Hour 12, "Understanding Dates and Time"

Quiz Answers

1: From where is the system date and time normally derived?
A1: The system date is derived from the current date and time of the operating system on the host machine.
2: List the standard internal elements of a DATETIME value.
A2: YEAR, MONTH, DAY, HOUR, MINUTE, and SECOND.
3: What could be a major factor concerning the representation and comparison of date and time values if your company is an international organization?
A3: The awareness of time zones may be a concern.
4: Can a character string date value be compared to a date value defined as a valid DATETIME data type?
A4: A DATETIME data type cannot be accurately compared to a date value defined as a character string. The character string must first be converted to the DATETIME data type.

Exercise Answers

  1. Provide SQL code for the exercises given the following information:

    Use SYSDATE to represent the current date and time.

    Use the table called DATES.

    Use the TO_CHAR function to convert dates to character strings with the following syntax:

    TO_CHAR('EXPRESSION','DATE_PICTURE')

    Use the TO_DATE function to convert character strings to dates with the following syntax:

    TO_DATE('EXPRESSION','DATE_PICTURE')

Date picture information:

DATE PICTUREMEANING
MONTHMonth spelled out
DAYDay spelled out
DDDay of month, number
MMMonth of year, number
YYTwo-digit year
YYYYFour-digit year
MIMinutes of the hour
SSSeconds of the minute

1: Use Assuming today is 1999-12-31, convert the current date to the format December 31 1999.
A1: 
SELECT TO_CHAR(SYSDATE,'MONTH DD YYYY')
FROM DATES;

2: Use Convert the following string to DATE format:
'DECEMBER 31 1999'

A2: 
SELECT TO_DATE('DECEMBER 31 1999','MONTH DD YYYY')
FROM DATES;

3: Use Write the code to return the day of the week on which New Year's Eve of 1999 falls. Assume that the date is stored in the format 31-DEC-99, which is a valid DATETIME data type.
A3: 
SELECT TO_CHAR('31-DEC-99','DAY')
FROM DATES;

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