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+Query Builder and Query
+=======================
+
+Yii provides a basic database access layer as was described in [Database basics](database-basics.md) section. Still it's
+a bit too much to use SQL directly all the time. To solve the issue Yii provides a query builder that allows you to
+work with the database in object-oriented style.
+
+Basic query builder usage is the following:
+
+```php
+$query = new Query;
+
+// Define query
+$query->select('id, name')
+ 	->from('tbl_user')
+ 	->limit(10);
+
+// Create a command. You can get the actual SQL using $command->sql
+$command = $query->createCommand();
+// Execute command
+$rows = $command->queryAll();
+```
+
+Basic selects and joins
+-----------------------
+
+In order to form a `SELECT` query you need to specify what to select and where to select it from.
+
+```php
+$query->select('id, name')
+	->from('tbl_user');
+```
+
+If you want to get IDs of all users with posts you can use `DISTINCT`. With query builder it will look like the following:
+
+```php
+$query->select('user_id')->distinct()->from('tbl_post');
+```
+
+Select options can be specified as array. It's especially useful when these are formed dynamically.
+
+```php
+$query->select(array('tbl_user.name AS author', 'tbl_post.title as title')) // <-- specified as array
+	->from('tbl_user')
+	->leftJoin('tbl_post', 'tbl_post.user_id = tbl_user.id'); // <-- join with another table
+```
+
+In the code above we've used `leftJoin` method to select from two related tables at the same time. Firsrt parameter
+specifies table name and the second is the join condition. Query builder has the following methods to join tables:
+
+- `innerJoin`
+- `leftJoin`
+- `rightJoin`
+
+If your data storage supports more types you can use generic `join` method:
+
+```php
+$query->join('FULL OUTER JOIN', 'tbl_post', 'tbl_post.user_id = tbl_user.id');
+```
+
+Specifying conditions
+---------------------
+
+Usually you need data that matches some conditions. There are some useful methods to specify these and the most powerful
+is `where`. There are multiple ways to use it.
+
+The simplest is to specify condition in a string:
+
+```php
+$query->where('status=:status', array(
+	':status' => $status,
+));
+```
+
+When using this format make sure you're binding parameters and not creating a query by string concatenation.
+
+Instead of binding status value immediately you can do it using `params` or `addParams`:
+
+```php
+$query->where('status=:status');
+
+$query->addParams(array(
+	':status' => $status,
+));
+```
+
+There is another convenient way to use the method called hash format:
+
+```php
+$query->where(array(
+	'status' => 10,
+	'type' => 2,
+	'id' => array(4, 8, 15, 16, 23, 42),
+));
+```
+
+It will generate the following SQL:
+
+```sql
+WHERE (`status` = 10) AND (`type` = 2) AND (`id` IN (4, 8, 15, 16, 23, 42))
+```
+
+If you'll specify value as `null` such as the following:
+
+```php
+$query->where(array(
+	'status' => null,
+));
+```
+
+SQL generated will be:
+
+```sql
+WHERE (`status` IS NULL)
+```
+
+Another way to use the method is the operand format which is `array(operator, operand1, operand2, ...)`.
+
+Operator can be one of the following:
+
+- `and`: the operands should be concatenated together using `AND`. For example,
+  `array('and', 'id=1', 'id=2')` will generate `id=1 AND id=2`. If an operand is an array,
+  it will be converted into a string using the rules described here. For example,
+  `array('and', 'type=1', array('or', 'id=1', 'id=2'))` will generate `type=1 AND (id=1 OR id=2)`.
+  The method will NOT do any quoting or escaping.
+- `or`: similar to the `and` operator except that the operands are concatenated using `OR`.
+- `between`: operand 1 should be the column name, and operand 2 and 3 should be the
+   starting and ending values of the range that the column is in.
+   For example, `array('between', 'id', 1, 10)` will generate `id BETWEEN 1 AND 10`.
+- `not between`: similar to `between` except the `BETWEEN` is replaced with `NOT BETWEEN`
+  in the generated condition.
+- `in`: operand 1 should be a column or DB expression, and operand 2 be an array representing
+  the range of the values that the column or DB expression should be in. For example,
+  `array('in', 'id', array(1, 2, 3))` will generate `id IN (1, 2, 3)`.
+  The method will properly quote the column name and escape values in the range.
+- `not in`: similar to the `in` operator except that `IN` is replaced with `NOT IN` in the generated condition.
+- `like`: operand 1 should be a column or DB expression, and operand 2 be a string or an array representing
+  the values that the column or DB expression should be like.
+  For example, `array('like', 'name', '%tester%')` will generate `name LIKE '%tester%'`.
+  When the value range is given as an array, multiple `LIKE` predicates will be generated and concatenated
+  using `AND`. For example, `array('like', 'name', array('%test%', '%sample%'))` will generate
+  `name LIKE '%test%' AND name LIKE '%sample%'`.
+  The method will properly quote the column name and escape values in the range.
+- `or like`: similar to the `like` operator except that `OR` is used to concatenate the `LIKE`
+  predicates when operand 2 is an array.
+- `not like`: similar to the `like` operator except that `LIKE` is replaced with `NOT LIKE`
+  in the generated condition.
+- `or not like`: similar to the `not like` operator except that `OR` is used to concatenate
+  the `NOT LIKE` predicates.
+
+If you are building parts of condition dynamically it's very convenient to use `andWhere` and `orWhere`:
+
+```php
+$status = 10;
+$search = 'yii';
+
+$query->where(array('status' => $status));
+if (!empty($search)) {
+	$query->addWhere('like', 'title', $search);
+}
+```
+
+In case `$search` isn't empty the following SQL will be generated:
+
+```sql
+WHERE (`status` = 10) AND (`title` LIKE '%yii%')
+```
+
+Order
+-----
+
+For odering results `orderBy` and `addOrderBy` could be used:
+
+```php
+$query->orderBy(array(
+	'id' => Query::SORT_ASC,
+	'name' => Query::SORT_DESC,
+));
+```
+
+Here we are ordering by `id` ascending and then by `name` descending.
+
+Group and Having
+----------------
+
+In order to add `GROUP BY` to generated SQL you can use the following:
+
+```php
+$query->groupBy('id, status');
+```
+
+If you want to add another field after using `groupBy`:
+
+```php
+$query->addGroupBy(array('created_at', 'updated_at'));
+```
+
+To add a `HAVING` condition the corresponding `having` method and its `andHaving` and `orHaving` can be used. Parameters
+for these are similar to the ones for `where` methods group:
+
+```php
+$query->having(array('status' => $status));
+```
+
+Limit and offset
+----------------
+
+To limit result to 10 rows `limit` can be used:
+
+```php
+$query->limit(10);
+```
+
+To skip 100 fist rows use:
+
+```php
+$query->offset(100);
+```
+
+Union
+-----
+
+`UNION` in SQL adds results of one query to results of another query. Columns returned by both queries should match.
+In Yii in order to build it you can first form two query objects and then use `union` method:
+
+```php
+$query = new Query;
+$query->select("id, 'post' as type, name")->from('tbl_post')->limit(10);
+
+$anotherQuery = new Query;
+$query->select('id, 'user' as type, name')->from('tbl_user')->limit(10);
+
+$query->union($anotherQuery);
+```
+