MySQL Questions et reponses d'entretien
Question 1. How To Enter Microseconds in SQL Statements?
If you want to enter microseconds in a SQL statements, you can enter them right after the time string as a 6-digit number delimited with '.'. '0' will be padded to right if not enough digits. Here are some good examples:
SELECT TIME('1997/01/31 09^26^50.123') FROM DUAL;
09:26:50.123000
SELECT TIME('1997/01/31 09^26^50.000123') FROM DUAL;
09:26:50.000123
Question 2. How To Convert Dates to Character Strings?
You can convert dates to character strings using the DATE_FORMAT(date, format) function. MySQL supports the following basic formatting codes:
► %a Abbreviated weekday name (Sun..Sat)
► %b Abbreviated month name (Jan..Dec)
► %c Month, numeric (0..12)
► %D Day of the month with English suffix (0th, 1st, 2nd, 3rd,...)
► %d Day of the month, numeric (00..31)
► %e Day of the month, numeric (0..31)
► %f Microseconds (000000..999999)
► %H Hour (00..23)
► %h Hour (01..12)
► %I Hour (01..12)
► %i Minutes, numeric (00..59)
► %j Day of year (001..366)
► %k Hour (0..23)
► %l Hour (1..12)
► %M Month name (January..December)
► %m Month, numeric (00..12)
► %p AM or PM
► %r Time, 12-hour (hh:mm:ss followed by AM or PM)
► %S Seconds (00..59)
► %s Seconds (00..59)
► %T Time, 24-hour (hh:mm:ss)
► %W Weekday name (Sunday..Saturday)
► %w Day of the week (0=Sunday..6=Saturday)
► %Y Year, numeric, four digits
► %y Year, numeric (two digits)
Question 3. How To Convert Character Strings to Dates?
If you have a character string that represents a date, and you want to convert it into a date value, you can use the STR_TO_DATE(string, format) function. STR_TO_DATE() shares the same formatting codes with DATE_FORMAT() function. The tutorial exercise below shows you some good examples:
SELECT STR_TO_DATE('Friday, January 31, 1997',
'%W, %M %e, %Y') FROM DUAL;
1997-01-31
SELECT STR_TO_DATE('Friday, January 31, 1997, 09:26:50 AM',
'%W, %M %e, %Y, %h:%i:%s %p') FROM DUAL;
1997-01-31 09:26:50
SELECT STR_TO_DATE('31-Jan-1997 09:26:50.000123',
'%d-%b-%Y %H:%i:%s.%f') FROM DUAL;
1997-01-31 09:26:50.000123
Question 4. What Are Date and Time Intervals?
A date and time interval is special value to be used to increment or decrement a date or a time at a given date or time unit. A data and time interval should be expression in the format of "INTERVAL expression unit", where "unit" and "expression" should follow these rules:
unit - expression value format
MICROSECOND - MICROSECONDS
SECOND - SECONDS
MINUTE - MINUTES
HOUR - HOURS
DAY - DAYS
WEEK - WEEKS
MONTH - MONTHS
QUARTER - QUARTERS
YEAR -YEARS
SECOND_MICROSECOND - 'SECONDS.MICROSECONDS'
MINUTE_MICROSECOND - 'MINUTES.MICROSECONDS'
MINUTE_SECOND - 'MINUTES:SECONDS'
HOUR_MICROSECOND - 'HOURS.MICROSECONDS'
HOUR_SECOND - 'HOURS:MINUTES:SECONDS'
HOUR_MINUTE - 'HOURS:MINUTES'
DAY_MICROSECOND - 'DAYS.MICROSECONDS'
DAY_SECOND - 'DAYS HOURS:MINUTES:SECONDS'
DAY_MINUTE - 'DAYS HOURS:MINUTES'
DAY_HOUR - 'DAYS HOURS'
YEAR_MONTH - 'YEARS-MONTHS'
Question 5. How To Increment Dates by 1 in MySQL?
If you have a date, and you want to increment it by 1 day, you can use the DATE_ADD(date, INTERVAL 1 DAY) function. You can also use the date interval add operation as "date + INTERVAL 1 DAY". The tutorial exercise below gives you some good examples:
SELECT DATE_ADD(DATE('1997-01-31'), INTERVAL 1 DAY)
FROM DUAL;
1997-02-01
SELECT DATE('1997-01-31') + INTERVAL 1 DAY FROM DUAL;
1997-02-01
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