1  ERASE
   Erases records from a relation. Before using the ERASE statement,
   you must start a read/write transaction and establish a record
   stream using a context variable with a FOR statement or a START_
   STREAM statement. You cannot erase records from a view that was
   formed with a WITH, REDUCED, or CROSS clause of an RDO record
   selection expression. Also, you cannot erase records from a view
   that was formed with a UNION clause of an SQL select expression.

   Example:

   RDO> START_TRANSACTION READ_WRITE RESERVING
   cont>  COLLEGES FOR EXCLUSIVE WRITE
   RDO>     FOR C IN COLLEGES
   cont>      ERASE C
   cont>    END_FOR
   RDO> COMMIT
 

2  Format

 (B)0ERASE q> context-var qwqqqqqqq>qqqqqwq>
                       mq> on-error qj

 

3  context-var
   A temporary name specified in an RSE for name recognition. You
   must define the context variable in a START_STREAM statement or
   in a FOR loop. Request HELP on RSE for more information.
 

3  on-error
   The ON ERROR clause, which specifies a host language statement or
   Oracle Rdb data manipulation statement to be performed if an Oracle Rdb
   error occurs. Request HELP on ON_ERROR for more information.
 

2  More
   You need the Oracle Rdb READ and ERASE privileges to the relation
   and the Oracle Rdb ERASE privilege to the database to use the ERASE
   statement.

   You cannot erase records from a view that was formed with one of
   the following clauses:

   o  WITH clause of an RDO record selection expression

   o  REDUCED TO clause of an RDO record selection expression

   o  CROSS clause of an RDO record selection expression

   o  UNION clause of an SQL select expression

   Prior to Version 4.1, Oracle Rdb allowed you to erase rows from a
   table that was directly joined with other tables. Beginning with
   Version 4.1, Oracle Rdb returns an error message if you try to erase
   a row under these conditions. For example, Oracle Rdb will return
   the error, $RDMS-E-JOIN_CTX_UPD, relation EMPLOYEES is part of
   a join, cannot be updated, when you try to execute the following
   query:

   FOR E IN EMPLOYEES CROSS D IN DEGREES OVER EMPLOYEE_ID
       WITH D.DEGREE= 'MA'
       ERASE E
   END_FOR

   In the preceding query, if an employee has two MA degrees, the
   same employee row will be joined to two different degree rows.
   Therefore, Oracle Rdb will try to delete the same row twice. The
   previous update query can be reworded into an equivalent form to
   achieve the desired results as follows:

   FOR E IN EMPLOYEES WITH
      (ANY D IN DEGREES WITH D.EMPLOYEE_ID = E.EMPLOYEE_ID)
      ERASE E
   END_FOR

   The rows can now be erased because the EMPLOYEES table is no
   longer directly joined to the DEGREES table. The use of this
   query guarantees that an employee row will not be deleted more
   than once.

   Note that some examples in the Guide to Using RDO, RDBPRE, and
   RDML will no longer work with the update rules created in Oracle Rdb
   Version 4.1. To run these examples, rewrite them using the ANY
   subquery mentioned previously.
 

2  Examples
   Example 1

   Assume you wish to erase all the records in the COLLEGES
   relation:

   RDO> START_TRANSACTION READ_WRITE RESERVING
   cont>  COLLEGES FOR EXCLUSIVE WRITE
   RDO> FOR C IN COLLEGES ERASE C END-FOR
   RDO> PRINT COUNT OF C IN COLLEGES
    0
   RDO> COMMIT

   This statement uses the loop established by the FOR statement and
   erases all the records from the COLLEGES relation.