Feature: Subquery for SELECT

Signed-off-by: Andrey Pyzhikov <5071@mail.ru>

system/Database/BaseBuilder.php

@@ -445,6 +445,22 @@ class BaseBuilder
         return $this->maxMinAvgSum($select, $alias, 'COUNT');
     }
 
+    /**
+     * Adds a subquery to the selection
+     *
+     * @return static
+     */
+    public function selectSubquery(BaseBuilder $subquery, string $as)
+    {
+        if (! $this->isSubquery($subquery)) {
+            throw new DatabaseException('The BaseBuilder::selectSubquery method expects a BaseBuilder instance');
+        }
+
+        $this->QBSelect[] = $this->buildSubquery($subquery, true, $as);
+
+        return $this;
+    }
+
     /**
      * SELECT [MAX|MIN|AVG|SUM|COUNT]()
      *

tests/system/Database/Builder/SelectTest.php

@@ -246,4 +246,17 @@ final class SelectTest extends CIUnitTestCase
 
         $this->assertSame($expected, str_replace("\n", ' ', $builder->getCompiledSelect()));
     }
+
+    public function testSelectSubquery()
+    {
+        $builder  = new BaseBuilder('users', $this->db);
+        $subquery = new BaseBuilder('countries', $this->db);
+
+        $subquery->select('name')->where('id', 1);
+        $builder->select('name')->selectSubquery($subquery, 'country');
+
+        $expected = 'SELECT "name", (SELECT "name" FROM "countries" WHERE "id" = 1) AS "country" FROM "users"';
+
+        $this->assertSame($expected, str_replace("\n", ' ', $builder->getCompiledSelect()));
+    }
 }

user_guide_src/source/changelogs/v4.2.0.rst

@@ -24,6 +24,7 @@ Enhancements
     - See :ref:`content-security-policy` for details.
 - New View Decorators allow modifying the generated HTML prior to caching.
 - Added Subqueries in the FROM section. See :ref:`query-builder-from-subquery`.
+- Added Subqueries in the SELECT section.
 - Added Validation Strict Rules. See :ref:`validation-traditional-and-strict-rules`.
 - Added new OCI8 driver for database.
     - It can access Oracle Database and supports SQL and PL/SQL statements.

user_guide_src/source/database/query_builder.rst

@@ -167,6 +167,13 @@ the resulting field.
 .. literalinclude:: query_builder/014.php
    :lines: 2-
 
+**$builder->selectSubquery()**
+
+Adds a subquery to the SELECT section.
+
+.. literalinclude:: query_builder/098.php
+   :lines: 2-
+
 From
 ====
 
@@ -1066,6 +1073,15 @@ Class Reference
 
         Adds a ``SELECT COUNT(field)`` clause to a query.
 
+.. php:method:: selectSubquery(BaseBuilder $subquery, string $as)
+
+        :param string $subquery: Instance of BaseBuilder
+        :param string $as: Alias for the resulting value name
+        :returns:   ``BaseBuilder`` instance (method chaining)
+        :rtype:     ``BaseBuilder``
+
+        Adds a subquery to the selection
+
     .. php:method:: distinct([$val = true])
 
         :param bool $val: Desired value of the "distinct" flag

user_guide_src/source/database/query_builder/098.php

@@ -0,0 +1,7 @@
+<?php
+
+$subquery = $db->table('countries')->select('name')->where('id', 1);
+$builder  = $db->table('users')->select('name')->selectSubquery($subquery, 'country');
+$query = $builder->get();
+
+// Produces: SELECT `name`, (SELECT `name` FROM `countries` WHERE `id` = 1) AS `country` FROM `users`