
Changes in SQL::Abstract 1.23

1) Large patch by Laurent Dami to add all of the
following functionality:

 - support for nested subqueries (see the doc for explanations)
 - +/- prefixes in C<@order> columns, meaning 'ASC' or 'DESC'
 - documentation :
    - added an explanation about flexibility of argument types
      (passing scalars instead of hashrefs/arrayrefs)
    - added an example of a boolean column (through ref to empty
      string)
    - mentioned that select() can take an arrayref of tables
    - added explanation of +/- prefixes in C<@order>
    - WHERE section structured into subsections
    - new subsection for nested queries
    - suppressed the NOTES section about Morgan laws, because
      subqueries provide support for compound logic statements.

These changes enable additional functionality in DBIx::DataModel
as well.

2) Patch by Robbie Bow to enable "quote_char" to take
an array ref.  This fixes an issue to MS SQL Server,
since it requires that columns and tables be quoted with
surrounding [square brackets]

3) Patch by Norbert BUCHMULLER to enable the use of
the old-school-SQL operator for not-equal ('<>')
could be used for the 'IS NOT NULL' expression:

  foo => { '<>' => undef }

This now properly generates:

  foo IS NOT NULL

