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This article introduces the relevant knowledge of "what are the shortcomings of the MySQL memory table". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

CREATETABLE`mem _ test` (`id`int (10) unsignedNOTNULLDEFAULT'0', `name`varchar (10) DEFAULTNULL, `first`varchar (10) DEFAULTNULL,PRIMARYKEY (`id`), KEY`NewIndex1` (`name`, `first`)) ENGINE=MEMORY; CREATETABLE`innodb _ test` (`id`int (10) unsignedNOTNULLDEFAULT'0', `name`varchar (10) DEFAULTNULL, `first`varchar (10) DEFAULTNULL,PRIMARYKEY (`id`), KEY`NewIndex1` (`name`, `first`))

Such as:

1: in the = or case, very fast, but in this case, he does not use the index

Mysql--chinastor.com-root@localhost:17db07:33:45 > > explainselect*frommem_testwhereid > 3 +-+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | + -- + | 1 | SIMPLE | mem_test | ALL | PRIMARY | NULL | 15 | Usingwhere | + -+ 1rowinset (0.00sec) mysql--chinastor.com-root@localhost:17db07:33:49 > > explainselect*frominnodb_testwhereid > 3 +-+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | + -+ | 1 | SIMPLE | innodb_test | range | PRIMARY | PRIMARY | 4 | NULL | 7 | Usingwhere | +-+-- +-+ 1rowinset (0.00sec)

2: cannot be used to increase speed in the case of orderby

Mysql--chinastor.com-root@localhost:17db07:33:55 > > explainselect*frominnodb_testorderbyid +-+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | + -+ | 1 | SIMPLE | innodb_test | index | NULL | PRIMARY | 4 | NULL | 15 | +-+ -+ 1rowinset (0.00sec) mysql--chinastor.com-root@localhost:17db07:34:27 > > explainselect*frommem_testorderbyid +-+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | + -+ | 1 | SIMPLE | mem_test | ALL | NULL | 15 | Usingfilesort | + +-+ 1rowinset (0.00sec)

What are the disadvantages of MySQL memory table

3: not sure how many rows there are between the two values

Mysql--chinastor.com-root@localhost:17db07:37:14 > > explainselectcount (1) frommem_testwhereid > 3andid > explainselectcount (1) frominnodb_testwhereid > 3andid > explainselect*frominnodb_testwherename='b' +- + | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +-- +-- + | 1 | SIMPLE | innodb_test | ref | NewIndex1 | NewIndex1 | 33 | const | 8 | Usingwhere Usingindex | +- + 1rowinset (0.00sec) mysql--chinastor.com-root@localhost:17db07:37:10 > > explainselect*frommem_testwherename='b' +-+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | + -- + | 1 | SIMPLE | mem_test | ALL | NewIndex1 | NULL | 20 | Usingwhere | + -+

Of course, you can also add btree manually to the memory table.

CREATEINDEXBTREE_indexUSINGBTREEonmem_test (name,first) mysql--chinastor.com-root@localhost:17db03:36:41 > > explainselect*frommem_testwherename='b' +-+-- +-+ | id | select_type | table | type | possible_keys | key | key_ Len | ref | rows | Extra | +-+-+ | 1 | SIMPLE | mem_test | ref | NewIndex1 BTREE_index | BTREE_index | 33 | const | 9 | Usingwhere | +-+-- + 1rowinset (0.00sec)

Haha, it also uses the index.

Therefore, it is very important to choose the right storage engine.

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