tailieunhanh - Oracle Built−in Packages- P91

Oracle Built−in Packages- P91: Ah, for the good old days of Version of PL /SQL! Life was so simple then. No stored procedures or functions and certainly no packages. You had your set of built−in functions, like SUBSTR and TO_DATE. You had the IF statement and various kinds of loops. With these tools at hand, you built your batch−processing scripts for execution in SQL*Plus, and you coded your triggers in SQL*Forms , and you went home at night content with a good day's work done. | Appendix A What s on the Companion Disk Restrictions Note the following restrictions on calling ROWID_TO_EXTENDED The ROWID_TO_EXTENDED function returns a ROWID in the extended character format. If you provide a NULL ROWID the function will return NULL. If a zero-valued ROWID is supplied a zero-valued restricted ROWID is returned. The DBMS_ROWID package supplies the following pragma for ROWID_TO_EXTENDED PRAGMA RESTRICT_REFERENCES ROWID_TO_EXTENDED WNDS WNPS RNPS If the schema and object names are provided as IN parameters this function first verifies that you have SELECT privilege on the table named. It then converts the restricted ROWID provided to an extended ROWID using the data object number of the specified table. Even if ROWID_TO_EXTENDED returns a value however that does not guarantee that the converted ROWID actually references a valid row in the table either at the time that the function is called or when the extended ROWID is actually used. It is only performing a conversion. If the schema and object name are not provided . are passed as NULL then this function attempts to fetch the page specified by the restricted ROWID provided. It treats the file number stored in this ROWID as the absolute file number. This may cause problems if the file has been dropped and its number has been reused prior to the data migration. If the fetched page belongs to a valid table the data object number of this table is used in converting to an extended ROWID value. This approach is very inefficient. Oracle recommends doing this only as a last resort when the target table is not known. Note that the user must still be aware of the correct table name when using the converted ROWID. If an extended ROWID value is supplied that ROWID s data object is verified against the data object number calculated from the table name argument. If the two numbers do not match DBMS_ROWID raises the INVALID_ROWID exception. If there is a match then the input .