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As a part of preparatory work for MDEV-4912, we'll add a new virtual method in Type_handler:
virtual Item_cache *Item_get_cache(THD *thd, const Item *item) const;
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and split this code into implementations of the new virtual method:
Item_cache* Item_cache::get_cache(THD *thd, const Item *item,
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const Item_result type)
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{
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MEM_ROOT *mem_root= thd->mem_root;
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switch (type) {
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case INT_RESULT:
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return new (mem_root) Item_cache_int(thd, item->field_type());
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case REAL_RESULT:
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return new (mem_root) Item_cache_real(thd);
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case DECIMAL_RESULT:
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return new (mem_root) Item_cache_decimal(thd);
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case STRING_RESULT:
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return new (mem_root) Item_cache_str(thd, item);
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case ROW_RESULT:
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return new (mem_root) Item_cache_row(thd);
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case TIME_RESULT:
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return new (mem_root) Item_cache_temporal(thd, item->field_type());
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}
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return 0; // Impossible
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}
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This will allow data type plugins to create their own versions of Item_cache, to optimize comparison with constants.
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