5.7.3 Query Attribute User-Defined Functions

• mysql_query_attribute_string(name)

  Applications can define attributes that apply to the next query sent to the server. The mysql_query_attribute_string() function, available as of MySQL 8.0.23, returns an attribute value as a string, given the attribute name. This function enables a query to access and incorporate values of the attributes that apply to it.

  mysql_query_attribute_string() is installed by installing the query_attributes component. See Section 9.6, “Query Attributes”, which also discusses the purpose and use of query attributes.

  Arguments:

  • name: The attribute name.

  Return value:

  Returns the attribute value as a string for success, or NULL if the attribute does not exist.

  Example:

  The following example uses the mysql client query_attributes command to define query attributes that can be retrieved by mysql_query_attribute_string(). The SELECT shows that retrieving a nonexistent attribute (n3) returns NULL.

  mysql> query_attributes n1 v1 n2 v2;
  mysql> SELECT
      ->   mysql_query_attribute_string('n1') AS 'attr 1',
      ->   mysql_query_attribute_string('n2') AS 'attr 2',
      ->   mysql_query_attribute_string('n3') AS 'attr 3';
  +--------+--------+--------+
  | attr 1 | attr 2 | attr 3 |
  +--------+--------+--------+
  | v1     | v2     | NULL   |
  +--------+--------+--------+

  For additional examples, see Section 9.6, “Query Attributes”.