Date Functions

This section describes the following date functions:

ADD_MONTHS
DATE_TRUNC
LAST_DAY
MONTHS_BETWEEN
SYSTIMESTAMP

ADD_MONTHS

ADD_MONTHS is an Oracle system function and is not implicitly supported by GaussDB(DWS).

Before using this function, perform the following operations:

Create and use the MIG_ORA_EXT schema.
Copy the content of the custom script and execute the script in all target databases for which migration is to be performed. For details, see Migration Process.

ADD_MONTHS returns a date with the month.

Data type of the date parameter is DATETIME.
Data type of the integer parameter is INTEGER.

The return type is DATE.

Input - ADD_MONTHS

    
         SELECT
          TO_CHAR( ADD_MONTHS ( hire_date ,1 ) ,'DD-MON-YYYY' ) "Next month"
     FROM
          employees
     WHERE
          last_name = 'Baer'
;

Output

    
         SELECT
          TO_CHAR( MIG_ORA_EXT.ADD_MONTHS ( hire_date ,1 ) ,'DD-MON-YYYY' ) "Next month"
     FROM
          employees
     WHERE
          last_name = 'Baer'
;

TO_DATE with Third Parameter

In TO_DATE(' 2019-05-02 00:00:00', 'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN'), the third parameter should be commented.

Input

   
         CREATE TABLE PRODUCT
     ( prod_id       INTEGER      
     , prod_code     VARCHAR(5)   
     , prod_name     VARCHAR(100)
     , unit_price    NUMERIC(6,2) NOT NULL
     , manufacture_date  DATE DEFAULT sysdate )
 PARTITION BY RANGE (manufacture_date)
 (PARTITION "P_20190501"  VALUES LESS THAN (TO_DATE(' 2019-05-02 00:00:00', 'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN')) 
  );

Output

   
         CREATE TABLE PRODUCT
     ( prod_id       INTEGER      
     , prod_code     VARCHAR(5)   
     , prod_name     VARCHAR(100)
     , unit_price    NUMERIC(6,2) NOT NULL
     , manufacture_date  DATE DEFAULT sysdate )
 PARTITION BY RANGE (manufacture_date)
 (PARTITION "P_20190501"  VALUES LESS THAN (TO_DATE(' 2019-05-02 00:00:00', 'YYYY-MM-DD HH24:MI:SS'/* , 'NLS_CALENDAR=GREGORIAN' */)) 
  );

DATE_TRUNC

The DATE_TRUNC function returns a date with the time portion of the day truncated to the unit specified by the format model fmt.

Input

   
        select trunc(to_char(trunc(add_months(sysdate,-12),'MM'),'YYYYMMDD')/100) into v_start_date_s from dual;
select trunc(to_char(trunc(sysdate,'mm'),'YYYYMMDD')/100) into v_end_date_e from dual;
ID_MNTH>=TRUNC(TO_CHAR(ADD_MONTHS(to_date(to_char('||v_curr_date||'),''YYYYMMDD''),-12),''YYYYMMDD'')/100))
AND ID_MNTH>=TRUNC(TO_CHAR(ADD_MONTHS(to_date(to_char('||v_curr_date||'),''YYYYMMDD''),-12),''YYYYMMDD'')/100))

select TRUNC(to_char(add_months(trunc(TO_DATE(TO_CHAR(P_DATE),'YYYYMMDD'),'MM')-1,-2),'YYYYMMDD')/100) INTO START_MONTH from dual; 
select TRUNC(TO_CHAR(trunc(TO_DATE(TO_CHAR(P_DATE),'YYYYMMDD'),'MM')-1,'YYYYMMDD')/100) INTO END_MONTH from dual;

Output

   
        SELECT Trunc(To_char(Date_trunc ('MONTH', mig_ora_ext.Add_months (SYSDATE, -12)) , 'YYYYMMDD') / 100) 
INTO   v_start_date_s 
FROM   dual; 

SELECT Trunc(To_char(Date_trunc ('MONTH', SYSDATE), 'YYYYMMDD') / 100) 
INTO   v_end_date_e 
FROM   dual; 

SELECT Trunc(To_char(mig_ora_ext.Add_months (Date_trunc ('MONTH', To_date(To_char(p_date), 'YYYYMMDD' )) - 1 , -2), 'YYYYMMDD') / 100) 
INTO   start_month 
FROM   dual;

SELECT Trunc(To_char(Date_trunc ('MONTH', To_date(To_char(p_date), 'YYYYMMDD')) - 1, 'YYYYMMDD') / 100) 
INTO   end_month 
FROM   dual;

LAST_DAY

The Oracle LAST_DAY function returns the last day of the month based on a date value.

LAST_DAY(date)

The return type is always DATE, regardless of the data type of the date.

LAST_DAY is an Oracle system function and is not implicitly supported by GaussDB(DWS). To support this function, DSC creates a LAST_DAY function in the MIG_ORA_EXT schema. The migrated statements will use the new function MIG_ORA_EXT.LAST_DAY as shown in the following example.

Before using this function, perform the following operations:

Create and use the MIG_ORA_EXT schema.
Copy the content of the custom script and execute the script in all target databases for which migration is to be performed. For details, see Migration Process.

Input - LAST_DAY

    
          SELECT
          to_date( '01/' || '07/' || to_char( sysdate ,'YYYY' ) ,'dd/mm/yyyy' ) FIRST
          ,last_day( to_date( '01/' || '07/' || to_char( sysdate ,'YYYY' ) ,'dd/mm/yyyy' ) ) last__day
   FROM
          dual;

Output

    
         SELECT
          to_date( '01/' || '07/' || to_char( sysdate ,'YYYY' ) ,'dd/mm/yyyy' ) FIRST
          ,MIG_ORA_EXT.LAST_DAY (
               to_date( '01/' || '07/' || to_char( sysdate ,'YYYY' ) ,'dd/mm/yyyy' )
          ) last__day
  FROM
          dual;

MONTHS_BETWEEN

The MONTHS_BETWEEN function returns the number of months between two dates.

MONTHS_BETWEEN is an Oracle system function and is not implicitly supported by GaussDB(DWS). To support this function, use DSC to create a MONTHS_BETWEEN function in the MIG_ORA_EXT schema. The migrated statements will use the new function MIG_ORA_EXT.MONTHS_BETWEEN as shown in the following example.

Before using this function, perform the following operations:

Create and use the MIG_ORA_EXT schema.
Copy the content of the custom script and execute the script in all the target databases to which data is to be migrated. For details, see Migration Process.

Input - MONTHS_BETWEEN

Select Months_Between(to_date('2017-06-20', 'YYYY-MM-DD'), to_date('2011-06-20', 'YYYY-MM-DD')) from dual;

Output

Select MIG_ORA_EXT.MONTHS_BETWEEN(to_date('2017-06-20', 'YYYY-MM-DD'), to_date('2011-06-20', 'YYYY-MM-DD')) from dual;

SYSTIMESTAMP

The SYSTIMESTAMP function returns the system date, including fractional seconds and time zones, of the system on which the database resides. The return type is TIMESTAMP WITH TIME ZONE.

Figure 1 Input - SYSTIMESTAMP