Commits on Jun 14, 2024

1. Add QueryBuilder support for UNION clause …

   The `UNION` operator is used to combine the result-set
   of two or more `SELECT` statements, which all database
   vendors supports with usual specialities for each.
   
   Still, there is a common shared subset which works for
   all of them:
   
   ```
       SELECT column_name(s) FROM table1
       WHERE ...
   
       UNION <ALL | DISTINCT>
   
       SELECT column_name(s) FROM table2
       WHERE ...
   
       ORDER BY ...
       LIMIT x OFFSET y
   ```
   
   with shared common requirements:
   
   * Each `SELECT` must return the same fields
     in number, naming and order.
   
   * Each `SELECT` **must not** have `ORDER BY`,
     expect MySQL allowing it to be used as sub
     query expression encapsulated in parenthesis.
   
   It is now possible to build `UNION` queries using
   following additional QueryBuilder API methods:
   
   * `union(string|QueryBuilder $part)` to create a `UNION`
      query retrieving unique rows
   * `addUnion(string|QueryBuilder $part, UnionType $type)`
      to add `UNION (ALL|DISTINCT)` query with the selected
      union query type.
   
   This follows the generic logic of `select(...)` and
   `addSelect(...)` along with introducing new UnionType
   enum and internal QueryType::UNION enum case.
   
   Technically, the SQL build process is dispatched to a
   `DefaultUnionSQLBuilder` along with an `UnionSQLBuilder`
   interface, which also allows application to implement
   custom behaviour if required. Union SQL keyword and part
   SQL generation is handled through added methods on the
   Platforms to allow adjustment for furture versions if
   needed - or throw a Exception if a Platform does not
   support it anymore.
   
   Example:
   
   ```php
   $platform = $connection->getDatabasePlatform();
   $qb       = $>connection->createQueryBuilder();
   $select10 = $platform->getDummySelectSQL('2 as field_one');
   $select20 = $platform->getDummySelectSQL('1 as field_one');
   $qb->union($select10)
      ->addUnion($select20, UnionType::ALL)
      ->setMaxResults(1)
      ->setFirstResult(1)
      ->orderBy('field_one', 'ASC');
   $rows = $qb->executeQuery()->fetchAllAssociative();
   ```
   
   Unit and functional tests are added to demonstrate the
   implementation and cover it for future changes.
   
   Resolves: doctrine#6368

   

   sbuerk committed Jun 14, 2024
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