Date and Time Functions

Introduction
These functions allow you to get the date and time from the server where your PHP scripts are running. You can use these functions to format the date and time in many different ways.
Note: Please keep in mind that these functions are dependent on the locale settings of your server. Make sure to take daylight saving time (use e.g. $date = strtotime('+7 days', $date) and not $date += 7*24*60*60) and leap years into consideration when working with these functions.
Requirements
No external libraries are needed to build this extension.

Predefined Constants
The following constants are defined since PHP 5.1.1 and they offer standard date representations, which can be used along with the date format functions (like date()).


DATE_ATOM (string)
Atom (example: 2005-08-15T15:52:01+00:00)

DATE_COOKIE (string)
HTTP Cookies (example: Monday, 15-Aug-05 15:52:01 UTC)

DATE_ISO8601 (string)
ISO-8601 (example: 2005-08-15T15:52:01+0000)

DATE_RFC822 (string)
RFC 822 (example: Mon, 15 Aug 05 15:52:01 +0000)

DATE_RFC850 (string)
RFC 850 (example: Monday, 15-Aug-05 15:52:01 UTC)

DATE_RFC1036 (string)
RFC 1036 (example: Mon, 15 Aug 05 15:52:01 +0000)

DATE_RFC1123 (string)
RFC 1123 (example: Mon, 15 Aug 2005 15:52:01 +0000)

DATE_RFC2822 (string)
RFC 2822 (Mon, 15 Aug 2005 15:52:01 +0000)

DATE_RFC3339 (string)
Same as DATE_ATOM (since PHP 5.1.3)

DATE_RSS (string)
RSS (Mon, 15 Aug 2005 15:52:01 +0000)

DATE_W3C (string)
World Wide Web Consortium (example: 2005-08-15T15:52:01+00:00)

Following constants exists since PHP 5.1.2 and specify a format returned by functions date_sunrise() and date_sunset().


SUNFUNCS_RET_TIMESTAMP (integer)
Timestamp

SUNFUNCS_RET_STRING (integer)
Hours:minutes (example: 08:02)

SUNFUNCS_RET_DOUBLE (integer)
Hours as floating point number (example 8.75)

checkdate -- Validate a Gregorian date
date_create -- Returns new DateTime object
date_date_set -- Sets the date
date_default_timezone_get -- Gets the default timezone used by all date/time functions in a script
date_default_timezone_set -- Sets the default timezone used by all date/time functions in a script
date_format -- Returns date formatted according to given format
date_isodate_set -- Sets the ISO date
date_modify -- Alters the timestamp
date_offset_get -- Returns the daylight saving time offset
date_parse -- Returns associative array with detailed info about given date
date_sun_info -- Returns an array with information about sunset/sunrise and twilight begin/end
date_sunrise -- Returns time of sunrise for a given day and location
date_sunset -- Returns time of sunset for a given day and location
date_time_set -- Sets the time
date_timezone_get -- Return time zone relative to given DateTime
date_timezone_set -- Sets the time zone for the DateTime object
date -- Format a local time/date
getdate -- Get date/time information
gettimeofday -- Get current time
gmdate -- Format a GMT/UTC date/time
gmmktime -- Get Unix timestamp for a GMT date
gmstrftime -- Format a GMT/UTC time/date according to locale settings
idate -- Format a local time/date as integer
localtime -- Get the local time
microtime -- Return current Unix timestamp with microseconds
mktime -- Get Unix timestamp for a date
strftime -- Format a local time/date according to locale settings
strptime -- Parse a time/date generated with strftime()
strtotime -- Parse about any English textual datetime description into a Unix timestamp
time -- Return current Unix timestamp
timezone_abbreviations_list -- Returns associative array containing dst, offset and the timezone name
timezone_identifiers_list -- Returns numerically index array with all timezone identifiers
timezone_name_from_abbr -- Returns the timezone name from abbrevation
timezone_name_get -- Returns the name of the timezone
timezone_offset_get -- Returns the timezone offset from GMT
timezone_open -- Returns new DateTimeZone object
timezone_transitions_get -- Returns all transitions for the timezone

What is the difference between CHAR and VARCHAR data types?

CHAR is a fixed length data type. CHAR(n) will take n characters of storage even if you enter less than n characters to that column. For example, "Hello!" will be stored as "Hello! " in CHAR(10) column.
VARCHAR is a variable length data type. VARCHAR(n) will take only the required storage for the actual number of characters entered to that column. For example, "Hello!" will be stored as "Hello!" in VARCHAR(10) column.

How can we encrypt and decrypt a data present in a mysql table using mysql?

AES_ENCRYPT() and AES_DECRYPT() .


Will comparison of string "10" and integer 11 work in PHP?

Yes, internally PHP will cast everything to the integer type, so numbers 10 and 11 will be compared.


What is the functionality of MD5 function in PHP?

string md5(string)
It calculates the MD5 hash of a string. The hash is a 32-character hexadecimal number.

How can I load data from a text file into a table?

The MySQL provides a LOAD DATA INFILE command. You can load data from a file. Great tool but you need to make sure that:a) Data must be delimited
b) Data fields must match table columns correctly
How can we know the number of days between two given dates using MySQL?

Use DATEDIFF()

SELECT DATEDIFF(NOW(),'2006-07-01');

How can we change the name of a column of a table?

This will change the name of column:
ALTER TABLE table_name CHANGE old_colm_name new_colm_name

How can we change the data type of a column of a table?

This will change the data type of a column:
ALTER TABLE table_name CHANGE colm_name same_colm_name [new data type]

What is the difference between GROUP BY and ORDER BY in SQL?

To sort a result, use an ORDER BY clause.
The most general way to satisfy a GROUP BY clause is to scan the whole table and create a new temporary table where all rows from each group are consecutive, and then use this temporary table to discover groups and apply aggregate functions (if any).
ORDER BY [col1],[col2],...[coln]; Tells DBMS according to what columns it should sort the result. If two rows will hawe the same value in col1 it will try to sort them according to col2 and so on.
GROUP BY [col1],[col2],...[coln]; Tells DBMS to group (aggregate) results with same value of column col1. You can use COUNT(col1), SUM(col1), AVG(col1) with it, if you want to count all items in group, sum all values or view average.