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Fixed bug#19862: Sort with filesort by function evaluates function twice

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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.
This commit is contained in:
evgen@moonbone.local
2006-07-26 00:31:29 +04:00
parent 8b7fc77a0f
commit 4ee2e07cc0
8 changed files with 81 additions and 1 deletions
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6
mysql-test/r/udf.result
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@@ -93,6 +93,12 @@ NULL
0R
FR
DROP TABLE bug19904;
create table t1(f1 int);
insert into t1 values(1),(2);
explain select myfunc_int(f1) from t1 order by 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 2 Using temporary; Using filesort
drop table t1;
End of 5.0 tests.
DROP FUNCTION metaphon;
DROP FUNCTION myfunc_double;