#24638: New feature: support adding an SQL comment in queries
-------------------------------------+-------------------------------------
Reporter: adamchainz | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 1.8
(models, ORM) |
Severity: Normal | Resolution:
Keywords: queryset, query, | Triage Stage: Accepted
comment, optimizer hint |
Has patch: 1 | Needs documentation: 1
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by adamchainz):
For reference (checking I did get the right place for Oracle and MySQL
query hints):
1. MySQL hints are listed in its syntax
https://dev.mysql.com/doc/refman/5.5/en/select.html (STRAIGHT_JOIN,
SQL_NO_CACHE, etc.). They can be inserted as comments by starting the
comment with an exclamation mark, which pretty much means "this is not a
comment" (the reason this exists is that if you follow the exclamation
mark with an encoded version number, that SQL will only be executed on
versions of the server at that version or above). Also newer more powerful
hints are coming in 5.7 with comments that start with a + :
https://dev.mysql.com/worklog/task/?id=8017
2. Oracle has extensive documentation on its hints which appear only in
conditional comments, although the page is lacking in examples:
http://docs.oracle.com/cd/B19306_01/server.102/b14211/hintsref.htm .
However the syntax for SELECT does show hints going *before* DISTINCT:
http://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_10002.htm
, however this blog post shows them after: http://www.dba-
oracle.com/t_index_fast_full_scan.htm .
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Ticket URL: <https://code.djangoproject.com/ticket/24638#comment:5>
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