WP_Meta_Query()

Core class used to implement meta queries for the Meta API.


Description Description

Used for generating SQL clauses that filter a primary query according to metadata keys and values.

WP_Meta_Query is a helper that allows primary query classes, such as WP_Query and WP_User_Query,

to filter their results by object metadata, by generating JOIN and WHERE subclauses to be attached to the primary SQL query string.


Source Source

File: wp-includes/class-wp-meta-query.php

class WP_Meta_Query {
	/**
	 * Array of metadata queries.
	 *
	 * See WP_Meta_Query::__construct() for information on meta query arguments.
	 *
	 * @since 3.2.0
	 * @access public
	 * @var array
	 */
	public $queries = array();

	/**
	 * The relation between the queries. Can be one of 'AND' or 'OR'.
	 *
	 * @since 3.2.0
	 * @access public
	 * @var string
	 */
	public $relation;

	/**
	 * Database table to query for the metadata.
	 *
	 * @since 4.1.0
	 * @access public
	 * @var string
	 */
	public $meta_table;

	/**
	 * Column in meta_table that represents the ID of the object the metadata belongs to.
	 *
	 * @since 4.1.0
	 * @access public
	 * @var string
	 */
	public $meta_id_column;

	/**
	 * Database table that where the metadata's objects are stored (eg $wpdb->users).
	 *
	 * @since 4.1.0
	 * @access public
	 * @var string
	 */
	public $primary_table;

	/**
	 * Column in primary_table that represents the ID of the object.
	 *
	 * @since 4.1.0
	 * @access public
	 * @var string
	 */
	public $primary_id_column;

	/**
	 * A flat list of table aliases used in JOIN clauses.
	 *
	 * @since 4.1.0
	 * @access protected
	 * @var array
	 */
	protected $table_aliases = array();

	/**
	 * A flat list of clauses, keyed by clause 'name'.
	 *
	 * @since 4.2.0
	 * @access protected
	 * @var array
	 */
	protected $clauses = array();

	/**
	 * Whether the query contains any OR relations.
	 *
	 * @since 4.3.0
	 * @access protected
	 * @var bool
	 */
	protected $has_or_relation = false;

	/**
	 * Constructor.
	 *
	 * @since 3.2.0
	 * @since 4.2.0 Introduced support for naming query clauses by associative array keys.
	 *
	 * @access public
	 *
	 * @param array $meta_query {
	 *     Array of meta query clauses. When first-order clauses or sub-clauses use strings as
	 *     their array keys, they may be referenced in the 'orderby' parameter of the parent query.
	 *
	 *     @type string $relation Optional. The MySQL keyword used to join
	 *                            the clauses of the query. Accepts 'AND', or 'OR'. Default 'AND'.
	 *     @type array {
	 *         Optional. An array of first-order clause parameters, or another fully-formed meta query.
	 *
	 *         @type string $key     Meta key to filter by.
	 *         @type string $value   Meta value to filter by.
	 *         @type string $compare MySQL operator used for comparing the $value. Accepts '=',
	 *                               '!=', '>', '>=', '<', '<=', 'LIKE', 'NOT LIKE',
	 *                               'IN', 'NOT IN', 'BETWEEN', 'NOT BETWEEN', 'REGEXP',
	 *                               'NOT REGEXP', 'RLIKE', 'EXISTS' or 'NOT EXISTS'.
	 *                               Default is 'IN' when `$value` is an array, '=' otherwise.
	 *         @type string $type    MySQL data type that the meta_value column will be CAST to for
	 *                               comparisons. Accepts 'NUMERIC', 'BINARY', 'CHAR', 'DATE',
	 *                               'DATETIME', 'DECIMAL', 'SIGNED', 'TIME', or 'UNSIGNED'.
	 *                               Default is 'CHAR'.
	 *     }
	 * }
	 */
	public function __construct( $meta_query = false ) {
		if ( !$meta_query )
			return;

		if ( isset( $meta_query['relation'] ) && strtoupper( $meta_query['relation'] ) == 'OR' ) {
			$this->relation = 'OR';
		} else {
			$this->relation = 'AND';
		}

		$this->queries = $this->sanitize_query( $meta_query );
	}

	/**
	 * Ensure the 'meta_query' argument passed to the class constructor is well-formed.
	 *
	 * Eliminates empty items and ensures that a 'relation' is set.
	 *
	 * @since 4.1.0
	 * @access public
	 *
	 * @param array $queries Array of query clauses.
	 * @return array Sanitized array of query clauses.
	 */
	public function sanitize_query( $queries ) {
		$clean_queries = array();

		if ( ! is_array( $queries ) ) {
			return $clean_queries;
		}

		foreach ( $queries as $key => $query ) {
			if ( 'relation' === $key ) {
				$relation = $query;

			} elseif ( ! is_array( $query ) ) {
				continue;

			// First-order clause.
			} elseif ( $this->is_first_order_clause( $query ) ) {
				if ( isset( $query['value'] ) && array() === $query['value'] ) {
					unset( $query['value'] );
				}

				$clean_queries[ $key ] = $query;

			// Otherwise, it's a nested query, so we recurse.
			} else {
				$cleaned_query = $this->sanitize_query( $query );

				if ( ! empty( $cleaned_query ) ) {
					$clean_queries[ $key ] = $cleaned_query;
				}
			}
		}

		if ( empty( $clean_queries ) ) {
			return $clean_queries;
		}

		// Sanitize the 'relation' key provided in the query.
		if ( isset( $relation ) && 'OR' === strtoupper( $relation ) ) {
			$clean_queries['relation'] = 'OR';
			$this->has_or_relation = true;

		/*
		 * If there is only a single clause, call the relation 'OR'.
		 * This value will not actually be used to join clauses, but it
		 * simplifies the logic around combining key-only queries.
		 */
		} elseif ( 1 === count( $clean_queries ) ) {
			$clean_queries['relation'] = 'OR';

		// Default to AND.
		} else {
			$clean_queries['relation'] = 'AND';
		}

		return $clean_queries;
	}

	/**
	 * Determine whether a query clause is first-order.
	 *
	 * A first-order meta query clause is one that has either a 'key' or
	 * a 'value' array key.
	 *
	 * @since 4.1.0
	 * @access protected
	 *
	 * @param array $query Meta query arguments.
	 * @return bool Whether the query clause is a first-order clause.
	 */
	protected function is_first_order_clause( $query ) {
		return isset( $query['key'] ) || isset( $query['value'] );
	}

	/**
	 * Constructs a meta query based on 'meta_*' query vars
	 *
	 * @since 3.2.0
	 * @access public
	 *
	 * @param array $qv The query variables
	 */
	public function parse_query_vars( $qv ) {
		$meta_query = array();

		/*
		 * For orderby=meta_value to work correctly, simple query needs to be
		 * first (so that its table join is against an unaliased meta table) and
		 * needs to be its own clause (so it doesn't interfere with the logic of
		 * the rest of the meta_query).
		 */
		$primary_meta_query = array();
		foreach ( array( 'key', 'compare', 'type' ) as $key ) {
			if ( ! empty( $qv[ "meta_$key" ] ) ) {
				$primary_meta_query[ $key ] = $qv[ "meta_$key" ];
			}
		}

		// WP_Query sets 'meta_value' = '' by default.
		if ( isset( $qv['meta_value'] ) && '' !== $qv['meta_value'] && ( ! is_array( $qv['meta_value'] ) || $qv['meta_value'] ) ) {
			$primary_meta_query['value'] = $qv['meta_value'];
		}

		$existing_meta_query = isset( $qv['meta_query'] ) && is_array( $qv['meta_query'] ) ? $qv['meta_query'] : array();

		if ( ! empty( $primary_meta_query ) && ! empty( $existing_meta_query ) ) {
			$meta_query = array(
				'relation' => 'AND',
				$primary_meta_query,
				$existing_meta_query,
			);
		} elseif ( ! empty( $primary_meta_query ) ) {
			$meta_query = array(
				$primary_meta_query,
			);
		} elseif ( ! empty( $existing_meta_query ) ) {
			$meta_query = $existing_meta_query;
		}

		$this->__construct( $meta_query );
	}

	/**
	 * Return the appropriate alias for the given meta type if applicable.
	 *
	 * @since 3.7.0
	 * @access public
	 *
	 * @param string $type MySQL type to cast meta_value.
	 * @return string MySQL type.
	 */
	public function get_cast_for_type( $type = '' ) {
		if ( empty( $type ) )
			return 'CHAR';

		$meta_type = strtoupper( $type );

		if ( ! preg_match( '/^(?:BINARY|CHAR|DATE|DATETIME|SIGNED|UNSIGNED|TIME|NUMERIC(?:\(\d+(?:,\s?\d+)?\))?|DECIMAL(?:\(\d+(?:,\s?\d+)?\))?)$/', $meta_type ) )
			return 'CHAR';

		if ( 'NUMERIC' == $meta_type )
			$meta_type = 'SIGNED';

		return $meta_type;
	}

	/**
	 * Generates SQL clauses to be appended to a main query.
	 *
	 * @since 3.2.0
	 * @access public
	 *
	 * @param string $type              Type of meta, eg 'user', 'post'.
	 * @param string $primary_table     Database table where the object being filtered is stored (eg wp_users).
	 * @param string $primary_id_column ID column for the filtered object in $primary_table.
	 * @param object $context           Optional. The main query object.
	 * @return false|array {
	 *     Array containing JOIN and WHERE SQL clauses to append to the main query.
	 *
	 *     @type string $join  SQL fragment to append to the main JOIN clause.
	 *     @type string $where SQL fragment to append to the main WHERE clause.
	 * }
	 */
	public function get_sql( $type, $primary_table, $primary_id_column, $context = null ) {
		if ( ! $meta_table = _get_meta_table( $type ) ) {
			return false;
		}

		$this->table_aliases = array();

		$this->meta_table     = $meta_table;
		$this->meta_id_column = sanitize_key( $type . '_id' );

		$this->primary_table     = $primary_table;
		$this->primary_id_column = $primary_id_column;

		$sql = $this->get_sql_clauses();

		/*
		 * If any JOINs are LEFT JOINs (as in the case of NOT EXISTS), then all JOINs should
		 * be LEFT. Otherwise posts with no metadata will be excluded from results.
		 */
		if ( false !== strpos( $sql['join'], 'LEFT JOIN' ) ) {
			$sql['join'] = str_replace( 'INNER JOIN', 'LEFT JOIN', $sql['join'] );
		}

		/**
		 * Filters the meta query's generated SQL.
		 *
		 * @since 3.1.0
		 *
		 * @param array  $clauses           Array containing the query's JOIN and WHERE clauses.
		 * @param array  $queries           Array of meta queries.
		 * @param string $type              Type of meta.
		 * @param string $primary_table     Primary table.
		 * @param string $primary_id_column Primary column ID.
		 * @param object $context           The main query object.
		 */
		return apply_filters_ref_array( 'get_meta_sql', array( $sql, $this->queries, $type, $primary_table, $primary_id_column, $context ) );
	}

	/**
	 * Generate SQL clauses to be appended to a main query.
	 *
	 * Called by the public WP_Meta_Query::get_sql(), this method is abstracted
	 * out to maintain parity with the other Query classes.
	 *
	 * @since 4.1.0
	 * @access protected
	 *
	 * @return array {
	 *     Array containing JOIN and WHERE SQL clauses to append to the main query.
	 *
	 *     @type string $join  SQL fragment to append to the main JOIN clause.
	 *     @type string $where SQL fragment to append to the main WHERE clause.
	 * }
	 */
	protected function get_sql_clauses() {
		/*
		 * $queries are passed by reference to get_sql_for_query() for recursion.
		 * To keep $this->queries unaltered, pass a copy.
		 */
		$queries = $this->queries;
		$sql = $this->get_sql_for_query( $queries );

		if ( ! empty( $sql['where'] ) ) {
			$sql['where'] = ' AND ' . $sql['where'];
		}

		return $sql;
	}

	/**
	 * Generate SQL clauses for a single query array.
	 *
	 * If nested subqueries are found, this method recurses the tree to
	 * produce the properly nested SQL.
	 *
	 * @since 4.1.0
	 * @access protected
	 *
	 * @param array $query Query to parse, passed by reference.
	 * @param int   $depth Optional. Number of tree levels deep we currently are.
	 *                     Used to calculate indentation. Default 0.
	 * @return array {
	 *     Array containing JOIN and WHERE SQL clauses to append to a single query array.
	 *
	 *     @type string $join  SQL fragment to append to the main JOIN clause.
	 *     @type string $where SQL fragment to append to the main WHERE clause.
	 * }
	 */
	protected function get_sql_for_query( &$query, $depth = 0 ) {
		$sql_chunks = array(
			'join'  => array(),
			'where' => array(),
		);

		$sql = array(
			'join'  => '',
			'where' => '',
		);

		$indent = '';
		for ( $i = 0; $i < $depth; $i++ ) {
			$indent .= "  ";
		}

		foreach ( $query as $key => &$clause ) {
			if ( 'relation' === $key ) {
				$relation = $query['relation'];
			} elseif ( is_array( $clause ) ) {

				// This is a first-order clause.
				if ( $this->is_first_order_clause( $clause ) ) {
					$clause_sql = $this->get_sql_for_clause( $clause, $query, $key );

					$where_count = count( $clause_sql['where'] );
					if ( ! $where_count ) {
						$sql_chunks['where'][] = '';
					} elseif ( 1 === $where_count ) {
						$sql_chunks['where'][] = $clause_sql['where'][0];
					} else {
						$sql_chunks['where'][] = '( ' . implode( ' AND ', $clause_sql['where'] ) . ' )';
					}

					$sql_chunks['join'] = array_merge( $sql_chunks['join'], $clause_sql['join'] );
				// This is a subquery, so we recurse.
				} else {
					$clause_sql = $this->get_sql_for_query( $clause, $depth + 1 );

					$sql_chunks['where'][] = $clause_sql['where'];
					$sql_chunks['join'][]  = $clause_sql['join'];
				}
			}
		}

		// Filter to remove empties.
		$sql_chunks['join']  = array_filter( $sql_chunks['join'] );
		$sql_chunks['where'] = array_filter( $sql_chunks['where'] );

		if ( empty( $relation ) ) {
			$relation = 'AND';
		}

		// Filter duplicate JOIN clauses and combine into a single string.
		if ( ! empty( $sql_chunks['join'] ) ) {
			$sql['join'] = implode( ' ', array_unique( $sql_chunks['join'] ) );
		}

		// Generate a single WHERE clause with proper brackets and indentation.
		if ( ! empty( $sql_chunks['where'] ) ) {
			$sql['where'] = '( ' . "\n  " . $indent . implode( ' ' . "\n  " . $indent . $relation . ' ' . "\n  " . $indent, $sql_chunks['where'] ) . "\n" . $indent . ')';
		}

		return $sql;
	}

	/**
	 * Generate SQL JOIN and WHERE clauses for a first-order query clause.
	 *
	 * "First-order" means that it's an array with a 'key' or 'value'.
	 *
	 * @since 4.1.0
	 * @access public
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @param array  $clause       Query clause, passed by reference.
	 * @param array  $parent_query Parent query array.
	 * @param string $clause_key   Optional. The array key used to name the clause in the original `$meta_query`
	 *                             parameters. If not provided, a key will be generated automatically.
	 * @return array {
	 *     Array containing JOIN and WHERE SQL clauses to append to a first-order query.
	 *
	 *     @type string $join  SQL fragment to append to the main JOIN clause.
	 *     @type string $where SQL fragment to append to the main WHERE clause.
	 * }
	 */
	public function get_sql_for_clause( &$clause, $parent_query, $clause_key = '' ) {
		global $wpdb;

		$sql_chunks = array(
			'where' => array(),
			'join' => array(),
		);

		if ( isset( $clause['compare'] ) ) {
			$clause['compare'] = strtoupper( $clause['compare'] );
		} else {
			$clause['compare'] = isset( $clause['value'] ) && is_array( $clause['value'] ) ? 'IN' : '=';
		}

		if ( ! in_array( $clause['compare'], array(
			'=', '!=', '>', '>=', '<', '<=',
			'LIKE', 'NOT LIKE',
			'IN', 'NOT IN',
			'BETWEEN', 'NOT BETWEEN',
			'EXISTS', 'NOT EXISTS',
			'REGEXP', 'NOT REGEXP', 'RLIKE'
		) ) ) {
			$clause['compare'] = '=';
		}

		$meta_compare = $clause['compare'];

		// First build the JOIN clause, if one is required.
		$join = '';

		// We prefer to avoid joins if possible. Look for an existing join compatible with this clause.
		$alias = $this->find_compatible_table_alias( $clause, $parent_query );
		if ( false === $alias ) {
			$i = count( $this->table_aliases );
			$alias = $i ? 'mt' . $i : $this->meta_table;

			// JOIN clauses for NOT EXISTS have their own syntax.
			if ( 'NOT EXISTS' === $meta_compare ) {
				$join .= " LEFT JOIN $this->meta_table";
				$join .= $i ? " AS $alias" : '';
				$join .= $wpdb->prepare( " ON ($this->primary_table.$this->primary_id_column = $alias.$this->meta_id_column AND $alias.meta_key = %s )", $clause['key'] );

			// All other JOIN clauses.
			} else {
				$join .= " INNER JOIN $this->meta_table";
				$join .= $i ? " AS $alias" : '';
				$join .= " ON ( $this->primary_table.$this->primary_id_column = $alias.$this->meta_id_column )";
			}

			$this->table_aliases[] = $alias;
			$sql_chunks['join'][] = $join;
		}

		// Save the alias to this clause, for future siblings to find.
		$clause['alias'] = $alias;

		// Determine the data type.
		$_meta_type = isset( $clause['type'] ) ? $clause['type'] : '';
		$meta_type  = $this->get_cast_for_type( $_meta_type );
		$clause['cast'] = $meta_type;

		// Fallback for clause keys is the table alias. Key must be a string.
		if ( is_int( $clause_key ) || ! $clause_key ) {
			$clause_key = $clause['alias'];
		}

		// Ensure unique clause keys, so none are overwritten.
		$iterator = 1;
		$clause_key_base = $clause_key;
		while ( isset( $this->clauses[ $clause_key ] ) ) {
			$clause_key = $clause_key_base . '-' . $iterator;
			$iterator++;
		}

		// Store the clause in our flat array.
		$this->clauses[ $clause_key ] =& $clause;

		// Next, build the WHERE clause.

		// meta_key.
		if ( array_key_exists( 'key', $clause ) ) {
			if ( 'NOT EXISTS' === $meta_compare ) {
				$sql_chunks['where'][] = $alias . '.' . $this->meta_id_column . ' IS NULL';
			} else {
				$sql_chunks['where'][] = $wpdb->prepare( "$alias.meta_key = %s", trim( $clause['key'] ) );
			}
		}

		// meta_value.
		if ( array_key_exists( 'value', $clause ) ) {
			$meta_value = $clause['value'];

			if ( in_array( $meta_compare, array( 'IN', 'NOT IN', 'BETWEEN', 'NOT BETWEEN' ) ) ) {
				if ( ! is_array( $meta_value ) ) {
					$meta_value = preg_split( '/[,\s]+/', $meta_value );
				}
			} else {
				$meta_value = trim( $meta_value );
			}

			switch ( $meta_compare ) {
				case 'IN' :
				case 'NOT IN' :
					$meta_compare_string = '(' . substr( str_repeat( ',%s', count( $meta_value ) ), 1 ) . ')';
					$where = $wpdb->prepare( $meta_compare_string, $meta_value );
					break;

				case 'BETWEEN' :
				case 'NOT BETWEEN' :
					$meta_value = array_slice( $meta_value, 0, 2 );
					$where = $wpdb->prepare( '%s AND %s', $meta_value );
					break;

				case 'LIKE' :
				case 'NOT LIKE' :
					$meta_value = '%' . $wpdb->esc_like( $meta_value ) . '%';
					$where = $wpdb->prepare( '%s', $meta_value );
					break;

				// EXISTS with a value is interpreted as '='.
				case 'EXISTS' :
					$meta_compare = '=';
					$where = $wpdb->prepare( '%s', $meta_value );
					break;

				// 'value' is ignored for NOT EXISTS.
				case 'NOT EXISTS' :
					$where = '';
					break;

				default :
					$where = $wpdb->prepare( '%s', $meta_value );
					break;

			}

			if ( $where ) {
				if ( 'CHAR' === $meta_type ) {
					$sql_chunks['where'][] = "$alias.meta_value {$meta_compare} {$where}";
				} else {
					$sql_chunks['where'][] = "CAST($alias.meta_value AS {$meta_type}) {$meta_compare} {$where}";
				}
			}
		}

		/*
		 * Multiple WHERE clauses (for meta_key and meta_value) should
		 * be joined in parentheses.
		 */
		if ( 1 < count( $sql_chunks['where'] ) ) {
			$sql_chunks['where'] = array( '( ' . implode( ' AND ', $sql_chunks['where'] ) . ' )' );
		}

		return $sql_chunks;
	}

	/**
	 * Get a flattened list of sanitized meta clauses.
	 *
	 * This array should be used for clause lookup, as when the table alias and CAST type must be determined for
	 * a value of 'orderby' corresponding to a meta clause.
	 *
	 * @since 4.2.0
	 * @access public
	 *
	 * @return array Meta clauses.
	 */
	public function get_clauses() {
		return $this->clauses;
	}

	/**
	 * Identify an existing table alias that is compatible with the current
	 * query clause.
	 *
	 * We avoid unnecessary table joins by allowing each clause to look for
	 * an existing table alias that is compatible with the query that it
	 * needs to perform.
	 *
	 * An existing alias is compatible if (a) it is a sibling of `$clause`
	 * (ie, it's under the scope of the same relation), and (b) the combination
	 * of operator and relation between the clauses allows for a shared table join.
	 * In the case of WP_Meta_Query, this only applies to 'IN' clauses that are
	 * connected by the relation 'OR'.
	 *
	 * @since 4.1.0
	 * @access protected
	 *
	 * @param  array       $clause       Query clause.
	 * @param  array       $parent_query Parent query of $clause.
	 * @return string|bool Table alias if found, otherwise false.
	 */
	protected function find_compatible_table_alias( $clause, $parent_query ) {
		$alias = false;

		foreach ( $parent_query as $sibling ) {
			// If the sibling has no alias yet, there's nothing to check.
			if ( empty( $sibling['alias'] ) ) {
				continue;
			}

			// We're only interested in siblings that are first-order clauses.
			if ( ! is_array( $sibling ) || ! $this->is_first_order_clause( $sibling ) ) {
				continue;
			}

			$compatible_compares = array();

			// Clauses connected by OR can share joins as long as they have "positive" operators.
			if ( 'OR' === $parent_query['relation'] ) {
				$compatible_compares = array( '=', 'IN', 'BETWEEN', 'LIKE', 'REGEXP', 'RLIKE', '>', '>=', '<', '<=' );

			// Clauses joined by AND with "negative" operators share a join only if they also share a key.
			} elseif ( isset( $sibling['key'] ) && isset( $clause['key'] ) && $sibling['key'] === $clause['key'] ) {
				$compatible_compares = array( '!=', 'NOT IN', 'NOT LIKE' );
			}

			$clause_compare  = strtoupper( $clause['compare'] );
			$sibling_compare = strtoupper( $sibling['compare'] );
			if ( in_array( $clause_compare, $compatible_compares ) && in_array( $sibling_compare, $compatible_compares ) ) {
				$alias = $sibling['alias'];
				break;
			}
		}

		/**
		 * Filters the table alias identified as compatible with the current clause.
		 *
		 * @since 4.1.0
		 *
		 * @param string|bool $alias        Table alias, or false if none was found.
		 * @param array       $clause       First-order query clause.
		 * @param array       $parent_query Parent of $clause.
		 * @param object      $this         WP_Meta_Query object.
		 */
		return apply_filters( 'meta_query_find_compatible_table_alias', $alias, $clause, $parent_query, $this ) ;
	}

	/**
	 * Checks whether the current query has any OR relations.
	 *
	 * In some cases, the presence of an OR relation somewhere in the query will require
	 * the use of a `DISTINCT` or `GROUP BY` keyword in the `SELECT` clause. The current
	 * method can be used in these cases to determine whether such a clause is necessary.
	 *
	 * @since 4.3.0
	 *
	 * @return bool True if the query contains any `OR` relations, otherwise false.
	 */
	public function has_or_relation() {
		return $this->has_or_relation;
	}
}

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Version Description
3.2.0 Introduced.

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User Contributed Notes User Contributed Notes

  1. Skip to note content
    Contributed by Sagar Prajapati

    In this case, you pass an array of key/value pair arrays (which were described above in the meta_query argument).

    You can optionally pass the `relation` key and set it to either OR or AND. It defines the relation, when there is more than one meta query (whether all of the conditions should be met, or at least one of them needs to be met).

    Nested arrays can be used to construct complex queries. For example, where _my_custom_key = value OR (_my_custom_key_2 = value AND _my_custom_key_3 = value).

    $meta_query_args = array(
    	'relation' => 'OR', // Optional, defaults to "AND"
    	array(
    		'key'     => '_my_custom_key',
    		'value'   => 'Value I am looking for',
    		'compare' => '='
    	),
    	array(
    		'relation' => 'AND',
    		array(
    			'key'     => '_my_custom_key_2',
    			'value'   => 'Value I am looking for 2',
    			'compare' => '='
    		),
    		array(
    			'key'     => '_my_custom_key_3',
    			'value'   => 'Value I am looking for 3',
    			'compare' => '='
    		)
    	)
    );
    $meta_query = new WP_Meta_Query( $meta_query_args );
    
  2. Skip to note content
    Contributed by Sagar Prajapati

    Using the WP_Meta_Query::parse_query_vars( $query ) method: You can use this method, if you want to use the simple query args(`meta_key`, `meta_value`, `meta_type`, `meta_compare`), or if you are unsure of the presence of meta query parameters.

    // $query_vars can have various contents, so an example is not added here, but you need to have it defined beforehand
    $meta_query = new WP_Meta_Query();
    // Won't work with an array( 'relation', array( 'key' => '...' ) )
    // as the parse_query_vars() method searches for the `meta_` prefix
    $meta_query->parse_query_vars( array(
    	'meta_key' => 'some_key',
    	// etc.
    ) );
    
  3. Skip to note content
    Contributed by Sagar Prajapati

    Getting the final SQL

    You can retrieve the generated SQL by using the following method.

    $mq_sql = $meta_query->get_sql(
    	$type,
    	$primary_table,
    	$primary_id_column,
    	$context = null
    );
    

    List of Arguments:

  4. $type’ (string) – Type of meta(post, comment, user).
  5. $primary_table (string) – The table where we will be looking for rows. You can pass for instance $wpdb->posts, or the alias name if you are aliasing the table in your SQL query
  6. $primary_id_column (string) – The column that holds the ID(for posts, it is ID, for comments it is comment_ID and for users is ID).
  7. $context (object) – Optional – The main query object. It is only used when the result is passed to the get_meta_sql filter.
  8. On failure(for instance – lacking any meta query parameters in the query array), this function will return `false`.

    On success, it will return an array like this:

    array(
    	'join'  => $join_sql,
    	'where' => $where_sql
    )
    

    With each key holding the SQL for the corresponding section.

  9. Skip to note content
    Contributed by Sagar Prajapati

    Example: Single Meta Entry – Flat array

    Query

    // Note that this will produce a "key only" query
    // If you want a full one, add a meta_value and meta_compare array key/value pair
    $query_args = array(
    	'meta_key' => 'some_key_name',
    );
    $meta_query = new WP_Meta_Query();
    $meta_query->parse_query_vars( $query_args );
    $mq = $meta_query->get_sql(
    	'post',
    	$wpdb->posts,
    	'ID',
    	null
    );
    

    Result

    array (size=2)
      'join' => string ' INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)' (length=62)
      'where' => string ' AND (wp_postmeta.meta_key = 'some_key' )' (length=40)
    
  10. Skip to note content
    Contributed by Sagar Prajapati

    Example: Multiple Meta Entries – Multi dimensional array:

    Query:

    $query_args = array( 'meta_query' => array(
    	'relation' => 'OR',
    	array(
    		'key' => 'foo_key',
    		// 'value' => 'foo',
    		// 'compare' => 'LIKE',
    	),
    	array(
    		'key' => 'bar_key',
    	),
    ) );
    $meta_query = new WP_Meta_Query();
    $meta_query->parse_query_vars( $query_args );
    $mq_sql = $meta_query->get_sql(
    	'post',
    	$wpdb->posts,
    	'ID',
    	null
    );
    

    Result:

    'join' => string ' INNER JOIN wp_postmeta ON wp_posts.ID = wp_postmeta.post_id' (length=60)
    'where' => string ' AND (wp_postmeta.meta_key = 'foo_key' OR wp_postmeta.meta_key = 'bar_key' )' (length=75)
    

    Note: This example will not append a space to the join statement, so you have to do it manually to not crash your query. The same goes for the where statement.

    If you’re using the value and compare parts of the meta_query input argument array, then the query string will look something like the following:

    'where' => string ' AND (wp_postmeta.meta_key = 'foo_key' OR  (mt1.meta_key = 'bar_key' AND CAST(mt1.meta_value AS CHAR) LIKE '%foo%') )'
    

    Keep in mind that mt1 is the alias of the meta table and the join clause will look something like this and therefore use the JOIN twice:

    'join' => string ' INNER JOIN wp_postmeta ON wp_posts.ID = wp_postmeta.post_id INNER JOIN wp_postmeta AS mt1 ON (wp_posts.ID = mt1.post_id)'
    

    Use that in further queries or form inside your posts_clauses, posts_where or posts_join filter callbacks.

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