MySQL common/common functions

Table of contents

date function

string functions

math function

other functions

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date function

Get hours, minutes and seconds:

select current_time();

+----------------+

| current_time() |

+----------------+

| 13 :51:21 |

+----------------+

date is date

Get the timestamp:

select current_timestamp();

+---------------------+

| current_timestamp() |

+---------------------+

| 2017 - 11 - 19 13 :51:48 |

+---------------------+

string functions

length returns bytes.

Get the character set of the ename column of the emp table

select charset(ename) from EMP;

It is required to display the information in the exam_result table, and the display format is: "XXX has XXX points for Chinese , XXX points for mathematics, and XXX points for English "

select concat(name, ' Chinese is ' ,chinese, ' fen, mathematics is ' ,math, ' fen ' ) as ' score ' from student;

Find the number of bytes occupied by the student name in the student table

select length(name), name from student;

Note: The length function returns the length of the string in bytes. If it is a multibyte character, calculate the number of bytes;

Single-byte characters count as one byte. For example: letters and numbers are counted as one byte, and Chinese means multiple bytes

(related to character set encoding)

Replace all names with S in the EMP table with ' Shanghai '

select replace(ename, 'S', '上海') ,ename from EMP;

Intercept the second to third characters of the ename field in the EMP table

select substring(ename, 2, 2), ename from EMP;

Display all employee names in lowercase

select concat(lcase(substring(ename, 1, 1)),substring(ename,2)) from EMP;  

math function

absolute value

select abs(-100.2);

Rounded up

select ceiling(23.04);

round down

select floor(23.7);

Keep 2 decimal places (decimals are rounded )

select format(12.3456, 2);

Generate random numbers

select rand();  

other functions

user() queries the current user

select user();

md5(str) performs an md5 digest on a string, and obtains a 32- bit string after the digest

select md5( 'admin' )

+----------------------------------+

| md5( 'admin' ) |

+----------------------------------+

| 21232 f297a57a5a743894a0e4a801fc3 |

+----------------------------------+

database() displays the database currently in use

select database();

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

select password( 'root' );

+-------------------------------------------+

| password( 'root' ) |

+-------------------------------------------+

| * 81 F5E21E35407D884A6CD4A731AEBFB6AF209E1B |

+-------------------------------------------+

ifnull ( val1 , val2 ) returns val2 if val1 is null , otherwise returns the value of val1

select ifnull( 'abc' , '123' );

+----------------------+

| ifnull( 'abc' , '123' ) |

+----------------------+

| abc |

+----------------------+

1 row in set ( 0.01 sec)

select ifnull( null , '123' );

+---------------------+

| ifnull( null , '123' ) |

+---------------------+

| 123 |

+---------------------+

1 row in set ( 0.00 sec)