InnoDB一定会在索引中加上主键吗

CREATETABLE t (
  a char(32)notnullprimarykey,
  b char(32)notnull,KEY idx1 (a,b),KEY idx2 (b,a)) Engine=      InnoDB;

2727/*******************************************************************//**2728 Builds the internal dictionary cache representation for a non-clustered2729 index, containing also system fields not defined by the user.2730 @return own: the internal representation of the non-clustered index */2731static2732 dict_index_t*2733 dict_index_build_internal_non_clust(2734/*================================*/2735const dict_table_t* table,  /*!< in: table */2736   dict_index_t*   index)/*!< in: user representation of2737           a non-clustered index */2738{2739   dict_field_t* field;2740   dict_index_t* new_index;2741   dict_index_t* clust_index;2742   ulint   i;2743   ibool*    indexed;27442745   ut_ad(table && index);2746   ut_ad(!dict_index_is_clust(index));2747   ut_ad(mutex_own(&(dict_sys->mutex)));2748   ut_ad(table->magic_n == DICT_TABLE_MAGIC_N);27492750/* The clustered index should be the first in the list of indexes */2751   clust_index = UT_LIST_GET_FIRST(table->indexes);27522753   ut_ad(clust_index);2754   ut_ad(dict_index_is_clust(clust_index));2755   ut_ad(!dict_index_is_univ(clust_index));27562757/* Create a new index */2758   new_index = dict_mem_index_create(2759     table->name, index->name, index->space, index->type,
2760     index->n_fields +1+ clust_index->n_uniq);27612762/* Copy other relevant data from the old index2763   struct to the new struct: it inherits the values */27642765   new_index->n_user_defined_cols = index->n_fields;27662767   new_index->id = index->id;27682769/* Copy fields from index to new_index */2770   dict_index_copy(new_index, index, table, 0, index->n_fields);27712772/* Remember the table columns already contained in new_index */2773   indexed =static_cast<ibool*>(2774     mem_zalloc(table->n_cols *sizeof*indexed));27752776/* Mark the table columns already contained in new_index */2777for(i =0; i < new_index->n_def; i++){27782779     field = dict_index_get_nth_field(new_index, i);27802781/* If there is only a prefix of the column in the index2782     field, do not mark the column as contained in the index */27832784if(field->prefix_len ==0){27852786       indexed[field->col->ind]= TRUE;2787}2788}27892790/* Add to new_index the columns necessary to determine the clustered2791   index entry uniquely */27922793for(i =0; i < clust_index->n_uniq; i++){27942795     field = dict_index_get_nth_field(clust_index, i);27962797if(!indexed[field->col->ind]){2798       dict_index_add_col(new_index, table, field->col,
2799              field->prefix_len);2800}2801}28022803   mem_free(indexed);28042805if(dict_index_is_unique(index)){2806     new_index->n_uniq = index->n_fields;2807}else{2808     new_index->n_uniq = new_index->n_def;2809}28102811/* Set the n_fields value in new_index to the actual defined2812   number of fields */28132814   new_index->n_fields = new_index->n_def;28152816   new_index->cached = TRUE;28172818return(new_index);2819}

474unsigned  n_user_defined_cols:10;475/*!< number of columns the user defined to 476         be in the index: in the internal 477         representation we add more columns */478unsigned  n_uniq:10;/*!< number of fields from the beginning                                                                                                                                                                          479         which are enough to determine an index 480         entry uniquely */481unsigned  n_def:10;/*!< number of fields defined so far */482unsigned  n_fields:10;/*!< number of fields in the index */

2772/* Remember the table columns already contained in new_index */2773   indexed =static_cast<ibool*>(2774     mem_zalloc(table->n_cols *sizeof*indexed));27752776/* Mark the table columns already contained in new_index */2777for(i =0; i < new_index->n_def; i++){27782779     field = dict_index_get_nth_field(new_index, i);27802781/* If there is only a prefix of the column in the index2782     field, do not mark the column as contained in the index */27832784if(field->prefix_len ==0){27852786       indexed[field->col->ind]= TRUE;2787}2788}

2790/* Add to new_index the columns necessary to determine the clustered2791   index entry uniquely */27922793for(i =0; i < clust_index->n_uniq; i++){27942795     field = dict_index_get_nth_field(clust_index, i);27962797if(!indexed[field->col->ind]){2798       dict_index_add_col(new_index, table, field->col,
2799              field->prefix_len);2800}2801}

CREATETABLE t (
  a char(32)notnull,
  b char(32)notnull,
  c char(32)notnull,
  d char(32)notnull,PRIMARYKEY(a,b)KEY idx1 (c,a),KEY idx2 (d,b)) Engine=InnoDB;

SELECT * FROM t WHERE d=x1 AND b=x2 ORDER BY a;