Doesn't push down comparisons to 'now()'

[davidcrawford]

Since the code only pushes down quals that compare to T_Const, T_Param, and T_Var, it doesn't evaluate now() (a T_FuncExpr) and push down as a constant. I don't know enough about PostgreSQL development to know if this would be easy or hard. I'm happy to contribute this feature if you can give me a starting point.

[rdunklau]

This is something I would really like to see happening: not treating the
T_Param specially, and using the whole expression evaluation.

Frankly, the current code to do this is quite ugly and only manages a
subset of the tree.

I'll try to look a bit deeper into it, but I think it would need the
following:

• The building of the clauses (quals list and params list) is done at plan
  time, and cached for the execution. (via the extract_restrictions
  machinery). This must change, at least for params.
• At plan time, the restrictions should be scanned again to find every
  T_Var OPERATOR AnyExpr clauses, and evaluate the right hand side (using
  ExecEvalExpr).

I don't really know what amount of work does that entail, but I'm convinced
the resulting code would be cleaner (no more awkward serialization between
plan and execution phase).

If I recall correctly, postgres_fdw does exactly that. You may look at it
for inspiration :)

2013/6/28 David Crawford notifications@github.com

Since the code only pushes down quals that compare to T_Const, T_Param,
and T_Var, it doesn't evaluate now() (a T_FuncExpr) and push down as a
constant. I don't know enough about PostgreSQL development to know if this
would be easy or hard. I'm happy to contribute this feature if you can give
me a starting point.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/18
.

[rdunklau]

I just pushed this to the master branch:

• params are no longer treated specially
• every expression on the right hand side which does not contain any volatile function (such as random) or a reference to the table itself (ie, col1 = some_function(col2)) will be evaluated at execution time.