Mysql commonly used date comparison and computing functions, mysql computing functions

Mysql commonly used date comparison and computing functions, mysql computing functions

Implementation of time comparison in MySql

Unix_timestamp ()

The unix_timestamp function accepts or does not use a parameter.

The return value is an unsigned integer. If the parameter is not used, it returns the number of seconds that have elapsed since 00:00:00, January 1, January 1, 1970,

If you use a parameter, the type of the parameter is time or time string, it is the number of seconds from 00:00:00 to the specified time.

With this function, you can naturally convert the time comparison into a comparison of unsigned integers.

For example, to determine whether a time is within a range

unix_timestamp( time ) between unix_timestamp( 'start ') and unix_timestamp( 'end' ) 

Here is an example of using the date function.

The following query Selects all records. The value of date_col is within the last 30 days:

mysql> SELECT something FROM table WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;

DAYOFWEEK (date)

Returns the index of the week of the date (1 = Sunday, 2 = Monday ,...... 7 = Saturday ). These index values correspond to the ODBC standard.

mysql> select DAYOFWEEK('1998-02-03');-> 3

WEEKDAY (date)

Returns the week index of date (0 = Monday, 1 = Tuesday ,...... 6 = Sunday ).

mysql> select WEEKDAY('1997-10-04 22:23:00');-> 5mysql> select WEEKDAY('1997-11-05');-> 2 

DAYOFMONTH (date)

Returns the date of a month in the range of 1 to 31.

mysql> select DAYOFMONTH('1998-02-03');-> 3

DAYOFYEAR (date)

Returns the number of days in a year from 1 to 366.

mysql> select DAYOFYEAR('1998-02-03');-> 34 

MONTH (date)

Returns the month of date, ranging from 1 to 12.

mysql> select MONTH('1998-02-03');-> 2

DAYNAME (date)

Returns the week name of date.

mysql> select DAYNAME("1998-02-05");-> 'Thursday'

MONTHNAME (date)

Returns the month name of date.

mysql> select MONTHNAME("1998-02-05");-> 'February'

QUARTER (date)

Returns the quarter of a year from date, ranging from 1 to 4.

mysql> select QUARTER('98-04-01');-> 2

WEEK (date)

WEEK (date, first)

If Sunday is the first day of a week, there is a single parameter that returns the number of weeks of the date, ranging from 0 to 52. Two Parameter formats: WEEK () allows you to specify whether the WEEK starts on Sunday or Monday. If the second parameter is 0, the week starts from Sunday, and if the second parameter is 1, it starts from Monday.

mysql> select WEEK('1998-02-20');-> 7mysql> select WEEK('1998-02-20',0);-> 7mysql> select WEEK('1998-02-20',1);-> 8

YEAR (date)

Returns the year of date, ranging from 1000 to 9999.

mysql> select YEAR('98-02-03');-> 1998

HOUR (time)

Returns the hour of time, ranging from 0 to 23.

mysql> select HOUR('10:05:03');-> 10

MINUTE (time)

Returns the minute of time, ranging from 0 to 59.

mysql> select MINUTE('98-02-03 10:05:03');-> 5 

SECOND (time)

The number of seconds for the return time, ranging from 0 to 59.

mysql> select SECOND('10:05:03');-> 3

PERIOD_ADD (P, N)

Add N months to phase P (in the format of YYMM or YYYYMM ). Return Value in the format of YYYYMM. Note that the phase parameter P is not a date value.

mysql> select PERIOD_ADD(9801,2);-> 199803

PERIOD_DIFF (P1, P2)

Returns the number of months between period P1 and P2. P1 and P2 should be in the format of YYMM or YYYYMM. Note that the period parameters P1 and P2 are not date values.

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)

These functions perform date operations. For MySQL 3.22, they are new. ADDDATE () and SUBDATE () are synonyms of DATE_ADD () and DATE_SUB.

In MySQL 3.23, you can use + and-instead of DATE_ADD () and DATE_SUB (). (See the example) date is a DATETIME or DATE value that specifies the start date. expr is an expression that specifies the interval value added to the start DATE or subtracted from the start date. expr is a string; it can start with a "-" to indicate the negative interval. Type is a keyword that specifies how the expression should be interpreted. The EXTRACT (type FROM date) function returns the "type" interval FROM the date. The following table shows how the type and expr parameters are associated: The type value indicates the expected expr format.

SECOND SECONDS
MINUTE MINUTES
HOUR time HOURS
DAY DAYS
MONTH-MONTH MONTHS
YEAR YEARS
MINUTE_SECOND MINUTES and SECONDS "MINUTES: SECONDS"
HOUR_MINUTE hour and minute "HOURS: MINUTES"
DAY_HOUR and hour "days hours"
YEAR_MONTH and month "YEARS-MONTHS"
HOUR_SECOND hour, minute, "HOURS: MINUTES: SECONDS"
DAY_MINUTE day, hour, minute "days hours: MINUTES"
DAY_SECOND day, hour, minute, second "days hours: MINUTES: SECONDS"

MySQL allows any punctuation Separator in the expr format. It indicates that the recommended Delimiter is displayed. If the date parameter is a DATE value and your calculation only contains the YEAR, MONTH, and DAY sections (that is, there is no time section), the result is a DATE value. Otherwise, the result is a DATETIME value.

mysql> SELECT "1997-12-31 23:59:59" + INTERVAL 1 SECOND;-> 1998-01-01 00:00:00mysql> SELECT INTERVAL 1 DAY + "1997-12-31";-> 1998-01-01mysql> SELECT "1998-01-01" - INTERVAL 1 SECOND;-> 1997-12-31 23:59:59mysql> SELECT DATE_ADD("1997-12-31 23:59:59",INTERVAL 1 SECOND);-> 1998-01-01 00:00:00mysql> SELECT DATE_ADD("1997-12-31 23:59:59",INTERVAL 1 DAY);-> 1998-01-01 23:59:59mysql> SELECT DATE_ADD("1997-12-31 23:59:59",INTERVAL "1:1" MINUTE_SECOND);-> 1998-01-01 00:01:00mysql> SELECT DATE_SUB("1998-01-01 00:00:00",INTERVAL "1 1:1:1" DAY_SECOND);-> 1997-12-30 22:58:59mysql> SELECT DATE_ADD("1998-01-01 00:00:00",INTERVAL "-1 10" DAY_HOUR);-> 1997-12-30 14:00:00mysql> SELECT DATE_SUB("1998-01-02", INTERVAL 31 DAY);-> 1997-12-02mysql> SELECT EXTRACT(YEAR FROM "1999-07-02");-> 1999mysql> SELECT EXTRACT(YEAR_MONTH FROM "1999-07-02 01:02:03");-> 199907mysql> SELECT EXTRACT(DAY_MINUTE FROM "1999-07-02 01:02:03");-> 20102

If you specify an interval value that is too short (excluding the expected interval of the type keyword), MySQL assumes that you have saved the leftmost portion of the interval value. For example,

If you specify a type of DAY_SECOND, the value of expr is expected to be one day, hour, minute, and second. If you specify a value like,

MySQL assumes that the days and hours are lost and the values represent minutes and seconds. In other words, "" DAY_SECOND is equivalent"

The MINUTE_SECOND method is used to explain the TIME value of MySQL, which indicates the elapsed TIME instead of the one-day TIME. If you use an incorrect date,

The result is NULL. If you increase MONTH, YEAR_MONTH, or YEAR and the result date is greater than the maximum number of days of the new MONTH, the day is adjusted by the maximum number of days of the new moon.

mysql> select DATE_ADD('1998-01-30', Interval 1 month);-> 1998-02-28

Note: In the previous example, the INTERVAL and type keywords are not case sensitive.

TO_DAYS (date)

Returns the number of days (from 0 years ).

mysql> select TO_DAYS(950501);-> 728779mysql> select TO_DAYS('1997-10-07');-> 729669

FROM_DAYS (N)

Returns a DATE value for the number of days N.

mysql> select FROM_DAYS(729669);-> '1997-10-07'

DATE_FORMAT (date, format)

Format the date value based on the format string. The following modifier can be used in the format string: % M month name (January ...... December)

% W name of the Week (Sunday ...... Saturday)
% D Date of the month with an 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 (00 ...... 31)
% E number of days in the month (0 ...... 31)
% M month, number (01 ...... 12)
% C month, number (1 ...... 12)
% B abbreviated month name (Jan ...... Dec)
% J days in a year (001 ...... 366)
% H hour (00 ...... 23)
% K hour (0 ...... 23)
% H hour (01 ...... 12)
% I hour (01 ...... 12)
% L hour (1 ...... 12)
% I minute, number (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 days in a week (0 = Sunday ...... 6 = Saturday)
% U Week (0 ...... 52). Sunday is the first day of the week.
% U Week (0 ...... 52) Monday is the first day of the week.
% A text "%"

All other characters are not interpreted and copied to the result.

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'

In MySQL3.23, % is required before the format modifier. In earlier MySQL versions, % is optional.

TIME_FORMAT (time, format)

This is used like the preceding DATE_FORMAT () function, but the format string can only contain format modifiers for processing hours, minutes, and seconds. Other modifiers generate a NULL value or 0.

CURDATE ()

CURRENT_DATE returns today's date value in 'yyyy-MM-DD 'or YYYYMMDD format, depending on whether the function is used in a string or numeric context.

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, depending on whether the function is used in a string or in the context of a number.

mysql> select CURTIME();-> '23:50:26'mysql> select CURTIME() + 0;-> 235026

NOW ()

SYSDATE ()

CURRENT_TIMESTAMP returns the current date and time in 'yyyy-MM-DD HH: MM: ss' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or in the context of a number.

mysql> select NOW();-> '1997-12-15 23:50:26'mysql> select NOW() + 0;-> 19971215235026

UNIX_TIMESTAMP ()
UNIX_TIMESTAMP (date)
If no parameter is called, a Unix timestamp (in seconds starting from '2017-01-01 00:00:00 'GMT) is returned ). If UNIX_TIMESTAMP () is called with a date parameter, it returns the second value starting from '2017-01-01 00:00:00 'GMT. Date can be a number of a DATE string, a datetime string, a TIMESTAMP, or a local time in YYMMDD or YYYYMMDD format.

mysql> select UNIX_TIMESTAMP();-> 882226357mysql> select UNIX_TIMESTAMP('1997-10-04 22:23:00');-> 875996580

When UNIX_TIMESTAMP is used in a TIMESTAMP column, the function accepts the value directly without the implicit "string-to-unix-timestamp" transformation.

FROM_UNIXTIME (unix_timestamp)

Returns the value represented by the unix_timestamp parameter in 'yyyy-MM-DD HH: MM: ss' or YYYYMMDDHHMMSS format, depending on the function being in a string
Or a digital context.

mysql> select FROM_UNIXTIME(875996580);-> '1997-10-04 22:23:00'mysql> select FROM_UNIXTIME(875996580) + 0;-> 19971004222300

FROM_UNIXTIME (unix_timestamp, format)

Returns a string representing the Unix time mark, formatted according to the format string. Format can contain the same modifier as the entries listed by the DATE_FORMAT () function.

mysql> select FROM_UNIXTIME(UNIX_TIMESTAMP(),'%Y %D %M %h:%i:%s %x');-> '1997 23rd December 03:43:30 x'

SEC_TO_TIME (seconds)

Returns the seconds parameter, which is converted to hour, minute, and second. The value is formatted in 'hh: MM: ss' or HHMMSS, depending on whether the function is used in a string or a number context.

mysql> select SEC_TO_TIME(2378);-> '00:39:38'mysql> select SEC_TO_TIME(2378) + 0;-> 3938

TIME_TO_SEC (time)

Returns the time parameter, which is converted to seconds.

mysql> select TIME_TO_SEC('22:23:00');-> 80580mysql> select TIME_TO_SEC('00:39:38');-> 2378

Mysql has many date functions. functions used for date comparison are sometimes not necessarily a function that may be used together by multiple functions. Therefore, you must use your imagination.