Just a quicky on dates

Question

CREATE TABLE slaughter(
     Slaughter_No               Number(12)PRIMARY KEY,     
     Slaughter_Set               Varchar2(10)NOT NULL,
     Slaughter_Date               DATE,
     Disposal_Slaughterhouse_Code     Varchar2(15)NOT NULL,
     Diagnosis_Confirmation_No      Number(12)NOT NULL,
CONSTRAINT fk_sl_dc FOREIGN KEY (Diagnosis_Confirmation_No)
          references diagnosis(Diagnosis_Confirmation_No),
CONSTRAINT fk_sl_ds FOREIGN KEY (Disposal_Slaughterhouse_Code)
          references disposal_slaughterhouse(Disposal_Slaughterhouse_Code));
All I need to do is to create a query that will show me the Slaughter_No and the date of that particular slaughter, for the all the slaughters that have taken place in for example the last six months
If SQL was made for a simpleton like me I could do this:-
Select slaughter_no, Slaughter_Date
FROM slaughter
WHERE slaughter_date between 28-Feb-01 and 28-Mar-01
(n how I do i get round the fact that the stystem thinks
28-Feb-98 is greater than 28-Feb-01)

Answer 1

SQL> -- If your nls_date_format is set like this:
SQL> ALTER SESSION SET NLS_DATE_FORMAT = 'dd-Mon-yy'
  2  /
Session altered.
SQL> -- Your system will display the date like this:
SQL> SELECT SYSDATE
  2  FROM   DUAL
  3  /
SYSDATE                                
16-Jan-02                              
SQL> -- To see all four year digits:
SQL> SELECT TO_CHAR (SYSDATE, 'dd-Mon-yyyy')
  2  FROM   DUAL
  3  /
TO_CHAR(SYS                            
16-Jan-2002                            
SQL> -- To see the system default date format
SQL> -- and all four year digits:
SQL> SELECT SYSDATE,
  2           TO_CHAR (SYSDATE, 'dd-Mon-yyyy')
  3  FROM   DUAL
  4  /
SYSDATE   TO_CHAR(SYS                  
16-Jan-02 16-Jan-2002                  
SQL> -- If your table is like this
SQL> -- (using the simplified structure
SQL> --  that you sent in your e-mail):
SQL> CREATE TABLE slaughter
  2    (slaughter_no   NUMBER (12)
  3                   PRIMARY KEY,
  4       slaughter_set  VARCHAR2 (10) NOT NULL,
  5       slaughter_date DATE)
  6  /
Table created.
SQL> -- If you insert the system date
SQL> -- into your slaughter_date
SQL> INSERT INTO slaughter
  2  VALUES (1, 'test1', SYSDATE)
  3  /
1 row created.
SQL> -- You can see the default format
SQL> -- and all four year digits like this:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_no = 1
  6  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           1 16-Jan-02 16-Jan-2002     
SQL> -- You can insert using SYSDATE - number_of_days:
SQL> INSERT INTO slaughter
  2  VALUES (2, 'test2', SYSDATE-180)
  3  /
1 row created.
SQL> -- results:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_no = 2
  6  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           2 20-Jul-01 20-Jul-2001     
SQL> -- You can insert by converting a character format
SQL> -- to a date format:
SQL> INSERT INTO slaughter
  2  VALUES (3, 'test3', TO_DATE ('28-Feb-2001', 'dd-Mon-yyyy'))
  3  /
1 row created.
SQL> INSERT INTO slaughter
  2  VALUES (4, 'test4', TO_DATE ('28-Mar-2001', 'dd-Mon-yyyy'))
  3  /
1 row created.
SQL> INSERT INTO slaughter
  2  VALUES (5, 'test5', TO_DATE ('28-Feb-1998', 'dd-Mon-yyyy'))
  3  /
1 row created.
SQL> -- results:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_no IN (3, 4, 5)
  6  ORDER BY slaughter_no
  7  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           3 28-Feb-01 28-Feb-2001     
           4 28-Mar-01 28-Mar-2001     
           5 28-Feb-98 28-Feb-1998     
SQL> -- You can insert using the nls_date_format
SQL> -- and the system will automatically do an
SQL> -- implicit conversion to the date format,
SQL> -- however, if you only give it the last
SQL> -- two digits of the year, you don't know
SQL> -- if if thinks it is 1998 or 2098:
SQL> INSERT INTO slaughter
  2  VALUES (6, 'test6', '28-Feb-98')
  3  /
1 row created.
SQL> INSERT INTO slaughter
  2  VALUES (7, 'test7', '28-Feb-01')
  3  /
1 row created.
SQL> INSERT INTO slaughter
  2  VALUES (8, 'test8', '28-Mar-01')
  3  /
1 row created.
SQL> -- the results:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_no IN (6, 7, 8)
  6  ORDER BY slaughter_no
  7  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           6 28-Feb-98 28-Feb-2098     
           7 28-Feb-01 28-Feb-2001     
           8 28-Mar-01 28-Mar-2001     
SQL> -- the whole table now looks like:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  ORDER BY slaughter_no
  6  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           1 16-Jan-02 16-Jan-2002     
           2 20-Jul-01 20-Jul-2001     
           3 28-Feb-01 28-Feb-2001     
           4 28-Mar-01 28-Mar-2001     
           5 28-Feb-98 28-Feb-1998     
           6 28-Feb-98 28-Feb-2098     
           7 28-Feb-01 28-Feb-2001     
           8 28-Mar-01 28-Mar-2001     
8 rows selected.
SQL> -- One way to select slaughter_date within the last six
SQL> -- months is to use the add_months function.
SQL> -- Using -6 causes it to subtract six months
SQL> -- from the system date.  So, you are asking for
SQL> -- slaughter_date between the system date minus six months
SQL> -- and the system date:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_date BETWEEN ADD_MONTHS (SYSDATE, -6)
  6                    AND        SYSDATE
  7  ORDER BY slaughter_no
  8  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           1 16-Jan-02 16-Jan-2002     
           2 20-Jul-01 20-Jul-2001     
SQL> -- Or you can specify between certain dates,
SQL> -- using the full format, to be sure what year you
SQL> -- are asking for:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_date
  6           BETWEEN TO_DATE ('16-Jul-2001', 'dd-Mon-yyyy')
  7           AND     TO_DATE ('17-Jan-2002', 'dd-Mon-yyyy')
  8  ORDER BY slaughter_no
  9  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           1 16-Jan-02 16-Jan-2002     
           2 20-Jul-01 20-Jul-2001     
SQL> -- Using the values that you provided:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy')
  4  FROM   slaughter
  5  WHERE  slaughter_date
  6           BETWEEN TO_DATE ('28-Feb-2001', 'dd-Mon-yyyy')
  7           AND     TO_DATE ('28-Mar-2001', 'dd-Mon-yyyy')
  8  ORDER BY slaughter_no
  9  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLA     
           3 28-Feb-01 28-Feb-2001     
           4 28-Mar-01 28-Mar-2001     
           7 28-Feb-01 28-Feb-2001     
           8 28-Mar-01 28-Mar-2001     
SQL> -- Remember that if you are using the system date
SQL> -- for input or queries that it includes the time,
SQL> -- so if you are just interested in the date portion,
SQL> -- you may want to use the trunc function.  Note the
SQL> -- differences in the following queries:
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy hh24:mi')
  4  FROM   slaughter
  5  WHERE  slaughter_date BETWEEN ADD_MONTHS (SYSDATE, -6)
  6                    AND        SYSDATE
  7  ORDER BY slaughter_no
  8  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLAUGHTER
           1 16-Jan-02 16-Jan-2002 14:32
           2 20-Jul-01 20-Jul-2001 14:32
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy hh24:mi')
  4  FROM   slaughter
  5  WHERE  TRUNC (slaughter_date)
  6           BETWEEN ADD_MONTHS (SYSDATE, -6)
  7           AND     SYSDATE
  8  ORDER BY slaughter_no
  9  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLAUGHTER
           1 16-Jan-02 16-Jan-2002 14:32
           2 20-Jul-01 20-Jul-2001 14:32
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy hh24:mi')
  4  FROM   slaughter
  5  WHERE  slaughter_date
  6           BETWEEN ADD_MONTHS (TRUNC (SYSDATE), -6)
  7           AND     TRUNC (SYSDATE)
  8  ORDER BY slaughter_no
  9  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLAUGHTER
           2 20-Jul-01 20-Jul-2001 14:32
SQL> SELECT slaughter_no,
  2           slaughter_date,
  3           TO_CHAR (slaughter_date, 'dd-Mon-yyyy hh24:mi')
  4  FROM   slaughter
  5  WHERE  TRUNC (slaughter_date)
  6           BETWEEN ADD_MONTHS (TRUNC (SYSDATE), -6)
  7           AND     TRUNC (SYSDATE)
  8  ORDER BY slaughter_no
  9  /
SLAUGHTER_NO SLAUGHTER TO_CHAR(SLAUGHTER
           1 16-Jan-02 16-Jan-2002 14:32
           2 20-Jul-01 20-Jul-2001 14:32
SQL> -- The above are just a few ideas.
SQL> -- There are many different ways to do things.
SQL> --
SQL> -- One more point, regarding naming
SQL> -- your primary and foreign keys.
SQL> -- If you try to insert a duplicate value
SQL> -- that violates your primary key constraint:
SQL> INSERT INTO slaughter
  2  VALUES (1, 'test9', SYSDATE)
  3  /
INSERT INTO slaughter
ERROR at line 1:
ORA-00001: unique constraint
(SCOTT.SYS_C002996) violated
SQL> -- You get an error message that doens't
SQL> -- tell you much.     However, if you have
SQL> -- a meaningful name for you primary key
SQL> -- and you try the same thing, you get a
SQL> -- more meaningful error message:
SQL> ALTER TABLE slaughter
  2  DROP PRIMARY KEY
  3  /
Table altered.
SQL> ALTER TABLE slaughter
  2  ADD CONSTRAINT slaughter_pk
  3  PRIMARY KEY (slaughter_no)
  4  /
Table altered.
SQL> INSERT INTO slaughter
  2  VALUES (1, 'test9', SYSDATE)
  3  /
INSERT INTO slaughter
ERROR at line 1:
ORA-00001: unique constraint
(SCOTT.SLAUGHTER_PK) violated