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Fix bug lp:1009187, mdev-373, mysql bug#58628

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Analysis:
The queries in question use the [unique | index]_subquery execution methods.
These methods reuse the ref keys constructed by create_ref_for_key(). The
way create_ref_for_key() works is that it doesn't store in ref.key_copy[]
store_key elements that represent constants. In particular it doesn't store
the store_key for NULL constants.

The execution of [unique | index]_subquery calls
subselect_uniquesubquery_engine::copy_ref_key, which in addition to copy
the left IN argument into a index lookup key, is supposed to detect if
the left IN argument contains NULLs. Since the store_key for the NULL
constant is not copied into the key array, the null is not detected, and
execution erroneously proceeds as if it should look for a complete match.

Solution:
The solution (unlike MySQL) is to reuse already computed information about
NULL presence. Item_in_optimizer::val_int already finds out if the left IN
operand contains NULLs. The fix propagates this to the execution methods
subselect_[unique | index]subquery_engine::exec so it knows if there were
NULL values independent of the presence of keys.

In addition the patch siplifies copy_ref_key() and the logic that hanldes
the case of NULLs in the left IN operand.
This commit is contained in:
unknown 2012-09-14 11:26:01 +03:00
commit b917fb63a6
4 changed files with 180 additions and 86 deletions
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2
sql/item_subselect.h
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@ -334,6 +334,7 @@ public:
bool test_limit(st_select_lex_unit *unit);
virtual void print(String *str, enum_query_type query_type);
bool fix_fields(THD *thd, Item **ref);
inline bool left_expr_has_null();
friend class Item_ref_null_helper;
friend class Item_is_not_null_test;
@ -513,7 +514,6 @@ protected:
expression is NULL.
*/
bool empty_result_set;
bool null_keypart; /* TRUE <=> constructed search tuple has a NULL */
public:
// constructor can assign THD because it will be called after JOIN::prepare