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Better comments about KEY::ext_key_part_map

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This commit is contained in:
Sergei Petrunia 2014-09-25 22:12:18 +04:00
parent 30fab5fb51
commit 98c95ff1e2
1 changed files with 13 additions and 1 deletions
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14
sql/structs.h
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@ -93,7 +93,19 @@ typedef struct st_key {
uint usable_key_parts; /* Should normally be = user_defined_key_parts */
uint ext_key_parts; /* Number of key parts in extended key */
ulong ext_key_flags; /* Flags for extended key */
key_part_map ext_key_part_map; /* Bitmap of pk key parts in extension */
/*
Parts of primary key that are in the extension of this index.
Example: if this structure describes idx1, which is defined as
INDEX idx1 (pk2, col2)
and pk is defined as:
PRIMARY KEY (pk1, pk2)
then
pk1 is in the extension idx1, ext_key_part_map.is_set(0) == true
pk2 is explicitly present in idx1, it is not in the extension, so
ext_key_part_map.is_set(1) == false
*/
key_part_map ext_key_part_map;
uint block_size;
uint name_length;
enum ha_key_alg algorithm;