Ques 66. What Are Date and Time Functions in MySQL?
MySQL offers a number of functions for date and time values:
► ADDDATE(date, INTERVAL expr unit) - Adding days to a date. Same as DATE_ADD().
► ADDTIME(time1, time2) - Adding two time values together.
► CURDATE() - Returning the current date. Same as CURRENT_DATE().
► CURTIME() - Returning the current time. Same as CURRENT_TIME().
► DATE(expression) - Returning the date from the expression.
► DATEDIFF(date1, date2) - Returning dates difference in days.
► DATE_ADD(date, INTERVAL expr unit) - Adding days to a date.
► DATE_SUB(date, INTERVAL expr unit) - Subtracting days from a date.
► DATE_FORMAT(date, format) - Returning a character string representing a date.
► DAY(date) - Returning an integer representing the day of the month. Same as DAYOFMONTH()
► DAYNAME(date) - Returning the name of week day.
► DAYOFMONTH(date) - Returning an integer representing the day of the month.
► DAYOFWEEK(date) - Returning an integer representing the day of the week.
► DAYOFYEAR(date) - Returning an integer representing the day of the year.
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Ques 67. What Are the Differences between CHAR and VARCHAR?
CHAR and VARCHAR are both ASCII character data types by default. But they have the following major differences:
► CHAR stores values in fixed lengths. Values are padded with space characters to match the specified length.
► VARCHAR stores values in variable lengths. Values are not padded with any characters. But 1 or 2 extra bytes are added to store the length of the data.
The table below shows you a good comparison of CHAR and VARCHAR data types:
Value CHAR(4) Length
'' ' ' 4 bytes
'ab' 'ab ' 4 bytes
'abcd' 'abcd' 4 bytes
Value VARCHAR(4) Length
'' '' 1 byte
'ab' 'ab' 3 bytes
'abcd' 'abcd' 5 bytes
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Ques 68. What Is TIMESTAMP in MySQL?
A TIMESTAMP data type allows you to record a date and time like DATETIME data type. But it has some interesting features when used on a table column:
► The first TIMESTAMP column in a table will be assigned with the current date and time, if it is not listed in an INSERT statement.
► The first TIMESTAMP column in a table will be assigned with the current date and time, if it is not listed in an UPDATE statement.
► If a TIMESTAMP column is assigned with NULL, the current date and time will be persisted to this column.
► You can turn off the default current date and time on INSERT by defining the column with "DEFAULT 0".
► The tutorial exercise below provides you 2 equivalent ways to create a TIMESTAMP column:
CREATE TABLE links (lastDate TIMESTAMP);
CREATE TABLE links (lastDate TIMESTAMP
DEFAULT CURRENT_TIMESTAMP
ON UPDATE CURRENT_TIMESTAMP);
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Ques 69. What Are the Differences between BINARY and VARBINARY?
Both BINARY and VARBINARY are both binary byte data types. But they have the following major differences:
► BINARY stores values in fixed lengths. Values are padded with 0x00.
► VARBINARY stores values in variable lengths. Values are not padded with any bytes. But 1 or 2 extra bytes are added to store the length of the data.
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Ques 70. How Many Ways to Get the Current Time?
There are 8 ways to get the current time:
SELECT NOW() FROM DUAL;
2006-07-01 10:02:41
SELECT CURRENT_TIME() FROM DUAL;
10:02:58
SELECT SYSDATE() FROM DUAL;
2006-07-01 10:03:21
mysql> SELECT CURRENT_TIMESTAMP() FROM DUAL;
2006-07-01 10:04:03
SELECT LOCALTIME() FROM DUAL;
2006-07-01 10:07:37
mysql> SELECT LOCALTIMESTAMP() FROM DUAL;
2006-07-01 10:08:08
mysql> SELECT UTC_TIME() FROM DUAL;
14:09:22
mysql> SELECT UTC_TIMESTAMP() FROM DUAL;
2006-07-01 14:09:49