msyql set names 字符转换处理

sql_insert.cc::fill_record_n_invoke_before_triggers
sql_base.cc::fill_record
item.cc::save_in_field
item.cc::save_in_field_inner
item.cc::save_str_value_in_field
field.cc Field_string::store
field.cc field_well_formed_copy_nchars

size_t well_formed_copy_nchars(const CHARSET_INFO *to_cs, char *to,
                               size_t to_length, const CHARSET_INFO *from_cs,
                               const char *from, size_t from_length,
                               size_t nchars,
                               const char **well_formed_error_pos,
                               const char **cannot_convert_error_pos,
                               const char **from_end_pos) {

如果字符相同不做转换
如果字符不同
my_charset_conv_mb_wc mb_wc = from_cs->cset->mb_wc;
my_charset_conv_wc_mb wc_mb = to_cs->cset->wc_mb;

根据query的字符和char 转换 成目标的 字符集