays the database currently in use

4. password() function ,MySQL The database uses this function to encrypt users

5. ifnull（val1, val2） If val1 by null, return val2, Otherwise return to val1 Value