1. The string function
ascii (str)
returns the ascii value of the first character of the string str (returns 0 when str is an empty string)
mysql> select ascii('2');
-> 50
mysql> select ascii(2) ;
-> 50
mysql> select ascii('dete');
-> 100
ord(str)
returns the same value as the ascii() function returns if the beginning of the string str is a single byte.
If it is a multi-byte character, return in the format ((first byte ascii code)*256+(second byte ascii code))[*256+third byte asciicode...] mysql> select ord('2')
;
- > 50
conv(n,from_base,to_base)
converts the number n base and returns it as a string (null is returned when any parameter is null, the base range is 2-36 base, when to_base is a negative number, n is used as a valid number) Signed number otherwise unsigned number, conv works with 64-bit precision)
mysql> select conv("a",16,2);
-> '1010'
mysql> select conv("6e",18,8);
- > '172'
mysql> select conv(-17,10,-18);
-> '-h'
mysql> select conv(10+"10"+'10'+0xa,10,10);
-> '40 '
bin(n)
converts n into a binary value and returns it as a string (n is a bigint number, equivalent to conv(n,10,
Convert n to octal value and return it as a string (n is a bigint number, equivalent to conv(n,10,8))
mysql> select oct(12);
-> '14'
hex(n)
convert n to Hexadecimal and returned as a string (n is a bigint number, equivalent to conv(n,10,16))
mysql> select hex(255);
-> 'ff'
char(n,...)
returned by A string composed of ASCII code characters corresponding to parameters n,... (parameters are n,... are numeric sequences, and null values are skipped)
mysql> select char(77,121,83,81,'76');
-> 'mysql'
mysql> select char(77,77.3,'77.3');
-> 'mmm'
concat(str1, str2,...)
concatenates the parameters into a long string and returns it (when any parameter is null Return null)
mysql> select concat('my', 's', 'ql');
-> 'mysql'
mysql> select concat('my', null, 'ql');
-> null
mysql> select concat(14.3);
-> '14.3'
length(str)
octet_length(str)
char_length(str)
character_length(str)
returns the length of the string str (for multi-byte characters char_length is only calculated once)
mysql> select length('text');
-> 4
mysql> select octet_length('text' );
-> 4
locate(substr,str)
position(substr in str)
returns the position where the string substr appears for the first time in the string str (returns 0 when str does not contain substr)
mysql> select locate('bar', ' foobarbar');
-> 4
mysql> select locate('xbar', 'foobar');
-> 0
locate(substr, str, pos)
returns the first occurrence of the string substr starting from the pos position of the string str position (returns 0 when str does not contain substr)
mysql> select locate('bar', 'foobarbar',5);
-> 7
instr(str,
substr) returns the position of the first occurrence of string substr in string str (returns 0 when str does not contain substr)
mysql> select instr('foobarbar', 'bar');
-> 4
mysql> select instr('xbar', 'foobar');
-> 0
lpad(str,len,padstr)
fills the left end of str with the string padstr until The length of the string is len and returns
mysql> select lpad('hi',4,'??');
-> '??hi'
rpad(str,len,padstr)
fills the right end of str with the string padstr until the length of the string is len and returns
mysql> select rpad('hi',5,'?');
-> 'hi???'
left(str,len)
returns the left end of the string str len characters
mysql> select left('foobarbar ', 5);
-> 'fooba'
right(str,len)
returns len characters from the right end of the string str
mysql> select right('foobarbar', 4);
-> 'rbar'
substring(str,pos,len)
substring(str from pos for len)
mid(str,pos,len)
Returns the position of string str starting from pos len characters mysql> select substring('quadratically',5,6); ->
'ratica'
substring(str,pos)
substring(str from pos)
returns the position of string str starting from pos A substring of
mysql> select substring('quadratically',5);
-> 'ratically'
mysql> select substring('foobarbar' from 4);
-> 'barbar'
substring_index(str,delim,count)
returns the string from The substring after the delimiter delim that appears in the countth occurrence of str
(the left end is returned when count is a positive number, otherwise the right end substring is returned)
mysql> select substring_index('www.mysql.com', '.', 2);
- > 'www.mysql'
mysql> select substring_index('www.mysql.com', '.', -2);
-> 'mysql. com'
ltrim(str)
returns the string str with the left space removed
mysql> select ltrim(' barbar');
-> 'barbar'
rtrim(str)
returns the string str with the right space removed
mysql> select rtrim('barbar ');
-> 'barbar'
trim([[both | leading | trailing] [remstr] from] str)
returns prefix or suffix remstr The deleted string str (positional parameters default to both, remstr default value is space)
mysql> select trim(' bar ');
-> 'bar'
mysql> select trim (leading 'x' from 'xxxbarxxx');
- > 'barxxx'
mysql> select trim(both 'x' from 'xxxbarxxx');
-> 'bar'
mysql> select trim(trailing 'xyz' from 'barxxyz');
-> 'barx'
soundex(str)
returns str A homophone string ("roughly the same" sounding string has the same
homophone string, non-alphanumeric characters are ignored, Letters outside az are treated as vowels)
mysql> select soundex('hello');
-> 'h400'
mysql> select soundex('quadratically');
-> 'q36324'
space(n)
returns a string consisting of n space characters
mysql> select space(6);
-> ' '
replace(str, from_str, to_str)
uses the string to_str to replace the string str in substring from_str and return
mysql> select replace('www.mysql.com', 'w', 'ww'); -
> 'wwwwww.mysql.com'
repeat(str, count)
returns count strings str connected into a string (null
is returned when any parameter is null, and an empty string is returned when count<=0)
mysql> select repeat('mysql', 3);
-> 'mysqlmysqlmysql'
reverse(str)
reverses the string str character order and return
mysql> select reverse('abc');
-> 'cba'
insert(str,pos,len,
newstr) Replace the substring of string str that is len characters long starting from position pos with the string
newstr and return
mysql> select insert('quadratic', 3, 4, 'what');
-> 'quwhattic'
elt(n,str1,str2,str3,...)
returns the nth string (n is less than 1 or greater than the number of parameters, returns null)
mysql> select elt(1, 'ej', 'heja ', 'hej', 'foo');
-> 'ej'
mysql> select elt(4, 'ej', 'heja', 'hej', 'foo'); -
> 'foo'
field(str,str1 , str2, str3,...)
returns str equal to the serial number of the nth string following it (returns 0 if str is not found)
mysql> select field('ej', 'hej', 'ej', 'heja' , 'hej',
'foo');
-> 2
mysql> select field('fo', 'hej', 'ej', 'heja', 'hej', '
foo');
-> 0
find_in_set(str,
strlist) returns the serial number of str in the string set strlist (null is returned if any parameter is null
, 0 is returned if str is not found, and the operation is abnormal when parameter 1 contains ",")
mysql> select find_in_set('b','a, b,c,d');
-> 2
make_set(bits,str1,str2,...)
Convert the number of parameter 1 to binary. If the binary bit at a certain position is equal to 1, the
string at the corresponding position is selected into the string set and returned (the null string is not added to the result)
mysql> select make_set(1,'a' ,'b','c');
-> 'a'
mysql> select make_set(1 | 4,'hello','nice','world'); ->
'hello,world'
mysql> select make_set(0 ,'a','b','c');
-> ''
export_set(bits,on,off,[separator,[number_of_bits]])
arranges the string set by bits, and only inserts the string when the bit is equal to 1 on, otherwise insert
off (separator default value ",", when the number_of_bits parameter is used, the length is insufficient to fill in 0
and is truncated if it is too long)
mysql> select export_set(5,'y','n',',',4)
-> y ,n,y, n
lcase(str)
lower(str)
returns the lowercase string str
mysql> select lcase('quadratically');
-> 'quadratically'
ucase(str)
upper(str)
returns the uppercase string str
mysql> select ucase('quadratically');
-> 'quadratically'
load_file(file_name)
reads the file and returns the file content as a string (the file cannot be found, the path
is incomplete, there is no permission, and the length is greater than max_allowed_packet, null will be returned)
mysql > update table_name set blob_column=load_file
("/tmp/picture") where id=1;
2. The mathematical function
abs(n)
returns the absolute value of n
mysql> select abs(2);
-> 2
mysql> select abs(- 32);
-> 32
sign(n)
returns the sign of the parameter (is -1, 0 or 1)
mysql> select sign(-32);
-> -1
mysql> select sign(0);
-> 0
mysql> select sign(234);
-> 1
mod(n,m)
modulo operation, returns the remainder when n is divided by m (same as % operator)
mysql> select mod(234, 10);
-> 4
mysql> select 234 % 10;
-> 4
mysql> select mod(29,9);
-> 2
floor(n)
returns the largest integer value not greater than n
mysql> select floor(1.23);
-> 1
mysql> select floor(-1.23);
-> -2
ceiling(n)
returns the smallest integer value not less than n
mysql> select ceiling(1.23);
-> 2
mysql> select ceiling( -1.23);
-> -1
round(n,d)
returns the rounded value of n, retaining d decimal places (the default value of d is 0)
mysql> select round(-1.23);
-> -1
mysql> select round( -1.58);
-> -2
mysql> select round(1.58);
-> 2
mysql> select round(1.298, 1);
-> 1.3
mysql> select round(1.298, 0);
-> 1
exp(n)
returns the nth power of e (the base of natural logarithms)
mysql> select exp(2 );
-> 7.389056
mysql> select exp(-2);
-> 0.135335
log(n)
returns the natural logarithm of n
mysql> select log(2);
-> 0.693147
mysql> select log(-2);
-> null
log10(n)
returns the base 10 logarithm of n
mysql> select log10(2);
-> 0.301030
mysql> select log10(100);
-> 2.000000
mysql> select log10(-100);
-> null
pow(x ,y)
power(x,y)
returns the value x raised to the y power
mysql> select pow(2,2);
-> 4.000000
mysql> select pow(2,-2);
-> 0.250000 sqrt(n) returns the square root of a non-negative number n mysql> select sqrt(4); -> 2.000000 mysql> select sqrt(20); -> 4.472136 pi() returns pi mysql> select pi(); -> 3.141593 cos(n) returns the cosine value of n mysql> select cos(pi()); -> -1.000000 sin(n ) returns the sine value of n mysql> select sin(pi()); -> 0.000000 tan(n) returns the tangent value of n mysql> select tan(pi()+1); -> 1.557408 acos(n) returns the inverse of n Cosine (n is the cosine value, in the range of -1 to 1, otherwise null is returned)
mysql> select acos(1);
-> 0.000000
mysql> select acos(1.0001);
-> null
mysql> select acos(0);
-> 1.570796
asin(n)
returns n inverse sine value
mysql> select asin(0.2);
-> 0.201358
mysql> select asin('foo');
-> 0.000000
atan(n)
returns the arc tangent of n
mysql> select atan(2);
-> 1.107149
mysql> select atan(-2);
-> -1.107149
atan2(x,y)
returns the arctangent of two variables x and y (similar to the arctangent of y/x, the sign determines the quadrant)
mysql> select atan(-2,2);
-> -0.785398
mysql> select atan(pi (),0);
-> 1. 570796
cot(n)
returns the cotangent of x
mysql> select cot(12);
-> -1.57267341
mysql> select cot(0);
-> null
rand()
rand(n)
returns a random floating point value in the range 0 to 1.0 (you can use the number n as the initial value )
mysql> select rand();
-> 0.5925
mysql> select rand(20);
-> 0.1811
mysql> select rand(20);
-> 0.1811
mysql> select rand();
-> 0.2079
mysql> select rand();
-> 0.7888
degrees(n)
Convert n from radians to degrees and return
mysql> select degrees(pi());
-> 180.000000
radians(n)
Convert n from degrees to radians and return
mysql> select radians(90);
-> 1.570796 truncate(n, d)
Keep d decimal places of number n and return
mysql> select truncate(1.223,1);
-> 1.2
mysql> select truncate(1.999,1);
-> 1.9
mysql> select truncate(1.999,0);
-> 1
least( x,y,...)
returns the minimum value (if the return value is used in an integer (real or size-sensitive string) context or all arguments are integers (real or size-sensitive string) then they are treated as integers (real or size-sensitive string) Sensitive string) comparison, otherwise the case-insensitive string is compared)
mysql> select least(2,0);
-> 0
mysql> select least(34.0,3.0,5.0,767.0);
-> 3.0
mysql> select least("b","a","c");
-> "a"
greatest(x,y,...)
returns the maximum value (the rest are the same as least())
mysql> select greatest(2,0);
-> 2
mysql> select greatest(34.0,3.0,5.0,767. 0);
-> 767.0
mysql> select greatest("b","a","c");
-> "c" 3. The period time function dayofweek(date) returns the date date is the day of the week (1=Sunday, 2=Monday,... 7=Saturday, odbc standard) mysql> select dayofweek('1998-02-03'); -> 3 weekday(date) returns the day of the week date is (0=Monday, 1=Tuesday,...6=Sunday) . mysql> select weekday('1997-10-04 22:23:
Returns the month value in date
mysql> select month('1998-02-03');
-> 2
dayname(date)
returns the day of the week that date is (returned by English name)
mysql> select dayname("1998-02-05" );
-> 'thursday'
monthname(date)
returns the month of date (returned by English name)
mysql> select monthname("1998-02-05");
-> 'february'
quarter(date)
returns the year of date Which quarter
mysql> select quarter('98-04-01');
-> 2
week(date, first)
returns the date in which week of the year (first default value is 0, first value 1 means Monday is
The beginning of the week, 0 starts from Sunday)
mysql> select week('1998-02-20');
-> 7
mysql> select week('1998-02-20', 0);
-> 7
mysql> select week('1998-02-20',1);
-> 8
year(date)
returns the year of date (range is 1000 to 9999)
mysql> select year('98-02-03');
-> 1998
hour(time)
returns the hour of time (range is 0 to 23) )
mysql> select hour('10:05:03');
-> 10
minute(time)
returns the number of minutes of time (range is 0 to 59)
mysql> select minute('98-02-03 10:05:03 ');
-> 5
second(time)
returns the number of seconds of time (range is 0 to 59)
mysql> select second('10:05:03');
-> 3
period_add(p,n)
adds n months to Period p and returns (the format of p is yymm or yyyymm)
mysql> select period_add(9801,2);
-> 199803
period_diff(p1,p2)
returns the number of months between periods p1 and p2 (the format of p1 and p2 is yymm or yyyymm )
mysql> select period_diff(9802,199703);
-> 11
date_add(date,interval expr type)
date_sub(date,interval expr type)
adddate(date,interval expr type)
subdate(date,interval expr type)
add date and time Subtraction operations
(adddate() and subdate() are synonyms of date_add() and date_sub(). You
can also use operators + and - instead of functions.
date is a datetime or date value, and expr is a method for adding and subtracting dates. The expression
string type specifies how the expression expr should be interpreted
[type value meaning expected expr format]:
second seconds seconds
minute minutes minutes
hour time hours
day days days month months
months
year years years
minute_second minutes and seconds "minutes:seconds "
hour_minute hours and minutes "hours:minutes"
day_hour "days hours"
year_month "years-months"
hour_second "hours:minutes:seconds"
day_minute "days hours:minutes"
day_second day, hour, minute, second" days
hours:minutes:seconds"
expr allows any punctuation as a separator. If all are date values, the result is a
date value, otherwise the result is a datetime value.)
If the type keyword is incomplete, mysql takes the value from the right end, day_second Because
the hour and minute are missing, they are equal to minute_second)
If you add month, year_month or year, and the number of days is greater than the maximum number of days in the result month,
the maximum number of days is used)
mysql> select "1997-12-31 23:59:59" + interval 1 second;
- > 1998-01-01 00:00: 00
mysql> select interval 1 day + "1997-12-31";
-> 1998-01-01
mysql> select "1998-01-01" - interval 1 second;
-> 1997-12-31 23:59:59
mysql> select date_add("1997-12-31 23:59:59",interval 1
second);
-> 1998-01-01 00:00:00
mysql> select date_add("1997-12-31 23:59:59",interval 1
day);
-> 1998-01-01 23:59:59
mysql> select date_add("1997-12-31 23:59:59",interval
"1:1" minute_second);
-> 1998-01-01 00:01:00
mysql> select date_sub("1998-01-01 00:00:00",interval "1
1:1:1" day_second);
-> 1997-12-30 22:58:59
mysql> select date_add("1998-01-01 00:00:00", interval "-1
10" day_hour);
-> 1997-12-30 14:00:00
mysql> select date_sub("1998-01-02", interval 31 day);
-> 1997-12-02
mysql> select extract(year from "1999-07-02");
-> 1999
mysql> select extract(year_month from "1999-07-02
01:02:03");
-> 199907
mysql> select extract(day_minute from "1999-07-02
01:02:03");
-> 20102
to_days(date)
returns the number of days since AD 0 (not counting years before 1582)
mysql> select to_days(950501);
-> 728779
mysql > select to_days('1997-10-07');
-> 729669
from_days(n)
gives the number of days to return from year 0 to the present (not counting years before 1582)
mysql> select from_days(729669);
-> '1997 -10-07'
date_format(date,
format) Format the date value according to the format string
(available identifiers in the format string:
%m month name (january...december)
%w week name (sunday...saturday)
%d day of the month with English prefix (1st, 2nd, 3rd, etc.)
%y year, number, 4 digits
%y Year, number, 2 digits
%a abbreviated name of the week (sun...sat)
%d number of days in the month, number (00...31)
%e number of days in the month, number (0...31)
%m month, Number (01...12)
%c month, number (1...12)
%b abbreviated month name (jan...dec)
%j number of days in a year (001...366)
%h hour (00... 23)
%k hours (0...23)
%h hours (01...12)
%i hours (01...12)
%l hours (1...12)
%i minutes, numbers (00...59)
% r Time, 12 hours (hh:mm:ss [ap]m)
%t Time, 24 hours (hh:mm:ss)
%s seconds (00……59)
%s seconds (00……59)
%p am or pm
%w The number of days in a week (0=sunday...6=saturday)
%u The week (0...52), where Sunday is the first day of the week
%u The week (0...52), where Monday is the day of the week The first day
%% character %)
mysql> select date_format('1997-10-04 22:23:00','%w %m %
y');
-> 'saturday october 1997'
mysql> select date_format(' 1997-10-04 22:23:00','%h:%i:%
s');
-> '22:23:00'
mysql> select date_format('1997-10-04 22:23:00' ,'%d %y %a
%d %m %b %j');
-> '4th 97 sat 04 10 oct 277'
mysql> select date_format('1997-10-04 22:23:00','% h %k %i
%r %t %s %w');
-> '22 22 10 10:23:00 pm 22:23:00 00 6'
time_format(time,
format) is similar to date_format(), but time_format only handles hours, minutes, and seconds (other
symbols produce a null value or 0)
curdate()
current_date() returns the current date value in 'yyyy-mm-dd' or yyyymmdd format ( either a string or a number depending on the context
of the return value ) mysql> select curdate(); -> '1997-12-15' mysql> select curdate() + 0; -> 19971215 curtime() current_time() returns the current time value in 'hh:mm:ss' or hhmmss format (the return value is a string or a number depending on the context ) mysql> select curtime(); -> '23:50:26' mysql> select curtime() + 0; -> 235026 now() sysdate() current_timestamp() in 'yyyy-mm-dd hh:mm:ss' or yyyymmddhhmmss format Returns the current date and time (either a string or a number depending on the context of the return value) mysql> select now(); -> '1997-12-15 23:50: 26'
mysql> select now() + 0;
-> 19971215235026
unix_timestamp()
unix_timestamp(date)
returns a unix timestamp (the number of
seconds , the default value of date is the current time )
mysql> select unix_timestamp();
-> 882226357
mysql> select unix_timestamp('1997-10-04 22:23:00');
-> 875996580
from_unixtime(unix_timestamp)
with 'yyyy-mm-dd hh:mm:ss' Or return
the value of the timestamp in yyyymmddhhmmss format (it is a string or a number according to the context of the return value)
mysql> select from_unixtime(875996580);
-> '1997-10-04 22:23:00'
mysql> select from_unixtime(875996580) + 0;
-> 19971004222300
from_unixtime(unix_timestamp,
format) returns the value of the timestamp in format string format
mysql> select from_unixtime(unix_timestamp(),'%y %d %m %
h:%i:%s %x');
-> '1997 23rd December 03:43:30 x'
sec_to_time(seconds)
with 'hh: mm:ss' or hhmmss format returns the time value converted from seconds (the return value is a string or a number depending on the context)
mysql> select sec_to_time(2378);
-> '00:39:38'
mysql> select sec_to_time( 2378) + 0;
-> 3938
time_to_sec(time)
returns the number of seconds in the time value
mysql> select time_to_sec('22:23:00');
-> 80580
mysql> select time_to_sec('00:39: 38');
-> 2378
conversion function
cast
usage: cast (field as data type) [Of course, whether the conversion can be successful depends on the issues that need to be paid attention to when the data type is forced to be converted]
Example: select cast (a as unsigned) as b from cardserver where order by b desc;
convert：
Usage: convert (field, data type)
Example: select convert (a, unsigned) as b from carderver where order by b desc;
Source: https://blog.csdn.net/qq_42239765/article/details/83898664