• evgen@moonbone.local's avatar
    Fixed bug#19862: Sort with filesort by function evaluates function twice · 4ee2e07c
    evgen@moonbone.local authored
    When there is no index defined filesort is used to sort the result of a
    query. If there is a function in the select list and the result set should be
    ordered by it's value then this function will be evaluated twice. First time to
    get the value of the sort key and second time to send its value to a user.
    This happens because filesort when sorts a table remembers only values of its
    fields but not values of functions.
    All functions are affected. But taking into account that SP and UDF functions
    can be both expensive and non-deterministic a temporary table should be used 
    to store their results and then sort it to avoid twice SP evaluation and to 
    get a correct result.
    
    If an expression referenced in an ORDER clause contains a SP or UDF 
    function, force the use of a temporary table.
    
    A new Item_processor function called func_type_checker_processor is added
    to check whether the expression contains a function of a particular type.
    4ee2e07c
item_func.h 39.4 KB