Re: [HACKERS] Undefined psql variables

Hello Corey,

        \if defined varname
        \if sql boolean expression to send to server
        \if compare value operator value

I'm still thinking:-)

Independently of the my aethetical complaint against having a pretty
unusual keyword prefix syntax, how would you envision a \set assignment
variant? Would \if have a different expression syntax somehow?

Any further thoughts?

My current opinion:

 - I'm fine if \set stays as it is, i.e. no expression.

 - I agree that some client-side expressions are needed, along the
   semantics suggested by Tom, i.e. definition and comparisons.

 - I'm really against the prefix syntax suggested by Tom


I wish I could have an explanation about why the :?varname (or some other variant) syntax I suggested has a "namespace" issue.

The advantage that I see is that although it is obviously ugly, it is ugly in the continuity of the various :["'?]varname syntaxes already offered and it allows to get rid of "defined varname" which does not look like SQL. A second advantage is that with the "defined" proposal

   \if defined var1 and defined var2 or defined var3 and sqlrt() >= ..

Would probably never work work, as it cannot be embedded in another expression, while it would work with

   \if :?var1 and :?var2 or :?var3 and ...

Moreover, I would like the condition syntax to be basically SQL & psql variables, without explicit prefixes, with a transparent decision whether it is evaluated client side or server side.

As client-side expressions are pretty simple, ISTM that some regex could be used for this purpose, eg for integer and boolean comparisons:

 ^\s*\d+\s*(=|<>|!=|<|<=|>|>=)\s*\d+\s*$
 ^\s*(bool...)\s*(=|<>|!=)\s*(bool...)\s*$
 ^\s*(NOT\s*)?(bool...)\s*$

So that one could just write the expressions without having to tell where it is executed, eg

 \if :VERSION_NUM < 110000

Would lead to

 \if 100000 < 110000

Caught by the first regex, and evaluated with a few lines of code.

--
Fabien.

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