刚才SQL那道题的解决方法。。。

琴瑟琵琶

妈的，原来学校用的是oracle，操

DATE FormatWhen a DATE value is displayed, Oracle must first convert thatvalue from the special internal format to a printable string. The conversionis done by a function TO_CHAR, according to a DATE format.Oracle's default format for DATE is "DD-MON-YY". Therefore,when you issue the queryselect b from x;you will see something like:B
---------
01-APR-98Whenever a DATE value is displayed, Oracle will call TO_CHARautomatically with the default DATE format. However, you may overridethe default behavior by calling TO_CHAR explicitly with your ownDATE format. For example,SELECT TO_CHAR(b, 'YYYY/MM/DD') AS b
FROM x;returns the result:B
---------------------------------------------------------------------------
1998/04/01The general usage of TO_CHAR is:TO_CHAR(<date>, '<format>')where the <format> string can be formed from over 40 options.Some of the more popular ones include:
, for example.

MM	Numeric month (e.g., 07)
MON	Abbreviated month name (e.g., JUL)
MONTH	Full month name (e.g., JULY)
DD	Day of month (e.g., 24)
DY	Abbreviated name of day (e.g., FRI)
YYYY	4-digit year (e.g., 1998)
YY	Last 2 digits of the year (e.g., 98)
RR	Like YY, but the two digits are ``rounded'' to a year inthe range 1950 to 2049.Thus, 06 is considered 2006 insteadof 1906
AM (or PM)	Meridian indicator
HH	Hour of day (1-12)
HH24	Hour of day (0-23)
MI	Minute (0-59)
SS	Second (0-59)

You have just learned how to output a DATE value using TO_CHAR.Now what about inputting a DATE value? This is done through afunction called TO_DATE, which converts a string to a DATEvalue, again according to the DATE format. Normally, you do nothave to call TO_DATE explicitly: Whenever Oracle expects a DATEvalue, it will automatically convert your input string using TO_DATEaccording to the default DATE format "DD-MON-YY". Forexample, to insert a tuple with a DATE attribute, you can simplytype:
insert into x values(99, '31-may-98');Alternatively, you may use TO_DATE explicitly:insert into x
values(99, to_date('1998/05/31:12:00:00AM', 'yyyy/mm/dd:hh:mi:ssam'));The general usage of TO_DATE is:TO_DATE(<string>, '<format>')where the <format> string has the same options as in TO_CHAR.Finally, you can change the default DATE format of Oracle from"DD-MON-YY" to something you like by issuing the following commandin sqlplus:
alter session set NLS_DATE_FORMAT='<my_format>';The change is only valid for the current sqlplus session.The Current TimeThe built-in function SYSDATE returns a DATE value containingthe current date and time on your system. For example,select to_char(sysdate, 'Dy DD-Mon-YYYY HH24:MI:SS') as "Current Time"
from dual;returnsCurrent Time
---------------------------------------------------------------------------
Tue 21-Apr-1998 21:18:27which is the time when I was preparing this document :-) Two interestingthings to note here:

• You can use double quotes to make names case sensitive (by default, SQLis case insensitive), or to force spaces into names. Oracle will treateverything inside the double quotes literally as a single name. In thisexample, if "Current Time" is not quoted, it would have been interpretedas two case insensitive names CURRENT and TIME,which would actually cause a syntax error.
• DUAL is built-in relation in Oracle which serves as a dummy relationto put in the FROM clause when nothing else is appropriate. Forexample, try "select 1+2 from dual;".

Another name for the built-in function SYSDATE is CURRENT_DATE.Be aware of these special names to avoid name conflicts.

zamble

????

国妓米兰

这边好像学校都是用的Oracle，很少用sql

姐夫戏小姨

我们也是用的Oracle

OruA

？？？？

琴瑟琵琶

O老师懂SQL吗？有时间找你赐教啊