NAME

DBIx::SQLEngine::Driver::Trait::NoUnions - For databases without select unions

SYNOPSIS

  # Classes can import this behavior if they don't have native unions
  use DBIx::SQLEngine::Driver::Trait::NoUnions ':all';
  
  # Implements a workaround for unavailable sql_union capability
  $rows = $sqldb->fetch_select_rows( union => [
    { table => 'foo', columns => '*' },
    { table => 'bar', columns => '*' },
  ] );

DESCRIPTION

This package supports SQL database servers which do natively provide a SQL select with unions. Instead, queries with unions are executed separately and their results combined.

About Driver Traits

You do not need to use this package directly; it is used internally by those driver subclasses which need it.

Note: this feature has been added recently, and the interface is subject to change.

Note: Because of the way DBIx::AnyDBD munges the inheritance tree, DBIx::SQLEngine subclasses can not reliably inherit from this package. To work around this, we export all of the methods into their namespace using Exporter and @EXPORT.

In addition we go through some effort to re-dispatch methods because we can't rely on SUPER and we don't want to require NEXT. This isn't too complicated, as we know the munged inheritance tree only uses single inheritance. See the source code for the _super_dispatch function that handles this.

REFERENCE

The following methods are provided:

Database Capability Information

dbms_union_unsupported()

  $sqldb->dbms_union_unsupported() : 1

Capability Limitation: This driver does not support native select unions.

Select to Retrieve Data

fetch_select()

  $sqldb->fetch_select( %sql_clauses ) : $row_hashes
  $sqldb->fetch_select( %sql_clauses ) : ($row_hashes,$column_hashes)

Unless passed a "union" argument pair, simply calls the superclass method. Runs each of the provided queries separately and concatenates their results. Munges the keys used to turn rows into hashes, so that all results use the column names produced by the first of the queries.

fetch_select_rows()

  $sqldb->fetch_select_rows( %sql_clauses ) : $row_arrays
  $sqldb->fetch_select_rows( %sql_clauses ) : ($row_arrays,$column_hashes)

Unless passed a "union" argument pair, simply calls the superclass method. Runs each of the provided queries separately and concatenates their results.

visit_select()

  $sqldb->visit_select( $code_ref, %sql_clauses ) : @results
  $sqldb->visit_select( %sql_clauses, $code_ref ) : @results

Unless passed a "union" argument pair, simply calls the superclass method. Runs each of the provided queries separately and concatenates their results.

To Do: This method doesn't yet munge the column names retrived by the later queries to match the first.

visit_select_rows()

  $sqldb->visit_select_rows( $code_ref, %sql_clauses ) : @results
  $sqldb->visit_select_rows( %sql_clauses, $code_ref ) : @results

Unless passed a "union" argument pair, simply calls the superclass method. Runs each of the provided queries separately and concatenates their results.

sql_union()

Calls Carp::confess().

SEE ALSO

See DBIx::SQLEngine for the overall interface and developer documentation.

See DBIx::SQLEngine::Docs::ReadMe for general information about this distribution, including installation and license information.