From 7b29866e4b411b1f4c074175215e5c2b3d9e43dd Mon Sep 17 00:00:00 2001
From: Andrey Pyzhikov <5071@mail.ru>
Date: Tue, 16 Feb 2021 06:12:19 +0800
Subject: [PATCH 1/5] New: BaseBuilder. Added methods that implement UNION.

---
 system/Database/BaseBuilder.php               | 142 +++++++++++++--
 tests/system/Database/Builder/UnionTest.php   | 171 ++++++++++++++++++
 .../source/database/query_builder.rst         |  94 ++++++++++
 3 files changed, 396 insertions(+), 11 deletions(-)
 create mode 100644 tests/system/Database/Builder/UnionTest.php

diff --git a/system/Database/BaseBuilder.php b/system/Database/BaseBuilder.php
index 610fe8e54528..53a7dcdb9f98 100644
--- a/system/Database/BaseBuilder.php
+++ b/system/Database/BaseBuilder.php
@@ -139,6 +139,20 @@ class BaseBuilder
 	 */
 	protected $QBWhereGroupCount = 0;
 
+	/**
+	 * Collection of union queries
+	 *
+	 * @var string[]
+	 */
+	protected $QBUnion = [];
+
+	/**
+	 * UNION ORDER BY data
+	 *
+	 * @var array
+	 */
+	protected $QBUnionOrderBy = [];
+
 	/**
 	 * Ignore data that cause certain
 	 * exceptions, for example in case of
@@ -3022,7 +3036,14 @@ protected function compileSelect($selectOverride = false): string
 		// LIMIT
 		if ($this->QBLimit)
 		{
-			return $this->_limit($sql . "\n");
+			$sql = $this->_limit($sql . "\n");
+		}
+
+		if ($this->QBUnion)
+		{
+			$sql = '(' . $sql . ')'
+				. $this->compileUnion()
+				. $this->compileUnionOrderBy();
 		}
 
 		return $sql;
@@ -3358,16 +3379,18 @@ protected function resetRun(array $qbResetItems)
 	protected function resetSelect()
 	{
 		$this->resetRun([
-			'QBSelect'   => [],
-			'QBJoin'     => [],
-			'QBWhere'    => [],
-			'QBGroupBy'  => [],
-			'QBHaving'   => [],
-			'QBOrderBy'  => [],
-			'QBNoEscape' => [],
-			'QBDistinct' => false,
-			'QBLimit'    => false,
-			'QBOffset'   => false,
+			'QBSelect'       => [],
+			'QBJoin'         => [],
+			'QBWhere'        => [],
+			'QBGroupBy'      => [],
+			'QBHaving'       => [],
+			'QBOrderBy'      => [],
+			'QBNoEscape'     => [],
+			'QBUnion'        => [],
+			'QBUnionOrderBy' => [],
+			'QBDistinct'     => false,
+			'QBLimit'        => false,
+			'QBOffset'       => false,
 		]);
 
 		if (! empty($this->db))
@@ -3492,6 +3515,103 @@ protected function setBind(string $key, $value = null, bool $escape = true): str
 		return $key . $count;
 	}
 
+	/**
+	 * Union queries
+	 *
+	 * @param Closure $closure Contains a query to combine
+	 *
+	 * @return static
+	 */
+	public function union(Closure $closure)
+	{
+		return $this->unionBuilder($closure);
+	}
+
+	/**
+	 * Union queries
+	 *
+	 * @param Closure $closure Contains a query to combine
+	 *
+	 * @return static
+	 */
+	public function unionAll(Closure $closure)
+	{
+		return $this->unionBuilder($closure, true);
+	}
+
+	/**
+	 * Union query builder
+	 *
+	 * @param Closure $closure Contains a query to combine
+	 * @param boolean $all     Using UNION ALL construction
+	 *
+	 * @return static
+	 */
+	protected function unionBuilder(Closure $closure, bool $all = false)
+	{
+		$builder = $closure($this->cleanClone());
+
+		if (! ($builder instanceof BaseBuilder))
+		{
+			throw new DatabaseException(
+				'BaseBuilder::union(). The closure must return an instance of the BaseBuilder class'
+			);
+		}
+		$sql = $builder->getCompiledSelect();
+
+		$all = $all ? 'ALL ' : '';
+
+		$this->QBUnion[] = ' UNION ' . $all . '(' . $sql . ')';
+
+		return $this;
+	}
+
+	/**
+	 * Compile UNION queries
+	 *
+	 * @return string
+	 */
+	protected function compileUnion() : string
+	{
+		return count($this->QBUnion) ? join('', $this->QBUnion) : '';
+	}
+
+	/**
+	 * ORDER BY
+	 *
+	 * @param string  $orderBy   Field
+	 * @param string  $direction ASC, DESC or RANDOM
+	 * @param boolean $escape    Escape
+	 *
+	 * @return static
+	 */
+	public function unionOrderBy(string $orderBy, string $direction = '', bool $escape = null)
+	{
+		$this->QBUnionOrderBy[] = [
+			$orderBy,
+			$direction,
+			$escape,
+		];
+
+		return $this;
+	}
+
+	/**
+	 * Compile UNION ORDER BY data
+	 *
+	 * @return string
+	 */
+	protected function compileUnionOrderBy() : string
+	{
+		$builder = $this->cleanClone();
+		foreach ($this->QBUnionOrderBy as $order)
+		{
+			$builder->orderBy(...$order);
+		}
+
+		return $builder->compileOrderBy();
+	}
+
 	//--------------------------------------------------------------------
 
 	/**
diff --git a/tests/system/Database/Builder/UnionTest.php b/tests/system/Database/Builder/UnionTest.php
new file mode 100644
index 000000000000..52c97104cf97
--- /dev/null
+++ b/tests/system/Database/Builder/UnionTest.php
@@ -0,0 +1,171 @@
+<?php namespace CodeIgniter\Database\Builder;
+
+use CodeIgniter\Database\BaseBuilder;
+use CodeIgniter\Database\Exceptions\DatabaseException;
+use CodeIgniter\Test\Mock\MockConnection;
+
+class UnionTest extends \CodeIgniter\Test\CIUnitTestCase
+{
+	protected $db;
+
+	//--------------------------------------------------------------------
+
+	protected function setUp(): void
+	{
+		parent::setUp();
+
+		$this->db = new MockConnection([]);
+	}
+
+	public function testUnion()
+	{
+		$builder = $this->db->table('movies');
+
+		$builder->select('title, year')
+			->union(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('top_movies');
+			});
+
+		$sql = '(SELECT "title", "year" FROM "movies") UNION (SELECT "title", "year" FROM "top_movies")';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+	}
+
+	public function testUnionExceptions()
+	{
+		$builder = $this->db->table('movies');
+		$builder->select('title, year');
+
+		$this->expectException(\TypeError::class);
+
+		$builder->union(1);
+
+		$this->expectException(DatabaseException::class);
+		$this->expectExceptionMessage(
+			'BaseBuilder::union(). The closure must return an instance of the BaseBuilder class'
+		);
+
+		$builder->union(function (BaseBuilder $builder) {
+			$builder->select('title, year')->from('top_movies');
+		});
+	}
+
+	public function testUnionAll()
+	{
+		$builder = $this->db->table('movies');
+
+		$builder->select('title, year')
+			->unionAll(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('top_movies');
+			});
+
+		$sql = '(SELECT "title", "year" FROM "movies") UNION ALL (SELECT "title", "year" FROM "top_movies")';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+	}
+
+	public function testMultiQueryUnion()
+	{
+		$builder = $this->db->table('movies');
+
+		$builder->select('title, year')
+			->union(function (BaseBuilder $builder) {
+				return $builder->select('title, year')
+					->from('top_movies')
+					->unionAll(function (BaseBuilder $builder) {
+						return $builder->select('title, year')->from('tomato_movies');
+					});
+			});
+
+		$sql = '(SELECT "title", "year" FROM "movies") '
+				. 'UNION ((SELECT "title", "year" FROM "top_movies") '
+					. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies"))';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+
+		$builder->resetQuery();
+
+		$builder->select('title, year')
+			->union(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('top_movies');
+			})->unionAll(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('tomato_movies');
+			});
+
+		$sql = '(SELECT "title", "year" FROM "movies") '
+				. 'UNION (SELECT "title", "year" FROM "top_movies") '
+				. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies")';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+
+		$builder->resetQuery();
+
+		$year1 = 2000;
+		$year2 = 2010;
+		$year3 = 2020;
+
+		$builder->select('title, year')
+			->where('year', $year1)
+			->union(function (BaseBuilder $builder) use ($year2, $year3) {
+				return $builder->select('title, year')
+					->from('top_movies')
+					->where('year', $year2)
+					->unionAll(function (BaseBuilder $builder) use ($year3) {
+						return $builder->select('title, year')
+							->from('tomato_movies')
+							->where('year', $year3);
+					});
+			});
+
+		$sql = '(SELECT "title", "year" FROM "movies" WHERE "year" = 2000) '
+			. 'UNION ((SELECT "title", "year" FROM "top_movies" WHERE "year" = 2010) '
+			. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies" WHERE "year" = 2020))';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+	}
+
+	public function testUnionOrderBy()
+	{
+		$builder = $this->db->table('movies');
+
+		$builder->select('title, year')
+			->unionAll(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('top_movies');
+			})
+			->unionOrderBy('title', 'DESC')
+			->unionOrderBy('year', 'ASC');
+
+		$sql = '(SELECT "title", "year" FROM "movies") '
+			. 'UNION ALL (SELECT "title", "year" FROM "top_movies") ORDER BY "title" DESC, "year" ASC';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+
+		$builder->resetQuery();
+
+		$builder->select('title, year')
+			->union(function (BaseBuilder $builder) {
+				return $builder->select('title, year')
+					->from('top_movies')
+					->unionAll(function (BaseBuilder $builder) {
+						return $builder->select('title, year')->from('tomato_movies');
+					})->unionOrderBy('title', 'DESC');
+			});
+
+		$sql = '(SELECT "title", "year" FROM "movies") '
+			. 'UNION ((SELECT "title", "year" FROM "top_movies") '
+			. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies") ORDER BY "title" DESC)';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+	}
+
+	public function testIgnoreUnionOrderByWithoutUnionQuery()
+	{
+		$builder = $this->db->table('movies');
+
+		$builder->select('title, year')->unionOrderBy('year', 'ASC');
+
+		$sql = 'SELECT "title", "year" FROM "movies"';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+	}
+}
diff --git a/user_guide_src/source/database/query_builder.rst b/user_guide_src/source/database/query_builder.rst
index e0fb96c8d68f..df28955fb1ac 100755
--- a/user_guide_src/source/database/query_builder.rst
+++ b/user_guide_src/source/database/query_builder.rst
@@ -839,6 +839,100 @@ Starts a new group by adding an opening parenthesis to the HAVING clause of the
 
 Ends the current group by adding a closing parenthesis to the HAVING clause of the query.
 
+*************************
+Combining queries (UNION)
+*************************
+
+.. note:: To understand how UNION works, it is recommended to study the documentation for the used DBMS.
+
+**$builder->union()**
+
+The method combines the results of several queries into one common one and takes a Closure as an argument.
+The Closure must return an instance of the BaseBuilder class::
+
+    //Add the following line after the namespace keyword
+    use CodeIgniter\Database\BaseBuilder;
+
+    $builder = $db->table('movies');
+
+    $builder->select('title, year')
+        ->union(function (BaseBuilder $builder) {
+            return $builder->select('title, year')->from('top_movies');
+        })
+        ->get();
+
+    // (SELECT title, year FROM movies) UNION (SELECT title, year FROM top_movies)
+
+Nested UNION and variable passing::
+
+    //Add the following line after the namespace keyword
+    use CodeIgniter\Database\BaseBuilder;
+
+    $year = 2000;
+    $yearTop = 2010;
+    $yearBad = 2020;
+
+    $builder = $db->table('movies');
+
+    $builder->select('title, year')
+        ->where('year', $year)
+        ->union(function (BaseBuilder $builder) use ($yearTop, $yearBad){
+            return $builder->select('title, year')
+                ->from('top_movies')
+                ->where('year', $yearTop)
+                ->union(function (BaseBuilder $builder) use ($yearBad){
+                    return $builder->select('title, year')
+                        ->from('bad_movies')
+                        ->where('year', $yearBad)
+                });
+        })
+        ->get();
+
+    // (SELECT title, year FROM movies WHERE year = 2000)
+    //  UNION (
+    //      (SELECT title, year FROM top_movies WHERE year = 2010)
+    //      UNION (SELECT title, year FROM bad_movies WHERE year = 2020)
+    //  )
+
+
+**$builder->unionAll()**
+
+The method adds ALL to UNION::
+
+    //Add the following line after the namespace keyword
+    use CodeIgniter\Database\BaseBuilder;
+
+    $builder = $db->table('movies');
+
+    $builder->select('title, year')
+        ->unionAll(function (BaseBuilder $builder) {
+            return $builder->select('title, year')->from('top_movies');
+        })
+        ->get();
+
+    // (SELECT title, year FROM movies) UNION ALL (SELECT title, year FROM top_movies)
+
+
+**$builder->unionOrderBy()**
+
+The method adds a sort for the final query result after combining queries using UNION [ALL].
+The principle is the same as for ``orderBy()``::
+
+    //Add the following line after the namespace keyword
+    use CodeIgniter\Database\BaseBuilder;
+
+    $builder = $db->table('movies');
+
+    $builder->select('title, year')
+        ->unionAll(function (BaseBuilder $builder) {
+            return $builder->select('title, year')->from('top_movies');
+        })
+        ->unionOrderBy('title', 'DESC')
+        ->get();
+
+    // (SELECT title, year FROM movies) UNION ALL (SELECT title, year FROM top_movies) ORDER BY title DESC
+
+
 **************
 Inserting Data
 **************

From 4ddf1d800afb4e211217ea055ac8ad8f32edc387 Mon Sep 17 00:00:00 2001
From: Andrey Pyzhikov <5071@mail.ru>
Date: Wed, 17 Feb 2021 12:57:58 +0800
Subject: [PATCH 2/5] New: BaseBuilder. Added methods that implement UNION.
 LiveTest

---
 system/Database/BaseBuilder.php               | 22 ++++-
 system/Database/SQLSRV/Builder.php            | 12 ++-
 tests/system/Database/Builder/UnionTest.php   | 96 ++++++-------------
 tests/system/Database/Live/UnionTest.php      | 39 ++++++++
 .../source/database/query_builder.rst         | 45 ++-------
 5 files changed, 106 insertions(+), 108 deletions(-)
 create mode 100644 tests/system/Database/Live/UnionTest.php

diff --git a/system/Database/BaseBuilder.php b/system/Database/BaseBuilder.php
index 53a7dcdb9f98..463c4b5fc404 100644
--- a/system/Database/BaseBuilder.php
+++ b/system/Database/BaseBuilder.php
@@ -3041,9 +3041,12 @@ protected function compileSelect($selectOverride = false): string
 
 		if ($this->QBUnion)
 		{
-			$sql = '(' . $sql . ')'
-				. $this->compileUnion()
-				. $this->compileUnionOrderBy();
+			if ($this->QBOrderBy || $this->QBLimit)
+			{
+				$sql = 'SELECT * FROM (' . $sql . ') as wrapper_alias';
+			}
+
+			$sql .= $this->compileUnion() . $this->compileUnionOrderBy();
 		}
 
 		return $sql;
@@ -3557,11 +3560,20 @@ protected function unionBuilder(Closure $closure, bool $all = false)
 				'BaseBuilder::union(). The closure must return an instance of the BaseBuilder class'
 			);
 		}
-		$sql = $builder->getCompiledSelect();
+
+		$sql = $builder->getCompiledSelect(false);
 
 		$all = $all ? 'ALL ' : '';
 
-		$this->QBUnion[] = ' UNION ' . $all . '(' . $sql . ')';
+		if (($builder->QBOrderBy || $builder->QBLimit || $builder->QBUnionOrderBy)
+			&& strpos($sql, 'wrapper_alias UNION') === false)
+		{
+			$sql = 'SELECT * FROM (' . $sql . ') as wrapper_alias';
+		}
+
+		$builder->resetSelect();
+
+		$this->QBUnion[] = ' UNION ' . $all . $sql;
 
 		return $this;
 	}
diff --git a/system/Database/SQLSRV/Builder.php b/system/Database/SQLSRV/Builder.php
index af914bf26f59..6fdf7e7ea856 100755
--- a/system/Database/SQLSRV/Builder.php
+++ b/system/Database/SQLSRV/Builder.php
@@ -651,7 +651,17 @@ protected function compileSelect($selectOverride = false): string
 		// LIMIT
 		if ($this->QBLimit)
 		{
-			return $sql = $this->_limit($sql . "\n");
+			$sql = $this->_limit($sql . "\n");
+		}
+
+		if ($this->QBUnion)
+		{
+			if ($this->QBOrderBy || $this->QBLimit)
+			{
+				$sql = 'SELECT * FROM (' . $sql . ') as wrapper_alias';
+			}
+
+			$sql .= $this->compileUnion() . $this->compileUnionOrderBy();
 		}
 
 		return $sql;
diff --git a/tests/system/Database/Builder/UnionTest.php b/tests/system/Database/Builder/UnionTest.php
index 52c97104cf97..fabc677b48a7 100644
--- a/tests/system/Database/Builder/UnionTest.php
+++ b/tests/system/Database/Builder/UnionTest.php
@@ -22,11 +22,13 @@ public function testUnion()
 		$builder = $this->db->table('movies');
 
 		$builder->select('title, year')
+			->orderBy('title')
 			->union(function (BaseBuilder $builder) {
 				return $builder->select('title, year')->from('top_movies');
 			});
 
-		$sql = '(SELECT "title", "year" FROM "movies") UNION (SELECT "title", "year" FROM "top_movies")';
+		$sql = 'SELECT * FROM (SELECT "title", "year" FROM "movies" ORDER BY "title") as wrapper_alias '
+			. 'UNION SELECT "title", "year" FROM "top_movies"';
 
 		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
 	}
@@ -55,71 +57,15 @@ public function testUnionAll()
 		$builder = $this->db->table('movies');
 
 		$builder->select('title, year')
+			->orderBy('title')
 			->unionAll(function (BaseBuilder $builder) {
-				return $builder->select('title, year')->from('top_movies');
-			});
-
-		$sql = '(SELECT "title", "year" FROM "movies") UNION ALL (SELECT "title", "year" FROM "top_movies")';
-
-		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
-	}
-
-	public function testMultiQueryUnion()
-	{
-		$builder = $this->db->table('movies');
-
-		$builder->select('title, year')
-			->union(function (BaseBuilder $builder) {
 				return $builder->select('title, year')
 					->from('top_movies')
-					->unionAll(function (BaseBuilder $builder) {
-						return $builder->select('title, year')->from('tomato_movies');
-					});
-			});
-
-		$sql = '(SELECT "title", "year" FROM "movies") '
-				. 'UNION ((SELECT "title", "year" FROM "top_movies") '
-					. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies"))';
-
-		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
-
-		$builder->resetQuery();
-
-		$builder->select('title, year')
-			->union(function (BaseBuilder $builder) {
-				return $builder->select('title, year')->from('top_movies');
-			})->unionAll(function (BaseBuilder $builder) {
-				return $builder->select('title, year')->from('tomato_movies');
+					->orderBy('title');
 			});
 
-		$sql = '(SELECT "title", "year" FROM "movies") '
-				. 'UNION (SELECT "title", "year" FROM "top_movies") '
-				. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies")';
-
-		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
-
-		$builder->resetQuery();
-
-		$year1 = 2000;
-		$year2 = 2010;
-		$year3 = 2020;
-
-		$builder->select('title, year')
-			->where('year', $year1)
-			->union(function (BaseBuilder $builder) use ($year2, $year3) {
-				return $builder->select('title, year')
-					->from('top_movies')
-					->where('year', $year2)
-					->unionAll(function (BaseBuilder $builder) use ($year3) {
-						return $builder->select('title, year')
-							->from('tomato_movies')
-							->where('year', $year3);
-					});
-			});
-
-		$sql = '(SELECT "title", "year" FROM "movies" WHERE "year" = 2000) '
-			. 'UNION ((SELECT "title", "year" FROM "top_movies" WHERE "year" = 2010) '
-			. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies" WHERE "year" = 2020))';
+		$sql = 'SELECT * FROM (SELECT "title", "year" FROM "movies" ORDER BY "title") as wrapper_alias '
+			. 'UNION ALL SELECT * FROM (SELECT "title", "year" FROM "top_movies" ORDER BY "title") as wrapper_alias';
 
 		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
 	}
@@ -135,8 +81,8 @@ public function testUnionOrderBy()
 			->unionOrderBy('title', 'DESC')
 			->unionOrderBy('year', 'ASC');
 
-		$sql = '(SELECT "title", "year" FROM "movies") '
-			. 'UNION ALL (SELECT "title", "year" FROM "top_movies") ORDER BY "title" DESC, "year" ASC';
+		$sql = 'SELECT "title", "year" FROM "movies" '
+			. 'UNION ALL SELECT "title", "year" FROM "top_movies" ORDER BY "title" DESC, "year" ASC';
 
 		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
 
@@ -149,11 +95,27 @@ public function testUnionOrderBy()
 					->unionAll(function (BaseBuilder $builder) {
 						return $builder->select('title, year')->from('tomato_movies');
 					})->unionOrderBy('title', 'DESC');
-			});
+			})->unionOrderBy('title');
+
+		$sql = 'SELECT "title", "year" FROM "movies" '
+			. 'UNION SELECT * FROM (SELECT "title", "year" FROM "top_movies" '
+			. 'UNION ALL SELECT "title", "year" FROM "tomato_movies" ORDER BY "title" DESC) as wrapper_alias ORDER BY "title"';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+
+		$builder->select('title, year')
+			->union(function (BaseBuilder $builder) {
+				return $builder->select('title, year')
+					->from('top_movies')
+					->unionAll(function (BaseBuilder $builder) {
+						return $builder->select('title, year')->from('tomato_movies');
+					})->limit(1);
+			})
+			->unionOrderBy('title');
 
-		$sql = '(SELECT "title", "year" FROM "movies") '
-			. 'UNION ((SELECT "title", "year" FROM "top_movies") '
-			. 'UNION ALL (SELECT "title", "year" FROM "tomato_movies") ORDER BY "title" DESC)';
+		$sql = 'SELECT "title", "year" FROM "movies" '
+			. 'UNION SELECT * FROM (SELECT "title", "year" FROM "top_movies"  LIMIT 1) as wrapper_alias '
+			. 'UNION ALL SELECT "title", "year" FROM "tomato_movies" ORDER BY "title"';
 
 		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
 	}
diff --git a/tests/system/Database/Live/UnionTest.php b/tests/system/Database/Live/UnionTest.php
new file mode 100644
index 000000000000..7d3588a423b0
--- /dev/null
+++ b/tests/system/Database/Live/UnionTest.php
@@ -0,0 +1,39 @@
+<?php namespace CodeIgniter\Database\Live;
+
+use CodeIgniter\Database\BaseBuilder;
+use CodeIgniter\Test\CIDatabaseTestCase;
+
+/**
+ * @group DatabaseLive
+ */
+class UnionTest extends CIDatabaseTestCase
+{
+	protected $refresh = true;
+
+	protected $seed = 'Tests\Support\Database\Seeds\CITestSeeder';
+
+	//--------------------------------------------------------------------
+
+	public function testUnion()
+	{
+		$rows = $this->db->table('user')
+			->select('name')
+			->where('country', 'US')
+			->limit(1)
+			->orderBy('name', 'DESC')
+			->union(function (BaseBuilder $builder) {
+				return $builder->select('name')
+					->from('job')
+					->where('id >', 1)
+					->limit(2);
+			})
+			->unionOrderBy('name')
+			->get()
+			->getResult();
+
+		$this->assertEquals(3, count($rows));
+		$this->assertEquals('Accountant', $rows[0]->name);
+		$this->assertEquals('Politician', $rows[1]->name);
+		$this->assertEquals('Richard A Causey', $rows[2]->name);
+	}
+}
diff --git a/user_guide_src/source/database/query_builder.rst b/user_guide_src/source/database/query_builder.rst
index df28955fb1ac..4f6d32297205 100755
--- a/user_guide_src/source/database/query_builder.rst
+++ b/user_guide_src/source/database/query_builder.rst
@@ -844,6 +844,8 @@ Combining queries (UNION)
 *************************
 
 .. note:: To understand how UNION works, it is recommended to study the documentation for the used DBMS.
+.. note:: Each separate query containing LIMIT and ORDER BY will be wrapped in a
+``SELECT * FROM (...) as wrapper_alias`` so that the DBMS will process queries correctly
 
 **$builder->union()**
 
@@ -857,42 +859,14 @@ The Closure must return an instance of the BaseBuilder class::
 
     $builder->select('title, year')
         ->union(function (BaseBuilder $builder) {
-            return $builder->select('title, year')->from('top_movies');
-        })
-        ->get();
-
-    // (SELECT title, year FROM movies) UNION (SELECT title, year FROM top_movies)
-
-Nested UNION and variable passing::
-
-    //Add the following line after the namespace keyword
-    use CodeIgniter\Database\BaseBuilder;
-
-    $year = 2000;
-    $yearTop = 2010;
-    $yearBad = 2020;
-
-    $builder = $db->table('movies');
-
-    $builder->select('title, year')
-        ->where('year', $year)
-        ->union(function (BaseBuilder $builder) use ($yearTop, $yearBad){
             return $builder->select('title, year')
-                ->from('top_movies')
-                ->where('year', $yearTop)
-                ->union(function (BaseBuilder $builder) use ($yearBad){
-                    return $builder->select('title, year')
-                        ->from('bad_movies')
-                        ->where('year', $yearBad)
-                });
+            ->from('top_movies')
+            ->orderBy('title');
         })
         ->get();
 
-    // (SELECT title, year FROM movies WHERE year = 2000)
-    //  UNION (
-    //      (SELECT title, year FROM top_movies WHERE year = 2010)
-    //      UNION (SELECT title, year FROM bad_movies WHERE year = 2020)
-    //  )
+    // SELECT title, year FROM movies
+    // UNION SELECT * FROM (SELECT title, year FROM top_movies ORDER BY title) as wrapper_alias
 
 
 **$builder->unionAll()**
@@ -905,12 +879,14 @@ The method adds ALL to UNION::
     $builder = $db->table('movies');
 
     $builder->select('title, year')
+        ->limit(1)
         ->unionAll(function (BaseBuilder $builder) {
             return $builder->select('title, year')->from('top_movies');
         })
         ->get();
 
-    // (SELECT title, year FROM movies) UNION ALL (SELECT title, year FROM top_movies)
+    // SELECT * FROM (SELECT title, year FROM movies LIMIT 1) as wrapper_alias
+    // UNION ALL SELECT title, year FROM top_movies
 
 
 **$builder->unionOrderBy()**
@@ -930,8 +906,7 @@ The principle is the same as for ``orderBy()``::
         ->unionOrderBy('title', 'DESC')
         ->get();
 
-    // (SELECT title, year FROM movies) UNION ALL (SELECT title, year FROM top_movies) ORDER BY title DESC
-
+    // SELECT title, year FROM movies UNION ALL SELECT title, year FROM top_movies ORDER BY title DESC
 
 **************
 Inserting Data

From 12e99d4d056c33c864b663d4b7fb4b1e3f660a56 Mon Sep 17 00:00:00 2001
From: Andrey Pyzhikov <5071@mail.ru>
Date: Wed, 17 Feb 2021 14:35:59 +0800
Subject: [PATCH 3/5] UG Explicit markup ends without a blank line

---
 user_guide_src/source/database/query_builder.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/user_guide_src/source/database/query_builder.rst b/user_guide_src/source/database/query_builder.rst
index 4f6d32297205..906d5f4918c6 100755
--- a/user_guide_src/source/database/query_builder.rst
+++ b/user_guide_src/source/database/query_builder.rst
@@ -845,7 +845,8 @@ Combining queries (UNION)
 
 .. note:: To understand how UNION works, it is recommended to study the documentation for the used DBMS.
 .. note:: Each separate query containing LIMIT and ORDER BY will be wrapped in a
-``SELECT * FROM (...) as wrapper_alias`` so that the DBMS will process queries correctly
+``SELECT * FROM (...) as wrapper_alias`` so that the DBMS will process queries correctly.
+
 
 **$builder->union()**
 

From b55b8a67a8b2f8076df51087c142b57c659c578f Mon Sep 17 00:00:00 2001
From: Andrey Pyzhikov <5071@mail.ru>
Date: Tue, 23 Feb 2021 15:27:54 +0800
Subject: [PATCH 4/5] Change: Changed behavior when using union and limit or
 orderBy methods

---
 system/Database/BaseBuilder.php               | 89 +++++++++++++++++--
 system/Database/SQLSRV/Builder.php            |  2 +-
 tests/system/Database/Builder/UnionTest.php   | 44 ++++++---
 .../source/database/query_builder.rst         | 22 +----
 4 files changed, 119 insertions(+), 38 deletions(-)

diff --git a/system/Database/BaseBuilder.php b/system/Database/BaseBuilder.php
index 463c4b5fc404..c9fba948eb3c 100644
--- a/system/Database/BaseBuilder.php
+++ b/system/Database/BaseBuilder.php
@@ -153,6 +153,20 @@ class BaseBuilder
 	 */
 	protected $QBUnionOrderBy = [];
 
+	/**
+	 * QB UNION LIMIT data
+	 *
+	 * @var integer|boolean
+	 */
+	protected $QBUnionLimit = false;
+
+	/**
+	 * QB UNION OFFSET data
+	 *
+	 * @var integer|boolean
+	 */
+	protected $QBUnionOffset = false;
+
 	/**
 	 * Ignore data that cause certain
 	 * exceptions, for example in case of
@@ -1634,6 +1648,11 @@ public function orHaving($key, $value = null, bool $escape = null)
 	 */
 	public function orderBy(string $orderBy, string $direction = '', bool $escape = null)
 	{
+		if (count($this->QBUnion))
+		{
+			return $this->unionOrderBy($orderBy, $direction, $escape);
+		}
+
 		$direction = strtoupper(trim($direction));
 
 		if ($direction === 'RANDOM')
@@ -1700,6 +1719,11 @@ public function orderBy(string $orderBy, string $direction = '', bool $escape =
 	 */
 	public function limit(?int $value = null, ?int $offset = 0)
 	{
+		if (count($this->QBUnion))
+		{
+			return $this->unionLimit($value, $offset);
+		}
+
 		if (! is_null($value))
 		{
 			$this->QBLimit = $value;
@@ -3039,14 +3063,14 @@ protected function compileSelect($selectOverride = false): string
 			$sql = $this->_limit($sql . "\n");
 		}
 
-		if ($this->QBUnion)
+		if (count($this->QBUnion))
 		{
 			if ($this->QBOrderBy || $this->QBLimit)
 			{
 				$sql = 'SELECT * FROM (' . $sql . ') as wrapper_alias';
 			}
 
-			$sql .= $this->compileUnion() . $this->compileUnionOrderBy();
+			$sql .= $this->compileUnion() . $this->compileUnionFilter();
 		}
 
 		return $sql;
@@ -3394,6 +3418,8 @@ protected function resetSelect()
 			'QBDistinct'     => false,
 			'QBLimit'        => false,
 			'QBOffset'       => false,
+			'QBUnionLimit'   => false,
+			'QBUnionOffset'  => false,
 		]);
 
 		if (! empty($this->db))
@@ -3565,7 +3591,7 @@ protected function unionBuilder(Closure $closure, bool $all = false)
 
 		$all = $all ? 'ALL ' : '';
 
-		if (($builder->QBOrderBy || $builder->QBLimit || $builder->QBUnionOrderBy)
+		if (($builder->QBOrderBy || $builder->QBLimit || $builder->QBUnionOrderBy || $builder->QBUnionLimit)
 			&& strpos($sql, 'wrapper_alias UNION') === false)
 		{
 			$sql = 'SELECT * FROM (' . $sql . ') as wrapper_alias';
@@ -3589,15 +3615,15 @@ protected function compileUnion() : string
 	}
 
 	/**
-	 * ORDER BY
+	 * UNION ORDER BY global
 	 *
 	 * @param string  $orderBy   Field
 	 * @param string  $direction ASC, DESC or RANDOM
 	 * @param boolean $escape    Escape
 	 *
-	 * @return static
+	 * @return $this
 	 */
-	public function unionOrderBy(string $orderBy, string $direction = '', bool $escape = null)
+	protected function unionOrderBy(string $orderBy, string $direction = '', bool $escape = null)
 	{
 		$this->QBUnionOrderBy[] = [
 			$orderBy,
@@ -3609,19 +3635,64 @@ public function unionOrderBy(string $orderBy, string $direction = '', bool $esca
 	}
 
 	/**
-	 * Compile UNION ORDER BY data
+	 * UNION LIMIT global
+	 *
+	 * @param integer|null $value  LIMIT value
+	 * @param integer|null $offset OFFSET value
+	 *
+	 * @return $this
+	 */
+	protected function unionLimit(?int $value = null, ?int $offset = 0)
+	{
+		if (! is_null($value))
+		{
+			$this->QBUnionLimit = $value;
+		}
+
+		return $this->unionOffset($offset);
+	}
+
+	/**
+	 * Sets the UNION OFFSET value
+	 *
+	 * @param integer $offset OFFSET value
+	 *
+	 * @return $this
+	 */
+	protected function unionOffset(int $offset)
+	{
+		if (! empty($offset))
+		{
+			$this->QBUnionOffset = (int) $offset;
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Compile UNION Filter as ORDER BY and LIMIT
 	 *
 	 * @return string
 	 */
-	protected function compileUnionOrderBy() : string
+	protected function compileUnionFilter() : string
 	{
 		$builder = $this->cleanClone();
+
 		foreach ($this->QBUnionOrderBy as $order)
 		{
 			$builder->orderBy(...$order);
 		}
 
-		return $builder->compileOrderBy();
+		$filter = $builder->compileOrderBy();
+
+		$builder->limit($this->QBUnionLimit, $this->QBUnionOffset);
+
+		if ($this->QBUnionLimit)
+		{
+			$filter = $builder->_limit($filter . "\n");
+		}
+
+		return $filter;
 	}
 
 	//--------------------------------------------------------------------
diff --git a/system/Database/SQLSRV/Builder.php b/system/Database/SQLSRV/Builder.php
index 6fdf7e7ea856..5cc80c6bdb55 100755
--- a/system/Database/SQLSRV/Builder.php
+++ b/system/Database/SQLSRV/Builder.php
@@ -661,7 +661,7 @@ protected function compileSelect($selectOverride = false): string
 				$sql = 'SELECT * FROM (' . $sql . ') as wrapper_alias';
 			}
 
-			$sql .= $this->compileUnion() . $this->compileUnionOrderBy();
+			$sql .= $this->compileUnion() . $this->compileUnionFilter();
 		}
 
 		return $sql;
diff --git a/tests/system/Database/Builder/UnionTest.php b/tests/system/Database/Builder/UnionTest.php
index fabc677b48a7..429c90f2d779 100644
--- a/tests/system/Database/Builder/UnionTest.php
+++ b/tests/system/Database/Builder/UnionTest.php
@@ -2,6 +2,7 @@
 
 use CodeIgniter\Database\BaseBuilder;
 use CodeIgniter\Database\Exceptions\DatabaseException;
+use CodeIgniter\Database\SQLSRV\Builder as BuilderSQLSRV;
 use CodeIgniter\Test\Mock\MockConnection;
 
 class UnionTest extends \CodeIgniter\Test\CIUnitTestCase
@@ -78,8 +79,8 @@ public function testUnionOrderBy()
 			->unionAll(function (BaseBuilder $builder) {
 				return $builder->select('title, year')->from('top_movies');
 			})
-			->unionOrderBy('title', 'DESC')
-			->unionOrderBy('year', 'ASC');
+			->orderBy('title', 'DESC')
+			->orderBy('year', 'ASC');
 
 		$sql = 'SELECT "title", "year" FROM "movies" '
 			. 'UNION ALL SELECT "title", "year" FROM "top_movies" ORDER BY "title" DESC, "year" ASC';
@@ -94,8 +95,8 @@ public function testUnionOrderBy()
 					->from('top_movies')
 					->unionAll(function (BaseBuilder $builder) {
 						return $builder->select('title, year')->from('tomato_movies');
-					})->unionOrderBy('title', 'DESC');
-			})->unionOrderBy('title');
+					})->orderBy('title', 'DESC');
+			})->orderBy('title');
 
 		$sql = 'SELECT "title", "year" FROM "movies" '
 			. 'UNION SELECT * FROM (SELECT "title", "year" FROM "top_movies" '
@@ -111,22 +112,45 @@ public function testUnionOrderBy()
 						return $builder->select('title, year')->from('tomato_movies');
 					})->limit(1);
 			})
-			->unionOrderBy('title');
+			->orderBy('title');
 
 		$sql = 'SELECT "title", "year" FROM "movies" '
-			. 'UNION SELECT * FROM (SELECT "title", "year" FROM "top_movies"  LIMIT 1) as wrapper_alias '
-			. 'UNION ALL SELECT "title", "year" FROM "tomato_movies" ORDER BY "title"';
+			. 'UNION SELECT * FROM (SELECT "title", "year" FROM "top_movies" '
+			. 'UNION ALL SELECT "title", "year" FROM "tomato_movies"  LIMIT 1) as wrapper_alias ORDER BY "title"';
 
 		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
 	}
 
-	public function testIgnoreUnionOrderByWithoutUnionQuery()
+	public function testUnionLimit()
 	{
 		$builder = $this->db->table('movies');
 
-		$builder->select('title, year')->unionOrderBy('year', 'ASC');
+		$builder->select('title, year')
+			->unionAll(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('top_movies');
+			})
+			->limit(5, 10);
+
+		$sql = 'SELECT "title", "year" FROM "movies" '
+			. 'UNION ALL SELECT "title", "year" FROM "top_movies"  LIMIT 10, 5';
+
+		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
+	}
+
+	public function testUnionSQLSRV()
+	{
+		$dbc     = new MockConnection(['schema' => 'dbo', 'database' => 'test']);
+		$builder = new BuilderSQLSRV('movies', $dbc);
+
+		$builder->select('title, year')
+			->unionAll(function (BaseBuilder $builder) {
+				return $builder->select('title, year')->from('top_movies');
+			})
+			->limit(5, 10);
 
-		$sql = 'SELECT "title", "year" FROM "movies"';
+		$sql = 'SELECT "title", "year" FROM "test"."dbo"."movies" '
+			. 'UNION ALL SELECT "title", "year" FROM "test"."dbo"."top_movies" '
+			. ' ORDER BY (SELECT NULL)  OFFSET 10 ROWS FETCH NEXT 5 ROWS ONLY ';
 
 		$this->assertEquals($sql, str_replace("\n", ' ', $builder->getCompiledSelect()));
 	}
diff --git a/user_guide_src/source/database/query_builder.rst b/user_guide_src/source/database/query_builder.rst
index 906d5f4918c6..474efd089015 100755
--- a/user_guide_src/source/database/query_builder.rst
+++ b/user_guide_src/source/database/query_builder.rst
@@ -727,6 +727,9 @@ be ignored, unless you specify a numeric seed value.
 .. note:: Random ordering is not currently supported in Oracle and
     will default to ASC instead.
 
+.. note:: The orderBy() method called after the union()/unionAll() method will be applied to the final result
+
+
 ****************************
 Limiting or Counting Results
 ****************************
@@ -745,6 +748,7 @@ The second parameter lets you set a result offset.
     $builder->limit(10, 20);
     // Produces: LIMIT 20, 10 (in MySQL. Other databases have slightly different syntax)
 
+.. note:: The limit() method called after the union()/unionAll() method will be applied to the final result
 
 **$builder->countAllResults()**
 
@@ -890,24 +894,6 @@ The method adds ALL to UNION::
     // UNION ALL SELECT title, year FROM top_movies
 
 
-**$builder->unionOrderBy()**
-
-The method adds a sort for the final query result after combining queries using UNION [ALL].
-The principle is the same as for ``orderBy()``::
-
-    //Add the following line after the namespace keyword
-    use CodeIgniter\Database\BaseBuilder;
-
-    $builder = $db->table('movies');
-
-    $builder->select('title, year')
-        ->unionAll(function (BaseBuilder $builder) {
-            return $builder->select('title, year')->from('top_movies');
-        })
-        ->unionOrderBy('title', 'DESC')
-        ->get();
-
-    // SELECT title, year FROM movies UNION ALL SELECT title, year FROM top_movies ORDER BY title DESC
 
 **************
 Inserting Data

From b31cf02573857a69ab52370496ea780ce2cd4e81 Mon Sep 17 00:00:00 2001
From: Andrey Pyzhikov <5071@mail.ru>
Date: Tue, 23 Feb 2021 15:56:21 +0800
Subject: [PATCH 5/5] Fix live test

---
 tests/system/Database/Live/UnionTest.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/system/Database/Live/UnionTest.php b/tests/system/Database/Live/UnionTest.php
index 7d3588a423b0..1bd382fa477a 100644
--- a/tests/system/Database/Live/UnionTest.php
+++ b/tests/system/Database/Live/UnionTest.php
@@ -27,7 +27,7 @@ public function testUnion()
 					->where('id >', 1)
 					->limit(2);
 			})
-			->unionOrderBy('name')
+			->orderBy('name')
 			->get()
 			->getResult();