Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 12 ■ DATATYPES 531 DT TS -------------------- -------------------------------- 28-jun-2005 10:45:20 28-JUN-05 10.45.20.744866000 AM ops$tkyte@ORA10G> select dump(ts,16) dump from t; DUMP -------------------------------------------------- Typ=180 Len=11: 78,69,6,1c,b,2e,15,2c,65,c0,d0 ops$tkyte@ORA10G> select to_number('2c65c0d0','xxxxxxxx') from dual; TO_NUMBER('2C65C0D0','XXXXXXXX') -------------------------------- 744866000 We can see the fractional seconds that were stored are there in the last 4 bytes. We used the DUMP function to inspect the data in HEX this time (base 16) so we could easily convert the 4 bytes into the decimal representation. Adding Time to or Subtracting Time from a TIMESTAMP The same techniques we applied to DATE for date arithmetic work with a TIMESTAMP, but the TIMESTAMP will be converted into a DATE in many cases using the preceding techniques, for example: ops$tkyte@ORA10G> alter session set nls_date_format = 'dd-mon-yyyy hh24:mi:ss'; Session altered. ops$tkyte@ORA10G> select systimestamp ts, systimestamp+1 dt 2 from dual; TS DT ------------------------------------ -------------------- 28-JUN-05 11.04.49.833097 AM -04:00 29-jun-2005 11:04:49 Note that adding 1 did, in fact, advance the SYSTIMESTAMP by a day, but the fractional seconds are gone, as would be the time zone information. This is where using INTERVALs will be more important: ops$tkyte@ORA10G> select systimestamp ts, systimestamp +numtodsinterval(1,'day') dt 2 from dual; TS DT ------------------------------------ ---------------------------------------- 28-JUN-05 11.08.03.958866 AM -04:00 29-JUN-05 11.08.03.958866000 AM -04:00 Using the function that returns an INTERVAL type preserved the fidelity of the TIMESTAMP. You will need to exercise caution when using TIMESTAMPs, to avoid the implicit conversions.
532 CHAPTER 12 ■ DATATYPES But bear in mind the caveat about adding intervals of months or years to a TIMESTAMP. If the resulting day isn’t a valid date, the operation fails (adding one month to the last day in January will always fail if the month is added via an INTERVAL). Getting the Difference Between Two TIMESTAMPs This is where the DATE and TIMESTAMP types diverge significantly. Whereas the results of subtracting a DATE from a DATE was a NUMBER, the result of doing the same to a TIMESTAMP is an INTERVAL: ops$tkyte@ORA10G> select dt2-dt1 2 from (select to_timestamp('29-feb-2000 01:02:03.122000', 3 'dd-mon-yyyy hh24:mi:ss.ff') dt1, 4 to_timestamp('15-mar-2001 11:22:33.000000', 5 'dd-mon-yyyy hh24:mi:ss.ff') dt2 6 from dual ) 7 / DT2-DT1 --------------------------------------------------------------------------- +000000380 10:20:29.878000000 The difference between two TIMESTAMP values is an INTERVAL, and this shows us the number of days and hours/minutes/seconds between the two. If we desire to have the years, months, and so forth, we are back to using a query similar to the one we used with dates: ops$tkyte@ORA10G> select numtoyminterval 2 (months_between(dt2,dt1),'month') 3 years_months, 4 dt2-add_months(dt1,trunc(months_between(dt2,dt1))) 5 days_hours 6 from (select to_timestamp('29-feb-2000 01:02:03.122000', 7 'dd-mon-yyyy hh24:mi:ss.ff') dt1, 8 to_timestamp('15-mar-2001 11:22:33.000000', 9 'dd-mon-yyyy hh24:mi:ss.ff') dt2 10 from dual ) 11 / YEARS_MONTHS DAYS_HOURS ------------- ----------------------------- +000000001-00 +000000015 10:20:30.000000000 Note in this case, since we used ADD_MONTHS, DT1 was converted implicitly into a DATE type and we lost the fractional seconds. We would have to add yet more code to preserve them. We could use NUMTOYMINTERVAL to add the months and preserve the TIMESTAMP; however, we would be subject to runtime errors:
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Expert Oracle Database Architecture
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Contents Foreword . . . . . . . . .
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■CONTENTS v Block Buffer Cache .
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■CONTENTS vii ■CHAPTER 9 Redo a
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■CONTENTS ix ■CHAPTER 12 Dataty
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Foreword “THINK.” In 1914, Thom
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■FOREWORD xiii Tom is an aficiona
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About the Technical Reviewers ■JO
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Introduction The inspiration for th
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■INTRODUCTION xix • Exposure to
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■INTRODUCTION xxi Chapter 3: File
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■INTRODUCTION xxiii Next up are t
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Setting Up Your Environment In this
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■SETTING UP YOUR ENVIRONMENT xxvi
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■SETTING UP YOUR ENVIRONMENT xlii
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CHAPTER 1 ■ ■ ■ Developing Su
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CHAPTER 1 ■ DEVELOPING SUCCESSFUL
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CHAPTER 3 ■ FILES 89 A Brief Revi
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CHAPTER 3 ■ FILES 95 dictionary t
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CHAPTER 4 ■ MEMORY STRUCTURES 117
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CHAPTER 5 ■ ORACLE PROCESSES 157
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CHAPTER 8 ■ ■ ■ Transactions
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284 CHAPTER 9 ■ REDO AND UNDO cri
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338 CHAPTER 10 ■ DATABASE TABLES
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CHAPTER 11 ■ ■ ■ Indexes Inde
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CHAPTER 11 ■ INDEXES 423 value of
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CHAPTER 11 ■ INDEXES 445 Indicate
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706 ■INDEX autonomous transaction
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Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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