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This patch implements engine independent unique hash index.
Usage:- Unique HASH index can be created automatically for blob/varchar/test column whose key
length > handler->max_key_length()
or it can be explicitly specified.
Automatic Creation:-
Create TABLE t1 (a blob unique);
Explicit Creation:-
Create TABLE t1 (a int , unique(a) using HASH);
Internal KEY_PART Representations:-
Long unique key_info will have 2 representations.
(lets understand this with an example create table t1(a blob, b blob , unique(a, b)); )
1. User Given Representation:- key_info->key_part array will be similar to what user has defined.
So in case of example it will have 2 key_parts (a, b)
2. Storage Engine Representation:- In this case there will be only one key_part and it will point to
HASH_FIELD. This key_part will be always after user defined key_parts.
So:- User Given Representation [a] [b] [hash_key_part]
key_info->key_part ----^
Storage Engine Representation [a] [b] [hash_key_part]
key_info->key_part ------------^
Table->s->key_info will have User Given Representation, While table->key_info will have Storage Engine
Representation.Representation can be changed into each other by calling re/setup_keyinfo_hash function.
Working:-
1. So when user specifies HASH_INDEX or key_length is > handler->max_key_length(), In mysql_prepare_create_table
One extra vfield is added (for each long unique key). And key_info->algorithm is set to HA_KEY_ALG_LONG_HASH.
2. In init_from_binary_frm_image values for hash_keypart is set (like fieldnr , field and flags)
3. In parse_vcol_defs, HASH_FIELD->vcol_info is created. Item_func_hash is used with list of Item_fields,
When Explicit length is given by user then Item_left is used to concatenate Item_field values.
4. In ha_write_row/ha_update_row check_duplicate_long_entry_key is called which will create the hash key from
table->record[0] and then call ha_index_read_map , if we found duplicated hash , we will compare the result
field by field.
54 lines
1.5 KiB
Text
54 lines
1.5 KiB
Text
create table t1(a blob , unique(a) using hash);
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show keys from t1;;
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Table t1
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Non_unique 0
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Key_name a
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Seq_in_index 1
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Column_name a
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Collation A
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Cardinality NULL
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Sub_part NULL
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Packed NULL
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Null YES
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Index_type HASH
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Comment
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Index_comment
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drop table t1;
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create table t1(a blob , unique(a) using btree);
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ERROR 42000: Specified key was too long; max key length is 1000 bytes
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create table t1(a int , unique(a) using hash);
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show keys from t1;;
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Table t1
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Non_unique 0
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Key_name a
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Seq_in_index 1
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Column_name a
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Collation A
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Cardinality NULL
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Sub_part NULL
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Packed NULL
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Null YES
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Index_type HASH
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Comment
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Index_comment
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drop table t1;
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create table t1(a int ,b int , c int, unique(a, b, c) using hash);
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show keys from t1;
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Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment
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t1 0 a 1 a A NULL NULL NULL YES HASH
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t1 0 a 2 b A NULL NULL NULL YES HASH
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t1 0 a 3 c A NULL NULL NULL YES HASH
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insert into t1 values(1,1,1);
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insert into t1 values(1,1,1);
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ERROR 23000: Duplicate entry '1-1-1' for key 'a'
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drop table t1;
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create table t1(a int ,b int , c int, unique(a, b, c) using hash) engine=memory;
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show keys from t1;
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Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment
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t1 0 a 1 a NULL NULL NULL NULL YES HASH
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t1 0 a 2 b NULL NULL NULL NULL YES HASH
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t1 0 a 3 c NULL 0 NULL NULL YES HASH
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insert into t1 values(1,1,1);
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insert into t1 values(1,1,1);
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ERROR 23000: Duplicate entry '1-1-1' for key 'a'
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drop table t1;
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