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Thursday, November 10, 2011

Joined Criteria for an Oracle Delete

This post contains an example of deleting from an Oracle table restricted to records defined in a subquery

The FROM argument to an oracle DELETE statement can be a subquery as well as the more common table.

  SELECT * FROM tbl_j j
  JOIN tbl_a a ON (a.a_id = j.a_id)
  JOIN tbl_b b ON (b.b_id = j.b_id)
  WHERE a.a_name = 'A RECORD'
  AND b.b_name = 'B_RECORD'

tbl_a and tbl_b are tables with a name column: a_name and b_name.  These tables are related by a join table, tbl_j bu their IDs: a_id and b_id.  The following are the schemas for the table.

tbl_a ( a_id, a_name, .... )
tbl_b (b_id, b_name, ... )
tbl_j (a_id, b_id )

If the logic surround the deletion is too complex, this can be moved to a PL/SQL block that iterates over the candidate records and issues a DELETE using only a WHERE clause

DELETE FROM tbl_j WHERE a_id = ? AND b_id = ?

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