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MDEV-11672 mysql_list_field() returns wrong default values for VIEW
The problem happened because Item_ident_for_show::field_type() always returned MYSQL_TYPE_DOUBLE and ignored the actual data type of the referenced Field. As a result, the execution always used Item_ident_for_show::val_real() to send the default value of the field, so most default values for non-numeric types were displayed as '0'. This patch: 1. Cleanup: a. Removes Send_field::charsetnr, as it's been unused since introduction of Item::charset_for_protocol() in MySQL-5.5. b. Adds the "const" qualifier to Field::char_length(). This is needed for (5.a), see below. 2. Introduces a new virtual method Type_handler::charset_for_protocol(), returning item->collation.collation for string data types, or &my_charset_bin for non-string data types. 3. Changes Item::charset_for_protocol() from virtual to non-virtual. It now calls type_handler()->charset_for_protocol(). As a good side effect, duplicate code in Item::charset_for_protocol() and Item_temporal_hybrid_func::charset_for_protocol() is now gone. 4. Fixes Item_ident_for_show::field_type() to correctly return its data type according to the data type of the referenced field. This actually fixes the problem reported in MDEV-11672. Now the default value is sent using a correct method, e.g. val_str() for VARCHAR/TEXT, or val_int() for INT/BIGINT. This required additional changes: a. in DBUG_ASSERT in Protocol::store(const char *,size_t,CHARSET_INFO), This method is now used by mysqld_list_fields(), which (unlike normal SELECT queries) does not set field_types/field_pos/field_count. b. Item_ident_for_show::Item_ident_for_show() now set standard attributes (collation, decimals, max_length, unsigned_flag) according to the referenced field, to make charset_for_protocol() return the correct value and to make mysqld_list_fields() correctly send default values. 5. In order to share the code between Item_field::set_field() and Item_ident_for_show::Item_ident_for_show(): a. Introduces a new method Type_std_attributes::set(const Field*) b. To make (a) possible, moves Item::fix_char_length() from Item to Type_std_attributes, also moves char_to_byte_length_safe() from item.h to sql_type.h c. Additionally, moves Item::fix_length_and_charset() and Item::max_char_length() from Item to Type_std_attributes. This is not directly needed for the fix and is done just for symmetry with fix_char_length(), as these three methods are directly related to each other.
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Alexander Barkov
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Dec 29, 2016
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