MySQL 9.0.0
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27class Func_ptr;
28class Item;
29class Item_field;
30template <class T>
31class Mem_root_array;
32class THD;
36 Return a new item that is to be used after materialization (as given by
37 items_to_copy). There are three main cases:
39 1. The item isn't touched by materialization (e.g., because it's constant,
40 or because we're not ready to compute it yet).
41 2. The item is directly in the items_to_copy list, so it has its own field
42 in the resulting temporary table; the corresponding new Item_field
43 is returned.
44 3. A _part_ of the item is in the items_to_copy list; e.g. say that we
45 have an item (t1.x + 1), and t1.x is materialized into <temporary>.x.
46 (In particular, this happens when having expressions that contain
47 aggregate functions _and_ non-aggregates.) In this case, we go in and
48 modify the item in-place, so that the appropriate sub-expressions are
49 replaced; in this case, to (<temporary>.x + 1). This assumes that we
50 never use the same item before and after a materialization in the
51 query plan!
52 4. The item is not in items_to_copy but it is an aggregate item, so it
53 *has* to have a replacement created. In such case, 'agg_items_to_copy' is
54 non-null, and it indicates that a new items_to_copy list is to be saved
55 into this. It is made up of all such aggregate items that were not found
56 while finding replacement. These items need to be added in
57 'agg_items_to_copy' so that further items get a direct match for
58 subsequent occurences of these items, rather than generating a new
59 replacement. Without this, the replacement does not propagate from the
60 bottom to the top plan node.
62 */
64 THD *thd, Item *item, const Func_ptr_array &items_to_copy,
65 bool need_exact_match, Func_ptr_array *agg_items_to_copy = nullptr);
68 Like FindReplacementOrReplaceMaterializedItems, but only search _below_ the
69 item, ie. ignore point 2 above. This can be useful if doing self-replacement,
70 ie., we are replacing source items in items_to_copy and don't want to
71 replace an item with its own output.
72 */
73void ReplaceMaterializedItems(THD *thd, Item *item,
74 const Func_ptr_array &items_to_copy,
75 bool need_exact_match);
78 Replace "@var:=<expr>" with "@var:=<tmp_table_column>" rather than
79 "<tmp_table_column>".
81 If a join field such as "@var:=expr" points to a temp table field, the
82 var assignment won't happen because there is no re-evaluation of the
83 materialized field. . So, rather than returning the temp table field,
84 return a new Item_func_set_user_var item that points to temp table
85 field, so that "@var" gets updated.
87 (It's another thing that the temp table field itself is an
88 Item_func_set_user_var field, i.e. of the form "@var:=<expr>", which
89 means the var assignment redundantly happens for *each* temp table
90 record while initializing the table; but this function does not fix
91 that)
93 TODO: remove this function cf. deprecated setting of variable in
94 expressions when it is finally disallowed.
95 */
96Item *ReplaceSetVarItem(THD *thd, Item *item, Item *new_item);
Helper class for copy_funcs(); represents an Item to copy from table to next tmp table.
Definition: temp_table_param.h:48
Definition: item.h:4370
Base class that is used to represent any kind of expression in a relational query.
Definition: item.h:930
A typesafe replacement for DYNAMIC_ARRAY.
Definition: mem_root_array.h:426
For each client connection we create a separate thread with THD serving as a thread/connection descri...
Definition: sql_lexer_thd.h:36
Item * ReplaceSetVarItem(THD *thd, Item *item, Item *new_item)
Replace "@var:=<expr>" with "@var:=<tmp_table_column>" rather than "<tmp_table_column>".
void ReplaceMaterializedItems(THD *thd, Item *item, const Func_ptr_array &items_to_copy, bool need_exact_match)
Like FindReplacementOrReplaceMaterializedItems, but only search below the item, ie.
Item * FindReplacementOrReplaceMaterializedItems(THD *thd, Item *item, const Func_ptr_array &items_to_copy, bool need_exact_match, Func_ptr_array *agg_items_to_copy=nullptr)