diff options
Diffstat (limited to 'sql/item_func.h')
| -rw-r--r-- | sql/item_func.h | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/sql/item_func.h b/sql/item_func.h index 629d0dbfdbc..e09b584de95 100644 --- a/sql/item_func.h +++ b/sql/item_func.h @@ -1022,6 +1022,56 @@ public: fixed= 1; return res; } + void update_used_tables() + { + /* + TODO: Make a member in UDF_INIT and return if a UDF is deterministic or + not. + Currently UDF_INIT has a member (const_item) that is an in/out + parameter to the init() call. + The code in udf_handler::fix_fields also duplicates the arguments + handling code in Item_func::fix_fields(). + + The lack of information if a UDF is deterministic makes writing + a correct update_used_tables() for UDFs impossible. + One solution to this would be : + - Add a is_deterministic member of UDF_INIT + - (optionally) deprecate the const_item member of UDF_INIT + - Take away the duplicate code from udf_handler::fix_fields() and + make Item_udf_func call Item_func::fix_fields() to process its + arguments as for any other function. + - Store the deterministic flag returned by <udf>_init into the + udf_handler. + - Don't implement Item_udf_func::fix_fields, implement + Item_udf_func::fix_length_and_dec() instead (similar to non-UDF + functions). + - Override Item_func::update_used_tables to call + Item_func::update_used_tables() and add a RAND_TABLE_BIT to the + result of Item_func::update_used_tables() if the UDF is + non-deterministic. + - (optionally) rename RAND_TABLE_BIT to NONDETERMINISTIC_BIT to + better describe its usage. + + The above would require a change of the UDF API. + Until that change is done here's how the current code works: + We call Item_func::update_used_tables() only when we know that + the function depends on real non-const tables and is deterministic. + This can be done only because we know that the optimizer will + call update_used_tables() only when there's possibly a new const + table. So update_used_tables() can only make a Item_func more + constant than it is currently. + That's why we don't need to do anything if a function is guaranteed + to return non-constant (it's non-deterministic) or is already a + const. + */ + if ((used_tables_cache & ~PSEUDO_TABLE_BITS) && + !(used_tables_cache & RAND_TABLE_BIT)) + { + Item_func::update_used_tables(); + if (!const_item_cache && !used_tables_cache) + used_tables_cache= RAND_TABLE_BIT; + } + } void cleanup(); Item_result result_type () const { return udf.result_type(); } table_map not_null_tables() const { return 0; } |