char使用固定長度的空間進行存儲，char(4)存儲4個字符，根據編碼方式的不同占用不同的字節(jié)，gbk編碼方式，不論是中文還是英文，每個字符占用2個字節(jié)的空間，utf8編碼方式，每個字符占用3個字節(jié)的空間。
如果需要存儲的字符串的長度跟所有值的平均長度相差不大，適合用char，如MD5。
對于經常改變的值，char優(yōu)于varchar，原因是固定長度的行不容易產生碎片。
對于很短的列，char優(yōu)于varchar，原因是varchar需要額外一個或兩個字節(jié)存儲字符串的長度。

varchar保存可變長度的字符串，使用額外的一個或兩個字節(jié)存儲字符串長度，varchar(10),除了需要存儲10個字符，還需要1個字節(jié)存儲長度信息(10),超過255的長度需要2個字節(jié)來存儲
例外：Myisam引擎中使用ROW_FORMAT=FIXED時，每行使用相同的空間，造成浪費

char和varchar后面如果有空格，char會自動去掉空格后存儲，varchar雖然不會去掉空格，但在進行字符串比較時，會去掉空格進行比較

+-------+--------------+------+-----+---------+----------------+
| Field | Type?????????| Null | Key | Default | Extra??????????|
+-------+--------------+------+-----+---------+----------------+
| id????| int(11)??????| NO???| PRI | NULL????| auto_increment |
| name??| varchar(4)???| YES??|?????| NULL????|????????????????|
| addr??| char(8)??????| YES??|?????| NULL????|????????????????|
| bn????| varbinary(4) | YES??|?????| NULL????|????????????????|
| b?????| binary(8)????| YES??|?????| NULL????|????????????????|
+-------+--------------+------+-----+---------+----------------+
+----------------------+----------------------+
| concat("$",name,"$") | concat("$",addr,"$") |
+----------------------+----------------------+
| $asdf$???????????????| $a$??????????????????|
| $asdf$???????????????| $a$??????????????????|
| $a $?????????????????| $a$??????????????????|
| $a$??????????????????| $a$??????????????????|
| $t a$????????????????| $a$??????????????????|
+----------------------+----------------------+
mysql> select * from zcy where name='a ';???//由于name是varchar，比較時，'a '自動轉換為'a'

+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??3 | a????| a????| ab???| ab???????|
|??4 | a????| a????| ab???| a????????|
+----+------+------+------+----------+
2 rows in set (0.00 sec)

mysql> select * from zcy where name='a';
+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??3 | a????| a????| ab???| ab???????|
|??4 | a????| a????| ab???| a????????|
+----+------+------+------+----------+
2 rows in set (0.00 sec)


+-------+--------------+------+-----+---------+----------------+
| Field | Type?????????| Null | Key | Default | Extra??????????|
+-------+--------------+------+-----+---------+----------------+
| id????| int(11)??????| NO???| PRI | NULL????| auto_increment |
| name??| varchar(4)???| YES??|?????| NULL????|????????????????|
| addr??| char(8)??????| YES??|?????| NULL????|????????????????|
| bn????| varbinary(4) | YES??|?????| NULL????|????????????????|
| b?????| binary(8)????| YES??|?????| NULL????|????????????????|
+-------+--------------+------+-----+---------+----------------+
+--------------------+-------------------+
| concat("$",bn,"$") | concat("$",b,"$") |
+--------------------+-------------------+
| $ab a$?????????????| NULL??????????????|
| $ab $??????????????| $ab??????$????????|
| $ab$???????????????| $ab??????$????????|
| $ab??$?????????????| $a???????$????????|
| NULL???????????????| $a???????$????????|
| NULL???????????????| $abcde???$????????|
| NULL???????????????| $abcd1234$????????|
+--------------------+-------------------+

binary保存二進制字符串，它保存的是字節(jié)而不是字符，沒有字符集限制
binary(8)可以保存8個字符，每個字符占1個字節(jié)，共占8個字節(jié)
進行比較時是按字節(jié)進行比較，而不是按字符（char），按字節(jié)比較比字符簡單快速
按字符比較不區(qū)分大小寫，而binary區(qū)分大小寫，結尾使用\0填充，而不是空格
mysql> select * from zcy where b='a\0\0\0\0\0\0\0';
+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??5 | t a??| a????| NULL | a????????|
+----+------+------+------+----------+
mysql> select * from zcy where b='a \0\0\0\0\0\0';?
+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??4 | a????| a????| ab???| a????????|
+----+------+------+------+----------+

varbinary保存變長的字符串，后面不會補\0
mysql> select * from zcy where bn='ab';
+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??3 | a????| a????| ab???| ab???????|
+----+------+------+------+----------+
1 row in set (0.01 sec)

mysql> select * from zcy where bn='ab ';
+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??2 | asdf | a????| ab???| ab???????|
+----+------+------+------+----------+
1 row in set (0.00 sec)

mysql> select * from zcy where bn='ab??';
+----+------+------+------+----------+
| id | name | addr | bn???| b????????|
+----+------+------+------+----------+
|??4 | a????| a????| ab???| a????????|
+----+------+------+------+----------+
1 row in set (0.00 sec)

總結

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