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This document describes how to generate and execute SQL queries using a query builder (mostly the builder was modelled off Laravel Query Builder, which already provides quite a thorough documentation - however some methods might be a bit different). Any significant difference will be outlined in this document as a separate paragraph.

...

Other functions

value()

Returns the a single value from a record. This method will return the value of the column directly.

$email = builder::table('users')
    ->where('name', 'John Doe')
    ->value('email');

$email = $DB->get_field('users', 'email', ['name' => 'John Doe']);

...

To select items from your database you should use select or add_select method, the first one overrides your SQL select statement, the latter one appends. Field names are passed through a standard regex check to help you against SQL injections.

Will give you the following result:

...

id

...

name

...

1

...

John Doe

Selecting aggregates

Sometimes you need to do more complex selects than just a field name, for example using aggregate functions, builder allows for it, treating it as valid column names. Most commonly aggregate functions are supported: MIN, MAX, AVG, SUM, COUNT.

Will give you the following result

...

Selecting subquery

It's possible to use subqueries in select statements as well

The above query should give you the following results:

...

If this is still not sufficient, then you might resort to the raw versions of the select methods:

Selecting raw statement

When you use select statement the field that you are attempting to select is validated against a regular expression "a-zA-Z-_|*" (it actually is a bit more complex to allow for aliases, aggregate functions and prefixes - more on that later). Sometimes though you might need to use more advanced SQL in select, to achieve it you might use raw methods, raw methods embed provided strings directly into SQL statement. Browse Raw methods to see the list of all available raw methods.

...

Joins

Inner join

Query builder might join other tables for you. To perform an inner join (or just join for simplification) you may use the join method, the first argument is the name of the table to join, the remaining arguments define the column in the main table, the condition and the column in the table being joined.

builder::table('users')
	->select(['id', 'name']) // Select or add_select accept a column to select as well as array of columns
	->first();

builder::table('users')
	->select('id')
	->add_select('name as name') // Adding as alias is supported as well and it will pass field validation check
	->first();

builder::table('users')
	->select('email')
	->select('id') // This will override any previous select or add_select statements and replace it with "id"
	->add_select('name') // This will append to "id" resulting in "id, name"
	->first();

Will give you the following result:

builder::table('users')
	->select('my field') // This will blow up and exception will be thrown here
	->first();

Selecting aggregates

Sometimes you need to do more complex selects than just a field name, for example using aggregate functions, builder allows for it, treating it as valid column names. Most commonly aggregate functions are supported: MIN, MAX, AVG, SUM, COUNT.

builder::table('orders')

    ->join('users', 'user_id	->select(['min(quantity) as min_quantity', 'id'max(quantity) // You can omit '=' condition in joins for convenience this will be equivalent to the code above 
    ->select('*', 'users.name as user_name') 
    as max_quantity'])
	->add_select('avg(quantity) as avg_quantity')
	->add_select('sum(quantity) as total_quantity')
	->add_select('count(id) as orders')
	->first();

...

Will give you the following

...

result:

Left join

To perform a left join use the following construct:

Right join

Full join

Cross join

Cross join is slightly different from all the previous joins as it does not take any arguments, only the table name.

Joining multiple tables

You may join multiple tables using the builder, simply call join several times on the builder object.

Will give you the following result:

Selecting subquery

It's possible to use subqueries in select statements as well:

builder::table('users')
	->select(['id', 'name', new subquery(function(builder $sub) {
		$sub->from('orders')
			->select('max(quantity)')
			->where('user_id', 'users.id');
	})->as('max_order_quantity'))
	->limit(2)
	->get();

The above query should give you the following results:

Complex condition joins

Sometimes you want to join tables on multiple conditions, this also possible via the builder, you would need to use the following syntax:

Alternative syntax

To define a custom alias for a joined table, you may use an alternative syntax for table field:

Sub query join

Sub query joins are possible, you will need to pass a query builder instance or subquery class instance instead of a table name to the join method. An alias must be specified for sub query joins.

Where clauses

Simple where clauses

You can use the where method to add where conditions to your query. Where accepts three arguments:

1. Name of column
2. The operator [=, in, <, > , <> or !=, <=, >=, like, ilike, ...]
3. The value to evaluate against the column

...

If this is still not sufficient, then you might resort to the raw versions of the select methods:

Selecting raw statement

When you use select statement the field that you are attempting to select is validated against a regular expression "a-zA-Z-_|*" (it actually is a bit more complex to allow for aliases, aggregate functions and prefixes - more on that later). Sometimes though you might need to use more advanced SQL in select, to achieve it you might use raw methods, raw methods embed provided strings directly into SQL statement. Browse Raw methods to see the list of all available raw methods.

builder::table('users')
    ->where	->select_raw('status'id, '=', 1)
    ->fetchname, :character as character', ["character" => "Good"])
	->first();

//When builder::table('users')
    ->where('votes', '<=' 50)
    ->where('status', '=', 1')
    ->fetch();

You can only supply two arguments, the column and the value. In this case depending on the value type, the operator defaults to = or in:

working with builder only named params are allowed, however if you need to use other types, you might use (raw)sql class.
use core\dml\sql;

builder::table('users')

	->select(new sql('id, name, ? as character, ["Good"])) // 

When 

you 

want 

to pass 

list($sql_in, $params) = $DB->get_in_or_equal([3, 4, 5, 6], SQL_PARAMS_NAMED);
$params['status'] = 1;
$users = $DB→get_records_select('users', "status = :status AND id $sql_in", $params);

OR statements

You can chain where clauses as well as add or_ clauses to the query. The or_where function accepts the same arguments as the where function.

// WHERE name = 'John Doe' OR name = 'Jane Doe'
$users =(raw)sql
	->first();

// Raw functions work the same way as regular select and add_select, 
// meaning that calling select_raw will override your select statement.
// Calling add_select_raw will append to your select statement, 
// it will add a comma delimiter, you don't need to manage it manually
// You may also combine raw and non-raw statements
builder::table('users')
    ->where	->select('nameid', 'John Doe)
	->add_select('name')
    ->or_where('name	->add_select_raw(':character as character', ['Jane Doe')
    ->fetch();

Nested where clauses / parameter grouping

...

character' => 'Good'])
	->first();

Joins

Inner join

Query builder might join other tables for you. To perform an inner join (or just join for simplification) you may use the join method, the first argument is the name of the table to join, the remaining arguments define the column in the main table, the condition and the column in the table being joined.

builder::table('usersorders')
    ->where>join('statususers', 1)
    ->where(function (builder $builder) {
  'user_id', '=', 'id') // Don't be alarmed that there is naming collision, the columns will be auto-prefixed automatically 
    $builder->where>select('name*', 'John Doeusers.name as user_name') // By default nothing from a joined table will be selected though, you need to  ->or_where('name', 'Jane Doe')append that manually 
    })->fetch>first();

Additional where clauses

where_field / or_where_field

This function allows to compare two columns. Both fields are passed through a standard regex field name check here, that should prevent you from basic SQL injections.

// WHERE last_login = created
$does =  

// Same result 
builder::table('usersorders') 
    ->where_field('last_login>join('users', 'user_id', 'createdid') // You can omit  ->fetch();

// WHERE last_login > created
$does = builder::table('users')
    ->where_field('last_login', '>', 'created')'=' condition in joins for convenience this will be equivalent to the code above 
    ->select('*', 'users.name as user_name') 
    ->fetch>first();

where_null / or_where_null / where_not_null / or_where_not_null

...

The above code will give you the following data selected:

Left join

To perform a left join use the following construct:

builder::table('usersorders')
    ->where_null('last_login')
    ->fetch();

// WHERE last_login IS NOT NULL
$does = 	->left_join('users', 'user_id', '=', 'id') 
	->select('*', 'users.name as user_name')
	->first();

Right join

builder::table('usersorders')
    ->where_not_null('last_login')
    ->fetch();

where_in / or_where_in / where_not_in / or_where_not_in

This is a shortcut for ->where('column', 'in', $value);

where_like / or_where_like / where_like_starts_with / or_where_like_starts_with / where_like_ends_with / or_where_like_ends_with

The builder provides some shortcuts for LIKE statements.

// WHERE name LIKE '%John%'
$users = builder::table('users')  
    ->where_like('name', 'John')    // ->where('name', 'like', 'John')
    ->fetch();

// WHERE name LIKE 'John%'
$users = builder::table('users')  
    ->where_like_starts_with('name', 'John')    // ->where('name', 'like_starts_with', 'John')
    ->fetch();

// WHERE name LIKE '%John'
$users = builder::table('users')  
    ->where_like_ends_with('name', 'Doe')    // ->where('name', 'like_ends_with', 'Doe')
    ->fetch();

$like_sql = $DB->sql_like('name', ':name');
$params = ['name' => '%'.$DB->sql_like_escape('John').'%'];
$users = $DB->get_records_select('users', $like_sql, $params);

By default the like comparisons are case-sensitive. If you need case-insensitive LIKE statements use: ilike, ilike_starts_with, ilike_ends_with

If you need NOT LIKE statements use: !like, !like_starts_with, !like_ends_with, !ilike, !ilike_starts_with, !ilike_ends_with

where_like_raw / or_where_like_raw

If none of the other like functions cover you need you can use the raw methods. The value won't be surrounded by any percentage signs, this needs to be handled by yourself.

$does = builder::table('users')
    ->where_like_raw('name', 'John%Doe')
    ->fetch();

where_exists / or_where_exists / where_not_exists / or_where_not_exists

The where_exists functions allows for creating a WHERE EXISTS (subquery) condition. It accepts a builder or a Closure argument, which will receive a new builder instance. This allows you to define the query that should be used inside the exists statement.

// SELECT * 
// FROM orders
// WHERE EXISTS (SELECT id FROM users WHERE name LIKE '%Doe' AND id = orders.user_id)
$second_builder = builder::table('users')
    ->select('id')
    ->where('name', 'like_ends_with', 'Doe')
    ->where_field('users.id', 'orders.user_id');

$orders	->right_join('users', 'user_id', '=', 'id')
	->select('*', 'users.name as user_name')
	->first();

Full join

builder::table('orders')
	->full_join('users', 'user_id', '=', 'id')
	->select('*', 'users.name as user_name')
	->first();

Cross join

Cross join is slightly different from all the previous joins as it does not take any arguments, only the table name.

builder::table('orders')
	->cross_join('users')
	->first();

Joining multiple tables

You may join multiple tables using the builder, simply call join several times on the builder object.

builder::table('orders')
	->join(['users', 'users'], 'user_id', 'id')
	->join('goods', 'goods_item', 'id')
	->select(['orders.id as order_id', 'users.name as user_name', 'goods.name as item_name', 'orders.quantity as quantity'])
	->first();

Will give you the following result:

Complex condition joins

Sometimes you want to join tables on multiple conditions, this also possible via the builder, you would need to use the following syntax:

builder::table('orders')
	->join('users', function(builder $joining, builder $builder) {
		$joining->where_field('orders.id', 'users.id') // You can add as many where conditions as you want here
			->where('users.name', '!=', 'Justin Bieber'); // Nah, no orders here
	})
	->first();

Alternative syntax

To define a custom alias for a joined table, you may use an alternative syntax for table field:

use core\orm\query\table;

// Using table class
builder::table('orders')
	->join((new table('users'))->as('u'), 'user_id', 'id')
	->select('*', 'u.name as user_name')
	->first();

// Or using array syntax
builder::table('orders')
	->join(['users', 'u'], 'user_id', 'id')
	->select('*', 'u.name as user_name')
	->first();

// They both will achieve the same result
// If you examine the code, the second one internally will 
// be translated to the first one, saving you from a cumbersome syntax constructs

Sub query join

Sub query joins are possible, you will need to pass a query builder instance or subquery class instance instead of a table name to the join method. An alias must be specified for sub query joins.

use core\orm\query\table;
use core\orm\query\subquery;

$sub_query = builder::table('ordersusers')
				->where_exists($second_builder)
    ->fetch(('status', 1);

// AlternativeA $ordersbasic =way
builder::table('orders')
    ->where_exists(function(builder $builder) {
        $builder	->join((new table($sub_query))->as('u'), 'user_id', 'id')
	->select('id*'), 'u.name as user_name')
	->first();

// Using short syntax
   ->where('name'builder::table('orders')
	->join([$sub_query, 'u'], 'likeuser_ends_withid', 'Doeid')
            ->where_field('users.id	->select('*', 'ordersu.name as user_idname');
    })->fetch();

Raw where clauses

If you need to pass a raw condition to your query you can either pass an instance of SQL to your clause:

$sql = new sql("name = :name", ['name' => 'John']); 

$users =
	->first();

// Using subquery class
builder::table('usersorders')
    ->where($sql)
    ->fetch();

Alternative, use the provided raw methods, passing the SQL part as first and the params as second argument:

• where_raw

• or_where_raw

$users = builder::table('users')
    ->where_raw("name = :name", ['name' => 'John'])
    ->fetch();

Complex example

	->join((new subquery($sub_query))->as('u'), 'user_id', 'id')
	->select('*', 'u.name as user_name')
	->first();

Where clauses

Simple where clauses

You can use the where method to add where conditions to your query. Where accepts three arguments:

1. Name of column
2. The operator [=, in, <, > , <> or !=, <=, >=, like, ilike, ...]
3. The value to evaluate against the column

Where provides a fluent interface and can be chained. By default the value will always end up as a named parameter, means it's protected against SQL injection.

builder::table('users')
    ->where('status', '=', 1)
    ->fetch(); 

builder::table('users'

)

->where('

votes', '<='

50)
    -

>where('

status', '='

, 

1')
    -

>fetch();

You can only supply two arguments, the column and the value. In this case depending on the value type, the operator defaults to = or in:

$users = builder::table('users')  
    ->where('status', 1) // defaults to =      
     ->or_where_null>where('last_login');
    })
    ->where_like_ends_with('email', 'gmail.com'id', [3, 4, 5, 6]) // defaults to in()
    ->fetch();

Group by multiple columns

If you need to group results by multiple columns, builder allows you to do that doing multiple calls to group_by method.

Builders also allows you to reset any order condition added, by calling reset_group_by() method or passing null to the group_by() method.

Group by raw value

If you need some more complex grouping, you may resort to a raw method group_by_raw to embed a raw string into the query. It works in a similar manner to order_by_raw and add_select_raw:

Offsetting or limiting the results

limit()

Will add limit to the results:

$select = "(name = :name1 OR name = :name2) AND (status = :status OR last_login IS NULL) AND $like_sql";
$params = [
    'name1' => 'John Doe',
    'name2' => 'Jane Doe',
    'status' => 1
];

$like_sql = $DB->sql_like('email', ':email');
$params['email'] = '%'.$DB->sql_like_escape('gmail.com');

$users = $DB→get_records_select('users', "status = :status AND id $sql_in", $params);

Order

Order by a column

It's quite easy to add order statements to the query using query builder. To simply order by a column name you should use order_by method.

It takes the column name to sort by as first argument, the second argument is optional defining order direction, ascending (asc) or descending (desc), defaulting to ascending.

This will give you the following result

...

Order by multiple columns

If you need to order by multiple columns subsequent calls to order_by will achieve that. Each call to order_by appends to order condition SQL.

This would give you the following results:

...

Builders also allows you to reset any order condition added, by calling reset_order_by() method or passing null to the order_by() method.

The above code would give you the following result:

...

Order by raw statement

Similar to column names passed to select and add_select methods, column names are validated to protect you against accidental SQL injection. However if you require order by raw statement it is achievable calling order_by_raw method

You may also use (raw) sql with order_by:

Grouping

Group by a column

If you need to group results by a column, builder allows you to do that and there is a group_by method to do that.

Should give you the following result:

...

list($sql_in, $params) = $DB->get_in_or_equal([3, 4, 5, 6], SQL_PARAMS_NAMED);
$params['status'] = 1;
$users = $DB→get_records_select('users', "status = :status AND id $sql_in", $params);

OR statements

You can chain where clauses as well as add or_ clauses to the query. The or_where function accepts the same arguments as the where function.

// WHERE name = 'John Doe' OR name = 'Jane Doe'
$users = builder::table('users')
    ->where('name', 'John Doe')
    ->or_where('name', 'Jane Doe')
    ->fetch();

Nested where clauses / parameter grouping

If you need to group where clauses you can use the nested where functionality. Just pass a Closure argument, which will receive the nested builder as an argument.

// WHERE status = 1 AND (name = 'John Doe' OR name = 'Jane Doe')
$does = builder::table('users')
    ->where('status', 1)
    ->where(function (builder $builder) {
        $builder->where('name', 'John Doe')
            ->or_where('name', 'Jane Doe')
    })->fetch();

Additional where clauses

where_field / or_where_field

This function allows to compare two columns. Both fields are passed through a standard regex field name check here, that should prevent you from basic SQL injections.

// WHERE last_login = created
$does = builder::table('users')
    ->where_field('last_login', 'created')
    ->fetch();

// WHERE last_login > created
$does = builder::table('users')
    ->where_field('last_login', '>', 'created')
    ->fetch();

where_null / or_where_null / where_not_null / or_where_not_null

This is a shortcut for ->where('column', null);

// WHERE last_login IS NULL
$does = builder::table('users')
	->limit(1) 	->get();  // Usually used together with limit
$users = builder::table('users')
	->first(); ->where_null('last_login')
    ->fetch();

// CallingWHERE firstlast_login willIS addNOT limit 1 to the query

offset()

Will add offset to the query:

$usersNULL
$does = builder::table('users')
	->offset(1)
	->get();

// Usually used together with limit
$users = builder::table('users')
	->offset(1)
	->limit(1)
	->get();

Unions

The query builder also provides easy means to unite two queries together. Here is how it works.

This what the result of $users would be:

...

Field auto-prefixing

If you do not specify an alias on your builder then the builder automatically will use the table name (without the prefix) as the alias. You can specify your own alias by using the as() function or pass it as second argument to the builder::table() function.

All columns used in select, add_select, group_by, having, or_having, where, or_where, join, etc. will automatically be prefixed with the proper alias. You can also manually specify the alias in the column with the dot-syntax (i.e. 'users.name').

In more detail

It might seem that when using query builder and referring to fields the field prefix is not included. That's on the surface only to make it easier for developers. All the fields passed to the fielder without using raw functions which includes: select, add_select, group_by, having, or_having, where, or_where, join, etc. prefix fields with either a table name given (without moodle table prefix, e.g. mdl_). On the query builder you may specify an alias for the table the builder is for by calling as() or by passing the alias as second argument to the builder::table()function. This will result in all fields passed to the builder to be prefixed with the given alias when SQL is generated. If however the alias is not set, the fields still will be prefixed but with the table name instead, in the form of "{table}".

For joined tables, they will be automatically aliased with the table name without moodle prefix e.g. for mdl_user it will pre prefixed with user. This behaviour is designed to allow more natural flow when building query, for example you can add where('user.name', 'John) instead of where('{user}.name', 'John). It's smart enough not to prefix fields if they are already prefixed, or add prefix correctly if as or aggregate function is specified. How it works behind the scenes, if string is passed to the method that accepts a field, it wraps it in a field() class which in turn is responsible to add prefix if needed. Field class accepts a name and a link to a builder instance it should belong to.

All these functions support overloading and you may pass a field class directly, if you didn't link it to any other builder, it will be linked to the current automatically. Field class has some built in subclasses for convenience, including raw_field and subquery (technically field is a subclass of raw field). Subquery accepts a builder and allows you to specify an alias as. The application is to use it in select, where you need to select a subquery.

...

    ->where_not_null('last_login')
    ->fetch();

where_in / or_where_in / where_not_in / or_where_not_in

This is a shortcut for ->where('column', 'in', $value);

where_like / or_where_like / where_like_starts_with / or_where_like_starts_with / where_like_ends_with / or_where_like_ends_with

The builder provides some shortcuts for LIKE statements.

// WHERE name LIKE '%John%'
$users = builder::table('users')  
    ->where_like('name', 'John')    // ->where('name', 'like', 'John')
    ->fetch();

// WHERE name LIKE 'John%'
$users = builder::table('users')  
    ->where_like_starts_with('name', 'John')    // ->where('name', 'like_starts_with', 'John')
    ->fetch();

// WHERE name LIKE '%John'
$users = builder::table('users')  
    ->where_like_ends_with('name', 'Doe')    // ->where('name', 'like_ends_with', 'Doe')
    ->fetch();

$like_sql = $DB->sql_like('name', ':name');
$params = ['name' => '%'.$DB->sql_like_escape('John').'%'];
$users = $DB->get_records_select('users', $like_sql, $params);

By default the like comparisons are case-sensitive. If you need case-insensitive LIKE statements use: ilike, ilike_starts_with, ilike_ends_with

If you need NOT LIKE statements use: !like, !like_starts_with, !like_ends_with, !ilike, !ilike_starts_with, !ilike_ends_with

where_like_raw / or_where_like_raw

If none of the other like functions cover you need you can use the raw methods. The value won't be surrounded by any percentage signs, this needs to be handled by yourself.

$does = builder::table('users')
    ->where_like_raw('name', 'John%Doe')
    ->fetch();

where_exists / or_where_exists / where_not_exists / or_where_not_exists

The where_exists functions allows for creating a WHERE EXISTS (subquery) condition. It accepts a builder or a Closure argument, which will receive a new builder instance. This allows you to define the query that should be used inside the exists statement.

// SELECT * 
// FROM orders
// WHERE EXISTS (SELECT id FROM users WHERE name LIKE '%Doe' AND id = orders.user_id)
$second_builder = builder::table('users')
    ->select('id')
    ->where('name', 'like_ends_with', 'Doe')
    ->where_field('users.id', 'orders.user_id');

$orders = builder::table('orders')
	->where_exists($second_builder)
    ->fetch();

// Alternative
$orders = builder::table('orders')
    ->where_exists(function(builder $builder) {
        $builder->select('id')
            ->where('name', 'like_ends_with', 'Doe')
            ->where_field('users.id', 'orders.user_id');
    })->fetch();

Raw where clauses

If you need to pass a raw condition to your query you can either pass an instance of SQL to your clause:

$sql = new sql("name = :name", ['name' => 'John']); 

$users = builder::table('users')
    ->where($sql)
    ->fetch();

Alternative, use the provided raw methods, passing the SQL part as first and the params as second argument:

• where_raw

• or_where_raw

$users = builder::table('users')
    ->where_raw("name = :name", ['name' => 'John'])
    ->fetch();

Complex example

// WHERE (name = 'John Doe' OR name = 'Jane Doe') AND (status = 1 OR last_login IS NULL) AND email LIKE '%gmail.com'
$users = builder::table('users')
    ->where(function (builder $builder) {
        $builder->where('name', 'John Doe')
            ->or_where('name', 'Jane Doe');
    })
    ->where(function (builder $builder) {
        $builder->where('status', 1)
            ->or_where_null('last_login');
    })
    ->where_like_ends_with('email', 'gmail.com')
    ->fetch();

$select = "(name = :name1 OR name = :name2) AND (status = :status OR last_login IS NULL) AND $like_sql";
$params = [
    'name1' => 'John Doe',
    'name2' => 'Jane Doe',
    'status' => 1
];

$like_sql = $DB->sql_like('email', ':email');
$params['email'] = '%'.$DB->sql_like_escape('gmail.com');

$users = $DB→get_records_select('users', "status = :status AND id $sql_in", $params);

Order

Order by a column

It's quite easy to add order statements to the query using query builder. To simply order by a column name you should use order_by method.

It takes the column name to sort by as first argument, the second argument is optional defining order direction, ascending (asc) or descending (desc), defaulting to ascending.

builder::table('orders')
	->select(['id', 'name'])
	->order_by('name', 'asc')
	->limit(2)
	->get();

This will give you the following result

Order by multiple columns

If you need to order by multiple columns subsequent calls to order_by will achieve that. Each call to order_by appends to order condition SQL.

builder::table('orders')
	->select(['id', 'name', 'status'])
	->order_by('status', 'asc')
	->order_by('name', 'asc')
	->limit(2)
	->get();

This would give you the following results:

Builders also allows you to reset any order condition added, by calling reset_order_by() method or passing null to the order_by() method.

builder::table('orders')
	->select(['id', 'name'])
	->order_by('status', 'asc')
	->order_by('name', 'asc')
	->reset_order_by()
	->order_by('id', 'desc')
	->limit(2)
	->get();

The above code would give you the following result:

Order by raw statement

Similar to column names passed to select and add_select methods, column names are validated to protect you against accidental SQL injection. However if you require order by raw statement it is achievable calling order_by_raw method:

builder::table('orders')
	->select(['id', 'name'])
	->order_by_raw('id asc, name desc')
	->limit(2)
	->get();

You may also use (raw) sql with order_by:

use core\dml\sql;

builder::table('orders')
	->select(['id', 'name'])
	->order_by(new sql('name asc'))
	->limit(2)
	->get();

Grouping

Group by a column

If you need to group results by a column, builder allows you to do that and there is a group_by method to do that.

builder::table('orders')
	->join('users', 'id', 'user_id')
	->select(['users.name as user_name', 'max(quantity) as max_quantity'])
	->group_by('users.name')
	->order_by('max(quantity)')
	->limit(2)
	->get();

Should give you the following result:

Group by multiple columns

If you need to group results by multiple columns, builder allows you to do that doing multiple calls to group_by method.

builder::table('orders')
	->join('users', 'id', 'user_id')
	->select(['users.name as user_name', 'max(quantity) as max_quantity', 'orders.id'])
	->group_by('users.name')
	->group_by('id')
	->order_by('max(quantity)')
	->limit(2)
	->get();

Builders also allows you to reset any order condition added, by calling reset_group_by() method or passing null to the group_by() method.

Group by raw value

If you need some more complex grouping, you may resort to a raw method group_by_raw to embed a raw string into the query. It works in a similar manner to order_by_raw and add_select_raw:

builder::table('orders')
	->join('users', 'id', 'user_id')
	->select(['users.name as user_name', 'max(quantity) as max_quantity'])
	->group_by_raw('"users".name')
	->order_by('max(quantity)')
	->limit(2)
	->get();

Offsetting or limiting the results

limit()

Will add limit to the results:

$users = builder::table('users')
	->limit(1)
	->get();

// Usually used together with limit
$users = builder::table('users')
	->first(); // Calling first will add limit 1 to the query

offset()

Will add offset to the query:

$users = builder::table('users')
	->offset(1)
	->get();

// Usually used together with limit
$users = builder::table('users')
	->offset(1)
	->limit(1)
	->get();

Unions

The query builder also provides easy means to unite two queries together. Here is how it works.

$gmail_users = builder::table('users')
	->select(['id', 'name'])
	->where('email', 'like_ends_with', 'gmail.com');

$users = builder::table('users')
	->select_raw('id, name')
	->where('email', 'like_ends_with', 'gmail.com')
	->union($gmail_users)
	->get();

// You may also do union all, however that might result in debugging notice 
// due to the fact that $DB always requires the first column to be unique :shrug:
$all = builder::table('users')
	->select_raw('id, name')
	->union_all($gmail_users)
	->get();

This what the result of $users would be:

Field auto-prefixing

If you do not specify an alias on your builder then the builder automatically will use the table name (without the prefix) as the alias. You can specify your own alias by using the as() function or pass it as second argument to the builder::table() function.

All columns used in select, add_select, group_by, having, or_having, where, or_where, join, etc. will automatically be prefixed with the proper alias. You can also manually specify the alias in the column with the dot-syntax (i.e. 'users.name').

In more detail

It might seem that when using query builder and referring to fields the field prefix is not included. That's on the surface only to make it easier for developers. All the fields passed to the fielder without using raw functions which includes: select, add_select, group_by, having, or_having, where, or_where, join, etc. prefix fields with either a table name given (without moodle table prefix, e.g. mdl_). On the query builder you may specify an alias for the table the builder is for by calling as() or by passing the alias as second argument to the builder::table()function. This will result in all fields passed to the builder to be prefixed with the given alias when SQL is generated. If however the alias is not set, the fields still will be prefixed but with the table name instead, in the form of "{table}".

For joined tables, they will be automatically aliased with the table name without moodle prefix e.g. for mdl_user it will pre prefixed with user. This behaviour is designed to allow more natural flow when building query, for example you can add where('user.name', 'John) instead of where('{user}.name', 'John). It's smart enough not to prefix fields if they are already prefixed, or add prefix correctly if as or aggregate function is specified. How it works behind the scenes, if string is passed to the method that accepts a field, it wraps it in a field() class which in turn is responsible to add prefix if needed. Field class accepts a name and a link to a builder instance it should belong to.

All these functions support overloading and you may pass a field class directly, if you didn't link it to any other builder, it will be linked to the current automatically. Field class has some built in subclasses for convenience, including raw_field and subquery (technically field is a subclass of raw field). Subquery accepts a builder and allows you to specify an alias as. The application is to use it in select, where you need to select a subquery.

Let's get to some code examples to get better understanding of all this.

// Will generate the following sql before it goes to the DML layer:
// SELECT "users".id, "users".name FROM {users} users WHERE 1 = 1
builder::table('users')
	->select(['id', 'name'])
	->get();

// Will generate the following sql before it goes to the DML layer:
// SELECT "u".id, "u".name FROM {users} u WHERE 1 = 1
builder::table('users')
	->as('u')
	->select(['id', 'name'])
	->get();

// Will generate the following sql before it goes to the DML layer:
// SELECT "u".id, "u".name, "orders".quantity 
// FROM {users} u 
// JOIN {orders} orders ON ("u.id" = "orders".user_id) 
// WHERE 1 = 1 
// ORDER BY "u".name ASC
builder::table('users', 'u')
	->join('orders', 'id', 'user_id')
	->select(['id', 'name', 'orders.quantity'])
	->order_by('name')
	->get();

Raw methods

In addition to some query building methods query builder offers a raw version which has a suffix '_raw' and accepts two arguments: SQL and parameters. These methods embed provided sql in the appropriate part of the query.

List of available raw methods:

...