WP_Tax_Query::get_sql_for_clause()
Method: Generates SQL JOIN and WHERE clauses for a “first-order” query clause.
Source: wp-includes/class-wp-tax-query.php:384
WP_Tax_Query::find_compatible_table_alias()
Method: Identifies an existing table alias that is compatible with the current query clause.
Source: wp-includes/class-wp-tax-query.php:505