What are the disadvantages of MySQL memory table
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.
This is the end of the content of "what are the shortcomings of the MySQL memory table". Thank you for your reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!
