【MySQL 09】Commonly used functions-Mysql Tutorial-php.cn

1. Mathematical function

ABS(x) returns the absolute value of x
BIN(x) returns the binary (OCT) of x Returns octal, HEX returns hexadecimal)
CEILING(x) Returns the smallest integer value greater than x
EXP(x) Returns Value e (the base of natural logarithms) raised to the power x
FLOOR(x) Returns the largest integer value less than x
##GREATEST( x1,x2,…,xn) Returns the largest value in the set
LEAST(x1,x2,…,xn) Returns the smallest value in the set
LN(x) Returns the natural logarithm of x LOG(x,y) Returns the base y logarithm of x
MOD(x,y) Returns x /Module of y (remainder) PI() returns the value of pi (pi)
RAND() returns a random value between 0 and 1, which can be used by providing a parameter (seed) RAND() random number generator generates a specified value.
ROUND(x,y) returns the rounded value of parameter x with y decimal places
SIGN(x) returns the representative number x The value of the sign
SQRT(x) Returns the square root of a number
TRUNCATE(x,y) Returns the number x truncated to y Result with decimal places

2. Aggregation function

AVG(col) returns the average value of the specified column
MIN(col) returns the minimum value of the specified column
MAX(col) returns the maximum value of the specified column
SUM( col) Returns the sum of all values in the specified column
GROUP_CONCAT(col) Returns the result of the concatenation of column values belonging to a group

3. String function

ASCII(char) returns the ASCII code value of the character BIT_LENGTH(str) returns the bit length of the string
CONCAT(s1,s2…,sn) concatenates s1,s2…,sn into a string
CONCAT_WS(sep,s1,s2…,sn) concatenates s1,s2…, sn is concatenated into a string, and separated by sep characters
INSERT(str,x,y,instr) Replace the string str with a substring that is y characters long starting from the x-th position For the string instr, return the result
FIND_IN_SET(str,list) analyzes the comma-separated list list. If str is found, return the position of str in the list
LCASE(str) or LOWER(str) returns the result of changing all characters in the string str to lowercase
LEFT(str,x) returns the string str The leftmost x characters in
LENGTH(s) returns the number of characters in string str
LTRIM(str) from string Cut off the leading spaces in str
POSITION(substr,str) Returns the position where the substring substr first appears in the string str
QUOTE(str) Use backslash to escape single quotes in str
REPEAT(str,srchstr,rplcstr) returns the result of string str repeated x times
REVERSE(str) Returns the result of reversing the string str
RIGHT(str,x) Returns the rightmost x characters in the string str
RTRIM(str) returns the space at the end of the string str
STRCMP(s1,s2) compares the strings s1 and s2
TRIM(str) removes all spaces at the beginning and end of the string
UCASE(str) or UPPER(str) returns all characters in the string str The result after capitalization

4, date and time function

##MONTHNAME(CURRENT_DATE);
##NOW() returns the current date and time
QUARTER(date) Returns the quarter (1~4) of date in the year, such as SELECT QUARTER(CURRENT_DATE);
WEEK(date) Returns the date date is the week of the year (0~53)
YEAR(date) Returns the year of date (1000~9999) Some examples: Get the current system time:

SELECT FROM_UNIXTIME(UNIX_TIMESTAMP());
SELEC TEXTRACT(YEAR_MONTH FROM CURRENT_DATE);
SELECT EXTRACT(DAY_SECOND FROM CURRENT_DATE);
SELECT EXTRACT(HOUR_MINUTE FROM CURRENT_DATE);
Returns the difference (number of months) between two date values:
SELECT PERIOD_DIFF(200302,199802)

Calculate age in Mysql:

SELECT DATE_FORMAT(FROM_DAYS(TO_DAYS(NOW())-TO_DAYS(birthday)),'%Y')+0 AS age FROM employee;
In this way, if Brithday is the year, month and day in the future, the calculation result is 0.

#The following SQL statement calculates the absolute age of an employee, that is, when Birthday is a date in the future, a negative value will be obtained.
SELECT DATE_FORMAT(NOW(), '%Y') - DATE_FORMAT(birthday, '%Y') -(DATE_FORMAT(NOW(), '00-%m-%d ')

5. Encryption function

AES_ENCRYPT(str,key): Returns the key key to the string str using the Advanced Encryption Standard The result of algorithm encryption, the result of calling AES_ENCRYPT is a binary string, stored in BLOB type
AES_DECRYPT(str,key) returns the key key to use advanced encryption on the string str The result after standard algorithm decryption
DECODE(str,key): Use key as the key to decrypt the encrypted string str
ENCRYPT(str , salt): Use the UNIXcrypt() function to encrypt the string str
ENCODE(str,key) with the keyword salt (a string that can uniquely determine the password, just like a key) ): Use key as the key to encrypt the string str. The result of calling ENCODE() is a binary string, which is stored in the BLOB type
MD5() Calculate the MD5 of the string str Checksum
##PASSWORD(str) Returns the encrypted version of the string str. This encryption process is irreversible and uses a different algorithm from the UNIX password encryption process.
SHA() Calculates the Secure Hash Algorithm (SHA) checksum of the string str
SELECT ENCRYPT('root',' salt');
SELECT ENCODE('xufeng','key');
SELECT DECODE(ENCODE('xufeng','key'),'key');
#Encryption and decryption together
SELECT AES_ENCRYPT('root','key');
SELECT AES_DECRYPT(AES_ENCRYPT('root','key'),'key');
SELECT MD5('123456');
SELECT SHA('123456');

MySQL has 4 functions used to perform conditional operations. These functions can implement SQL Conditional logic allows developers to convert some application business logic to the database backend.

If testN is If true, return resultN, otherwise return default
##NULLIF(arg1,arg2) If arg1=arg2, return NULL; otherwise return arg1
The first of these functions is IFNULL(), which has two parameters and evaluates the first parameter. If the first parameter is not NULL, the function will return the first parameter to the caller; if it is NULL, the second parameter will be returned.
For example: SELECT IFNULL(1,2), IFNULL(NULL,10),IFNULL(4*NULL,'false'); The NULLIF() function will check the two provided Whether the parameters are equal. If they are equal, NULL is returned. If they are not equal, the first parameter is returned.
For example: SELECT NULLIF(1,1),NULLIF('A','B'),NULLIF(2+3,4+1);
Like the IF() function provided by many scripting languages, MySQL's IF() function can also create a simple conditional test. This function has three parameters. The first is the expression to be judged. If the expression is true, IF() will return the second parameter, if it is false, IF() will return the third parameter.
For example: SELECTIF(1<10,2,3),IF(56>100,'true','false');
IF() function is suitable to be used when there are only two possible results. However, in the real world, we may find that multiple branches are needed in a conditional test. In this case, MySQL provides the CASE function, which is the same as the switch-case conditional routine in PHP and Perl languages.
The format of the CASE function is somewhat complicated, usually as follows: CASE [expression to be evaluated] WHEN [val 1] THEN [result 1] WHEN [val 2] THEN [result 2] WHEN [ val 3] THEN [result 3] …… WHEN [val n] THEN [result n] ELSE [default result] END
Here, the first parameter is the value to be judged or expression, followed by a series of WHEN-THEN blocks, the first parameter of each block specifies the value to be compared, and if true, the result is returned. All WHEN-THEN blocks will end with an ELSE block. When END ends all outer CASE blocks, the default result specified by the ELSE block will be returned if each of the preceding blocks does not match. If no ELSE block is specified and all WHEN-THEN comparisons are false, MySQL will return NULL.
The CASE function has another syntax, which is sometimes very convenient to use, as follows: CASE WHEN [conditional test 1] THEN [result 1] WHEN [conditional test 2] THEN [result 2] ELSE [default result] END Under this condition, the result returned depends on whether the corresponding condition test is true.
Example:

mysql>SELECT CASE 'green' WHEN 'red' THEN 'stop' WHEN 'green ' THEN 'go' END;
SELECT CASE 9 WHEN 1 THEN 'a' WHEN 2 THEN 'b' ELSE 'N/A' END; SELECT CASE WHEN (2+2) =4 THEN 'OK' WHEN(2+2)<>4 THEN 'not OK' END ASSTATUS;
##SELECT Name,IF((IsActive = 1),'has Activated','Inactivated') AS RESULT FROMUserLoginInfo; SELECT fname,lname,(math+sci+lit) AS total, CASE WHEN (math+sci+lit) < 50 THEN 'D' WHEN (math+sci+lit ) BETWEEN 50 AND 150 THEN 'C' WHEN (math+sci+lit) BETWEEN 151 AND 250 THEN 'B' ELSE 'A' END AS grade FROM marks; SELECT IF(ENCRYPT('sue','ts')=upass ,'allow','deny') AS LoginResultFROM users WHERE uname = 'sue';#A login verification

7. Formatting function

DATE_FORMAT(date,fmt) Format the date value according to the string fmt
FORMAT(x,y) Format x into a comma-separated sequence of numbers, y is The number of decimal places in the result
INET_ATON(ip) Returns the numerical representation of the IP address
INET_NTOA(num) Returns the IP address represented by the number
TIME_FORMAT(time,fmt) Format the time value according to the string fmt
The simplest one is the FORMAT() function, which can format large values into A comma-separated human-readable sequence.
Example:

SELECT FORMAT(34234.34323432,3);
SELECT DATE_FORMAT(NOW(),'%W,%D %M %Y %r');
##SELECT DATE_FORMAT(NOW (),'%h:%i %p');
SELECT INET_ATON('10.122.89.47');
SELECT INET_NTOA (175790383);
8. Type conversion function

In order to convert data types, MySQL provides the CAST() function, which can convert Converts a value to the specified data type.

Types are: BINARY, CHAR, DATE, TIME, DATETIME, SIGNED, UNSIGNED

## Example:

SELECT CAST(NOW() AS SIGNED INTEGER),CURDATE()+0; 
SELECT ‘f’=BINARY ‘F’,’f’=CAST(‘F’ AS BINARY);

Copy after login

9. System information function

##DATABASE() returns the current database name

SELECT DATABASE(),VERSION(),USER();
SELECT BENCHMARK(9999999,LOG(RAND()*PI()));
#The In the example, MySQL calculates the LOG(RAND()*PI()) expression 9999999 times.
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