Commits on Apr 27, 2024

1. Add rudimentary UNION support to the QueryBuilder …

   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 parentheses.
   
   Taking the shared requirements and working behaviour,
   it is possible to provide a generic support to the
   QueryBuilder with a minimalistic surface addition now,
   and following methods are added:
   
   * `union(string|QueryBuilder ...$unionParts)` and
     `addUnion(string|QueryBuilder ...$unionParts)` to
      create a `UNION` query retrieving unique rows
   * `unionAll(string|QueryBuilder ...$unionParts)` and
     `addUnionAll(string|QueryBuilder ...$unionParts) to
      create a `UNION ALL` query retrieving eventually
      duplicated rows.
   
   This follows the generic logic as `select(...)` and
   `addSelect(...)` along with introducing new internal
   `QueryType::UNION_DISTINCT` and `QueryType::UNION_ALL`
   enum cases.
   
   Additional to the consideration to allow SQL strings
   and QueryBuilder for `union()`, `unionAll(), `addUnion()`
   and `addUnionAll()` and minimize the direct handling
   of miss-configuration to the number of provided parts
   and let other issues like the field (order, count, naming)
   or not allowed order by handling to the database itself.
   With that, vendor specific implementation can be done if
   required.
   
   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.
   
   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,    /*$select11, $select12, ... */)
      ->addUnion($select20, /*$select21, $select22, ... */)
      ->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 Apr 27, 2024
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