Re: [Sqlalchemy-tickets] [sqlalchemy] #2843: Support for IF EXISTS/IF NOT EXISTS DDL constructs

[sqlalchemy <mi...@zz...>]

#2843: Support for IF EXISTS/IF NOT EXISTS DDL constructs
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      Reporter:  remyroy      |      Owner:  zzzeek
          Type:  enhancement  |     Status:  new
      Priority:  medium       |  Milestone:  0.9.xx
     Component:  schema       |   Severity:  major - 1-3 hours
    Resolution:               |   Keywords:
Progress State:  in queue     |
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Comment (by remyroy):

 Would it make sense to merge the currently implemented checkfirst logic
 with the IF EXISTS/IF NOT EXISTS implementation? What I mean is that for
 dialects who supports IF EXISTS/IF NOT EXISTS for a specific object type,
 no introspection would be done whenever checkfirst=True, only the CREATE
 or DROP statement would be issued with the proper IF EXISTS/IF NOT EXISTS
 vocabulary. That would save some roundtrip to the database for those who
 support IF EXISTS/IF NOT EXISTS.

 I would also rename "checkfirst" to "checkexists" and update the
 documentation accordingly.

 Would it be a good idea to include a long list of supports_[statement |
 "[create|drop]_[object type]" ]_checkexists attributes for each dialect
 class? I believe some DBMS have mixed IF EXISTS/IF NOT EXISTS support for
 different object types and for CREATE or DROP and other statements. For
 instance, PostgreSQL 8.2 supports DROP TABLE IF EXISTS but does not
 support CREATE TABLE IF NOT EXISTS or ALTER TABLE DROP COLUMN IF EXISTS
 while PostgreSQL 9.2 supports DROP TABLE IF EXISTS, CREATE TABLE IF NOT
 EXISTS and ALTER TABLE DROP COLUMN IF EXISTS.

 I might be able to work on this and get you a pull request with
 documentation and tests.

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2843#comment:3>
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