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  • KEYUSE

    typedef struct keyuse_t {
      TABLE *table;
      Item    *val;                /**< or value if no field */
      table_map used_tables;
      uint    key, keypart, optimize;
      key_part_map keypart_map;
      ha_rows      ref_table_rows;
      /**
        If true, the comparison this value was created from will not be
        satisfied if val has NULL 'value'.
      */
      bool null_rejecting;
      /*
        !NULL - This KEYUSE was created from an equality that was wrapped into
                an Item_func_trig_cond. This means the equality (and validity of 
                this KEYUSE element) can be turned on and off. The on/off state 
                is indicted by the pointed value:
                  *cond_guard == TRUE <=> equality condition is on
                  *cond_guard == FALSE <=> equality condition is off
    
        NULL  - Otherwise (the source equality can't be turned off)
      */
      bool *cond_guard;
    } KEYUSE;
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  • 原文地址:https://www.cnblogs.com/taek/p/5217039.html
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