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Query Builder

Built on top of Database Access Objects, query builder allows you to construct a SQL statement in a programmatic and DBMS-agnostic way. Compared to writing raw SQL statements, using query builder will help you write more readable SQL-related code and generate more secure SQL statements.

Using query builder usually involves two steps:

  1. Build a [[yii\db\Query]] object to represent different parts (e.g. SELECT, FROM) of a SELECT SQL statement.
  2. Execute a query method (e.g. all()) of [[yii\db\Query]] to retrieve data from the database.

The following code shows a typical way of using query builder:

$rows = (new \yii\db\Query())
    ->select(['id', 'email'])
    ->from('user')
    ->where(['last_name' => 'Smith'])
    ->limit(10)
    ->all();

The above code generates and executes the following SQL statement, where the :last_name parameter is bound with the string 'Smith'.

SELECT `id`, `email` 
FROM `user`
WHERE `last_name` = :last_name
LIMIT 10

Info: You usually mainly work with [[yii\db\Query]] instead of [[yii\db\QueryBuilder]]. The latter is invoked by the former implicitly when you call one of the query methods. [[yii\db\QueryBuilder]] is the class responsible for generating DBMS-dependent SQL statements (e.g. quoting table/column names differently) from DBMS-independent [[yii\db\Query]] objects.

Building Queries

To build a [[yii\db\Query]] object, you call different query building methods to specify different parts of a SQL statement. The names of these methods resemble the SQL keywords used in the corresponding parts of the SQL statement. For example, to specify the FROM part of a SQL statement, you would call the from() method. All the query building methods return the query object itself, which allows you to chain multiple calls together.

In the following, we will describe the usage of each query building method.

[[yii\db\Query::select()|select()]]

The [[yii\db\Query::select()|select()]] method specifies the SELECT fragment of a SQL statement. You can specify columns to be selected in either an array or a string, like the following. The column names being selected will be automatically quoted when the SQL statement is being generated from a query object.

$query->select(['id', 'email']);

// equivalent to:

$query->select('id, email');

The column names being selected may include table prefixes and/or column aliases, like you do when writing raw SQL statements. For example,

$query->select(['user.id AS user_id', 'email']);

// equivalent to:

$query->select('user.id AS user_id, email');

If you are using the array format to specify columns, you can also use the array keys to specify the column aliases. For example, the above code can be rewritten as follows,

$query->select(['user_id' => 'user.id', 'email']);

If you do not call the [[yii\db\Query::select()|select()]] method when building a query, * will be selected, which means selecting all columns.

Besides column names, you can also select DB expressions. You must use the array format when selecting a DB expression that contains commas to avoid incorrect automatic name quoting. For example,

$query->select(["CONCAT(first_name, ' ', last_name) AS full_name", 'email']);

Starting from version 2.0.1, you may also select sub-queries. You should specify each sub-query in terms of a [[yii\db\Query]] object. For example,

$subQuery = (new Query())->select('COUNT(*)')->from('user');

// SELECT `id`, (SELECT COUNT(*) FROM `user`) AS `count` FROM `post`
$query = (new Query())->select(['id', 'count' => $subQuery])->from('post');

To select distinct rows, you may call [[yii\db\Query::distinct()|distinct()]], like the following:

// SELECT DISTINCT `user_id` ...
$query->select('user_id')->distinct();

You can call [[yii\db\Query::addSelect()|addSelect()]] to select additional columns. For example,

$query->select(['id', 'username'])
    ->addSelect(['email']);

[[yii\db\Query::from()|from()]]

The [[yii\db\Query::from()|from()]] method specifies the FROM fragment of a SQL statement. For example,

// SELECT * FROM `user`
$query->from('user');

You can specify the table(s) being selected from in either a string or an array. The table names may contain schema prefixes and/or table aliases, like you do when writing raw SQL statements. For example,

$query->from(['public.user u', 'public.post p']);

// equivalent to:

$query->from('public.user u, public.post p');

If you are using the array format, you can also use the array keys to specify the table aliases, like the following:

$query->from(['u' => 'public.user', 'p' => 'public.post']);

Besides table names, you can also select from sub-queries by specifying them in terms of [[yii\db\Query]] objects. For example,

$subQuery = (new Query())->select('id')->from('user')->where('status=1');

// SELECT * FROM (SELECT `id` FROM `user` WHERE status=1) u 
$query->from(['u' => $subQuery]);

[[yii\db\Query::where()|where()]]

The [[yii\db\Query::where()|where()]] method specifies the WHERE fragment of a SQL statement. You can use one of the three formats to specify a WHERE condition:

  • string format, e.g., 'status=1'
  • hash format, e.g. ['status' => 1, 'type' => 2]
  • operator format, e.g. ['like', 'name', 'test']

String Format

String format is best used to specify very simple conditions. It works as if you are writing a raw SQL. For example,

$query->where('status=1');

// or use parameter binding to bind dynamic parameter values
$query->where('status=:status', [':status' => $status]);

Do NOT embed variables directly in the condition like the following, especially if the variable values come from end user inputs, because this will make your application subject to SQL injection attacks.

// Dangerous! Do NOT do this unless you are very certain $status must be an integer.
$query->where("status=$status");

When using parameter binding, you may call [[yii\db\Query::params()|params()]] or [[yii\db\Query::addParams()|addParams()]] to specify parameters separately.

$query->where('status=:status')
    ->addParams([':status' => $status]);

Hash Format

Hash format is best used to specify multiple AND-concatenated sub-conditions each being a simple equality assertion. It is written as an array whose keys are column names and values the corresponding values that the columns should be. For example,

// ...WHERE (`status` = 10) AND (`type` IS NULL) AND (`id` IN (4, 8, 15))
$query->where([
    'status' => 10,
    'type' => null,
    'id' => [4, 8, 15],
]);

As you can see, the query builder is intelligent enough to properly handle values that are nulls or arrays.

You can also use sub-queries with hash format like the following:

$userQuery = (new Query())->select('id')->from('user');

// ...WHERE `id` IN (SELECT `id` FROM `user`)
$query->where(['id' => $userQuery]);

Operator Format

Operator format allows you to specify arbitrary conditions in a programmatic way. It takes the following format:

[operator, operand1, operand2, ...]

where the operands can each be specified in string format, hash format or operator format recursively, while the operator can be one of the following:

  • and: the operands should be concatenated together using AND. For example, ['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, ['and', 'type=1', ['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, ['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. Operand 2 can be either an array or a Query object. It will generate an IN condition. If Operand 2 is an array, it will represent the range of the values that the column or DB expression should be; If Operand 2 is a Query object, a sub-query will be generated and used as the range of the column or DB expression. For example, ['in', 'id', [1, 2, 3]] will generate id IN (1, 2, 3). The method will properly quote the column name and escape values in the range. The in operator also supports composite columns. In this case, operand 1 should be an array of the columns, while operand 2 should be an array of arrays or a Query object representing the range of the columns.

  • 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, ['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, ['like', 'name', ['test', 'sample']] will generate name LIKE '%test%' AND name LIKE '%sample%'. You may also provide an optional third operand to specify how to escape special characters in the values. The operand should be an array of mappings from the special characters to their escaped counterparts. If this operand is not provided, a default escape mapping will be used. You may use false or an empty array to indicate the values are already escaped and no escape should be applied. Note that when using an escape mapping (or the third operand is not provided), the values will be automatically enclosed within a pair of percentage characters.

    Note: When using PostgreSQL you may also use ilike instead of like for case-insensitive matching.

  • 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.

  • exists: requires one operand which must be an instance of [[yii\db\Query]] representing the sub-query. It will build a EXISTS (sub-query) expression.

  • not exists: similar to the exists operator and builds a NOT EXISTS (sub-query) expression.

  • >, <=, or any other valid DB operator that takes two operands: the first operand must be a column name while the second operand a value. For example, ['>', 'age', 10] will generate age>10.

Appending Conditions

You can use [[yii\db\Query::andWhere()|andWhere()]] or [[yii\db\Query::orWhere()|orWhere()]] to append additional conditions to an existing one. You can call them multiple times to append multiple conditions separately. For example,

$status = 10;
$search = 'yii';

$query->where(['status' => $status]);

if (!empty($search)) {
    $query->andWhere(['like', 'title', $search]);
}

If $search is not empty, the following SQL statement will be generated:

... WHERE (`status` = 10) AND (`title` LIKE '%yii%')

Filter Conditions

When building WHERE conditions based on input from end users, you usually want to ignore those empty input values. For example, in a search form that allows you to search by username and email, you would like to ignore the username/email condition if the user does not enter anything in the username/email input field. You can achieve this goal by using the [[yii\db\Query::filterWhere()|filterWhere()]] method:

// $username and $email are from user inputs
$query->filterWhere([
    'username' => $username,
    'email' => $email,
]);

The only difference between [[yii\db\Query::filterWhere()|filterWhere()]] and [[yii\db\Query::where()|where()]] is that the former will ignore empty values provided in the condition in hash format. So if $email is empty while $username is not, the above code will result in the SQL ...WHERE username=:username.

Info: A value is considered empty if it is null, an empty array, an empty string or a string consisting of whitespaces only.

Like [[yii\db\Query::andWhere()|andWhere()]] and [[yii\db\Query::orWhere()|orWhere()]], you can use [[yii\db\Query::andFilterWhere()|andFilterWhere()]] and [[yii\db\Query::orFilterWhere()|orFilterWhere()]] to append additional filter conditions to the existing one.

[[yii\db\Query::orderBy()|orderBy()]]

The [[yii\db\Query::orderBy()|orderBy()]] method specifies the ORDER BY fragment of a SQL statement. For example,

// ... ORDER BY `id` ASC, `name` DESC
$query->orderBy([
    'id' => SORT_ASC,
    'name' => SORT_DESC,
]);

In the above code, the array keys are column names while the array values are the corresponding order-by directions. The PHP constant SORT_ASC specifies ascending sort and SORT_DESC descending sort.

If ORDER BY only involves simple column names, you can specify it using a string, just like you do when writing raw SQL statements. For example,

$query->orderBy('id ASC, name DESC');

Note: You should use the array format if ORDER BY involves some DB expression.

You can call [[yii\db\Query::addOrderBy()|addOrderBy()]] to add additional columns to the ORDER BY fragment. For example,

$query->orderBy('id ASC')
    ->addOrderBy('name DESC');

[[yii\db\Query::groupBy()|groupBy()]]

The [[yii\db\Query::groupBy()|groupBy()]] method specifies the GROUP BY fragment of a SQL statement. For example,

// ... GROUP BY `id`, `status`
$query->groupBy(['id', 'status']);

If GROUP BY only involves simple column names, you can specify it using a string, just like you do when writing raw SQL statements. For example,

$query->groupBy('id, status');

Note: You should use the array format if GROUP BY involves some DB expression.

You can call [[yii\db\Query::addGroupBy()|addGroupBy()]] to add additional columns to the GROUP BY fragment. For example,

$query->groupBy(['id', 'status'])
    ->addGroupBy('age');

[[yii\db\Query::having()|having()]]

The [[yii\db\Query::having()|having()]] method specifies the HAVING fragment of a SQL statement. It takes a condition which can be specified in the same way as that for where(). For example,

// ... HAVING `status` = 1
$query->having(['status' => 1]);

Please refer to the documentation for where() for more details about how to specify a condition.

You can call [[yii\db\Query::andHaving()|andHaving()]] or [[yii\db\Query::orHaving()|orHaving()]] to append additional conditions to the HAVING fragment. For example,

// ... HAVING (`status` = 1) AND (`age` > 30)
$query->having(['status' => 1])
    ->andHaving(['>', 'age', 30]);

[[yii\db\Query::limit()|limit()]] and [[yii\db\Query::offset()|offset()]]

The [[yii\db\Query::limit()|limit()]] and [[yii\db\Query::offset()|offset()]] methods specify the LIMIT and OFFSET fragments of a SQL statement. For example,

// ... LIMIT 10 OFFSET 20
$query->limit(10)->offset(20);

If you specify an invalid limit or offset (e.g. a negative value), it will be ignored.

Info: For DBMS that do not support LIMIT and OFFSET (e.g. MSSQL), query builder will generate a SQL statement that emulates the LIMIT/OFFSET behavior.

[[yii\db\Query::join()|join()]]

The [[yii\db\Query::join()|join()]] method specifies the JOIN fragment of a SQL statement. For example,

// ... LEFT JOIN `post` ON `post`.`user_id` = `user`.`id`
$query->join('LEFT JOIN', 'post', 'post.user_id = user.id');

The [[yii\db\Query::join()|join()]] method takes four parameters:

  • $type: join type, e.g., 'INNER JOIN', 'LEFT JOIN'.
  • $table: the name of the table to be joined.
  • $on: optional, the join condition, i.e., the ON fragment. Please refer to where() for details about specifying a condition.
  • $params: optional, the parameters to be bound to the join condition.

You can use the following shortcut methods to specify INNER JOIN, LEFT JOIN and RIGHT JOIN, respectively.

  • [[yii\db\Query::innerJoin()|innerJoin()]]
  • [[yii\db\Query::leftJoin()|leftJoin()]]
  • [[yii\db\Query::rightJoin()|rightJoin()]]

For example,

$query->leftJoin('post', 'post.user_id = user.id');

To join with multiple tables, call the above join methods multiple times, once for each table.

Besides joining with tables, you can also join with sub-queries. To do so, specify the sub-queries to be joined as [[yii\db\Query]] objects. For example,

$subQuery = (new \yii\db\Query())->from('post');
$query->leftJoin(['u' => $subQuery], 'u.id = author_id');

In this case, you should put the sub-query in an array and use the array key to specify the alias.

[[yii\db\Query::union()|union()]]

The [[yii\db\Query::union()|union()]] method specifies the UNION fragment of a SQL statement. For example,

$query1 = (new \yii\db\Query())
    ->select("id, category_id AS type, name")
    ->from('post')
    ->limit(10);

$query2 = (new \yii\db\Query())
    ->select('id, type, name')
    ->from('user')
    ->limit(10);

$query1->union($query2);

You can call [[yii\db\Query::union()|union()]] multiple times to append more UNION fragments.

Query Methods

[[yii\db\Query]] provides a whole set of methods for different query purposes:

  • [[yii\db\Query::all()|all()]]: returns an array of rows with each row being an associative array of name-value pairs.
  • [[yii\db\Query::one()|one()]]: returns the first row of the result.
  • [[yii\db\Query::column()|column()]]: returns the first column of the result.
  • [[yii\db\Query::scalar()|scalar()]]: returns a scalar value located at the first row and first column of the result.
  • [[yii\db\Query::exists()|exists()]]: returns a value indicating whether the query contains any result.
  • [[yii\db\Query::count()|count()]]: returns the result of a COUNT query.
  • Other aggregation query methods, including [[yii\db\Query::sum()|sum($q)]], [[yii\db\Query::average()|average($q)]], [[yii\db\Query::max()|max($q)]], [[yii\db\Query::min()|min($q)]]. The $q parameter is mandatory for these methods and can be either a column name or a DB expression.

For example,

// SELECT `id`, `email` FROM `user`
$rows = (new \yii\db\Query())
    ->select(['id', 'email'])
    ->from('user')
    ->all();
    
// SELECT * FROM `user` WHERE `username` LIKE `%test%`
$row = (new \yii\db\Query())
    ->from('user')
    ->where(['like', 'username', 'test'])
    ->one();

Note: The [[yii\db\Query::one()|one()]] method only returns the first row of the query result. It does NOT add LIMIT 1 to the generated SQL statement. This is fine and preferred if you know the query will return only one or a few rows of data (e.g. if you are querying with some primary keys). However, if the query may potentially result in many rows of data, you should call limit(1) explicitly to improve the performance, e.g., (new \yii\db\Query())->from('user')->limit(1)->one().

All these query methods take an optional $db parameter representing the [[yii\db\Connection|DB connection]] that should be used to perform a DB query. If you omit this parameter, the db application component will be used as the DB connection. Below is another example using the count() query method:

// executes SQL: SELECT COUNT(*) FROM `user` WHERE `last_name`=:last_name
$count = (new \yii\db\Query())
    ->from('user')
    ->where(['last_name' => 'Smith'])
    ->count();

When you call a query method of [[yii\db\Query]], it actually does the following work internally:

  • Call [[yii\db\QueryBuilder]] to generate a SQL statement based on the current construct of [[yii\db\Query]];
  • Create a [[yii\db\Command]] object with the generated SQL statement;
  • Call a query method (e.g. queryAll()) of [[yii\db\Command]] to execute the SQL statement and retrieve the data.

Sometimes, you may want to examine or use the SQL statement built from a [[yii\db\Query]] object. You can achieve this goal with the following code:

$command = (new \yii\db\Query())
    ->select(['id', 'email'])
    ->from('user')
    ->where(['last_name' => 'Smith'])
    ->limit(10)
    ->createCommand();
    
// show the SQL statement
echo $command->sql;
// show the parameters to be bound
print_r($command->params);

// returns all rows of the query result
$rows = $command->queryAll();

Indexing Query Results

When you call [[yii\db\Query::all()|all()]], it will return an array of rows which are indexed by consecutive integers. Sometimes you may want to index them differently, such as indexing by a particular column or expression values. You can achieve this goal by calling [[yii\db\Query::indexBy()|indexBy()]] before [[yii\db\Query::all()|all()]]. For example,

// returns [100 => ['id' => 100, 'username' => '...', ...], 101 => [...], 103 => [...], ...]
$query = (new \yii\db\Query())
    ->from('user')
    ->limit(10)
    ->indexBy('id')
    ->all();

To index by expression values, pass an anonymous function to the [[yii\db\Query::indexBy()|indexBy()]] method:

$query = (new \yii\db\Query())
    ->from('user')
    ->indexBy(function ($row) {
        return $row['id'] . $row['username'];
    })->all();

The anonymous function takes a parameter $row which contains the current row data and should return a scalar value which will be used as the index value for the current row.

Batch Query

When working with large amounts of data, methods such as [[yii\db\Query::all()]] are not suitable because they require loading all data into the memory. To keep the memory requirement low, Yii provides the so-called batch query support. A batch query makes use of the data cursor and fetches data in batches.

Batch query can be used like the following:

use yii\db\Query;

$query = (new Query())
    ->from('user')
    ->orderBy('id');

foreach ($query->batch() as $users) {
    // $users is an array of 100 or fewer rows from the user table
}

// or if you want to iterate the row one by one
foreach ($query->each() as $user) {
    // $user represents one row of data from the user table
}

The method [[yii\db\Query::batch()]] and [[yii\db\Query::each()]] return an [[yii\db\BatchQueryResult]] object which implements the Iterator interface and thus can be used in the foreach construct. During the first iteration, a SQL query is made to the database. Data are then fetched in batches in the remaining iterations. By default, the batch size is 100, meaning 100 rows of data are being fetched in each batch. You can change the batch size by passing the first parameter to the batch() or each() method.

Compared to the [[yii\db\Query::all()]], the batch query only loads 100 rows of data at a time into the memory. If you process the data and then discard it right away, the batch query can help reduce memory usage.

If you specify the query result to be indexed by some column via [[yii\db\Query::indexBy()]], the batch query will still keep the proper index. For example,

$query = (new \yii\db\Query())
    ->from('user')
    ->indexBy('username');

foreach ($query->batch() as $users) {
    // $users is indexed by the "username" column
}

foreach ($query->each() as $username => $user) {
}