NEW Add sql UNION abstraction

src/ORM/Connect/DBQueryBuilder.php

@@ -68,13 +68,23 @@ public function buildSQL(SQLExpression $query, &$parameters)
      */
     protected function buildSelectQuery(SQLSelect $query, array &$parameters)
     {
-        $sql  = $this->buildSelectFragment($query, $parameters);
+        $needsParenthisis = count($query->getUnions()) > 0;
+        $newLine = $this->getSeparator();
+        $sql = '';
+        if ($needsParenthisis) {
+            $sql .= "({$newLine}";
+        }
+        $sql .= $this->buildSelectFragment($query, $parameters);
         $sql .= $this->buildFromFragment($query, $parameters);
         $sql .= $this->buildWhereFragment($query, $parameters);
         $sql .= $this->buildGroupByFragment($query, $parameters);
         $sql .= $this->buildHavingFragment($query, $parameters);
         $sql .= $this->buildOrderByFragment($query, $parameters);
         $sql .= $this->buildLimitFragment($query, $parameters);
+        if ($needsParenthisis) {
+            $sql .= "{$newLine})";
+        }
+        $sql .= $this->buildUnionFragment($query, $parameters);
         return $sql;
     }
 
@@ -269,6 +279,37 @@ public function buildWhereFragment(SQLConditionalExpression $query, array &$para
         return "{$nl}WHERE (" . implode("){$nl}{$connective} (", $where) . ")";
     }
 
+    /**
+     * Return the UNION clause(s) ready for inserting into a query.
+     */
+    protected function buildUnionFragment(SQLSelect $query, array &$parameters): string
+    {
+        $unions = $query->getUnions();
+        if (empty($unions)) {
+            return '';
+        }
+
+        $nl = $this->getSeparator();
+        $clauses = [];
+
+        foreach ($unions as $union) {
+            $unionQuery = $union['query'];
+            $unionType = $union['type'];
+
+            $clause = "{$nl}UNION";
+
+            if ($unionType) {
+                $clause .= " $unionType";
+            }
+
+            $clause .= "$nl($nl" . $this->buildSelectQuery($unionQuery, $parameters) . "$nl)";
+
+            $clauses[] = $clause;
+        }
+
+        return implode('', $clauses);
+    }
+
     /**
      * Returns the ORDER BY clauses ready for inserting into a query.
      *

src/ORM/DataQuery.php

@@ -655,6 +655,20 @@ public function having($having)
         return $this;
     }
 
+    /**
+     * Add a query to UNION with.
+     *
+     * @param string|null $type One of the SQLSelect::UNION_ALL or SQLSelect::UNION_DISTINCT constants - or null for a default union
+     */
+    public function union(self|SQLSelect $query, ?string $type = null): static
+    {
+        if ($query instanceof self) {
+            $query = $query->query();
+        }
+        $this->query->addUnion($query, $type);
+        return $this;
+    }
+
     /**
      * Create a disjunctive subgroup.
      *

src/ORM/Queries/SQLSelect.php

@@ -5,13 +5,17 @@
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\ORM\DB;
 use InvalidArgumentException;
+use LogicException;
 
 /**
  * Object representing a SQL SELECT query.
  * The various parts of the SQL query can be manipulated individually.
  */
 class SQLSelect extends SQLConditionalExpression
 {
+    public const UNION_ALL = 'ALL';
+
+    public const UNION_DISTINCT = 'DISTINCT';
 
     /**
      * An array of SELECT fields, keyed by an optional alias.
@@ -36,6 +40,11 @@ class SQLSelect extends SQLConditionalExpression
      */
     protected $having = [];
 
+    /**
+     * An array of subqueries to union with this one.
+     */
+    protected array $union = [];
+
     /**
      * If this is true DISTINCT will be added to the SQL.
      *
@@ -529,6 +538,29 @@ public function getHavingParameterised(&$parameters)
         return $conditions;
     }
 
+    /**
+     * Add a select query to UNION with.
+     *
+     * @param string|null $type One of the UNION_ALL or UNION_DISTINCT constants - or null for a default union
+     */
+    public function addUnion(self $query, ?string $type = null): static
+    {
+        if ($type && $type !== self::UNION_ALL && $type !== self::UNION_DISTINCT) {
+            throw new LogicException('Union $type must be one of the constants UNION_ALL or UNION_DISTINCT.');
+        }
+
+        $this->union[] = ['query' => $query, 'type' => $type];
+        return $this;
+    }
+
+    /**
+     * Get all of the queries that will be UNIONed with this one.
+     */
+    public function getUnions(): array
+    {
+        return $this->union;
+    }
+
     /**
      * Return a list of GROUP BY clauses used internally.
      *

tests/php/ORM/SQLSelectTest.php

@@ -9,6 +9,7 @@
 use SilverStripe\SQLite\SQLite3Database;
 use SilverStripe\PostgreSQL\PostgreSQLDatabase;
 use SilverStripe\Dev\SapphireTest;
+use SilverStripe\ORM\ArrayList;
 
 class SQLSelectTest extends SapphireTest
 {
@@ -791,6 +792,46 @@ public function testParameterisedLeftJoins()
         $query->execute();
     }
 
+    public function provideUnion()
+    {
+        return [
+            [
+                'unionQuery' => new SQLSelect([1, 2]),
+                'type' => null,
+                'expected' => [
+                    [1 => 1, 2 => 2],
+                ],
+            ],
+            [
+                'unionQuery' => new SQLSelect([3, 4]),
+                'type' => SQLSelect::UNION_DISTINCT,
+                'expected' => [
+                    [1 => 1, 2 => 2],
+                    [1 => 3, 2 => 4],
+                ],
+            ],
+            [
+                'unionQuery' => new SQLSelect([1, 2]),
+                'type' => SQLSelect::UNION_ALL,
+                'expected' => [
+                    [1 => 1, 2 => 2],
+                    [1 => 1, 2 => 2],
+                ],
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider provideUnion
+     */
+    public function testUnion(SQLSelect $unionQuery, ?string $type, array $expected)
+    {
+        $query = new SQLSelect([1, 2]);
+        $query->addUnion($unionQuery, $type);
+
+        $this->assertSame($expected, iterator_to_array($query->execute(), true));
+    }
+
     public function testBaseTableAliases()
     {
         $query = SQLSelect::create('*', ['"MyTableAlias"' => '"MyTable"']);