Gavin Sherry <swm(at)linuxworld(dot)com(dot)au> writes:
> I haven't had time to look into it further, but it occurs to me that
> handling views which rely on joins would be far from trivial.
Views containing joins would not be updatable; problem solved. The set
of views the automatic-rule-generation machinery needs to handle are
those defined as updatable by the SQL spec. SQL92 says
12)A <query specification> QS is updatable if and only if the fol-
lowing conditions hold:
a) QS does not specify DISTINCT.
b) Every <value expression> contained in the <select list> imme-
diately contained in QS consists of a <column reference>, and
no <column reference> appears more than once.
c) The <from clause> immediately contained in the <table ex-
pression> immediately contained in QS specifies exactly one
<table reference> and that <table reference> refers either to
a base table or to an updatable derived table.
Note: updatable derived table is defined in Subclause 6.3,
d) If the <table expression> immediately contained in QS imme-
diately contains a <where clause> WC, then no leaf generally
underlying table of QS shall be a generally underlying table
of any <query expression> contained in WC.
e) The <table expression> immediately contained in QS does not
include a <group by clause> or a <having clause>.
The reference to 6.3 appears to be pointing at this:
8) A <derived table> is an updatable derived table if and only if
the <query expression> simply contained in the <subquery> of the
<table subquery> of the <derived table> is updatable.
I haven't quite wrapped my head around what clause 12d means, but 12c is
perfectly clear that you only get one table reference.
regards, tom lane
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