Data type binary string type

9.4　 Binary string type

MySQL The binary string type in mainly stores some binary data , For example, you can store pictures 、 Binary data such as audio and video , This section briefly introduces MySQL Supported binary string types .

9.4.1　 Overview of binary string types

MySQL Binary string types supported in mainly include BIT、BINARY、VARBINARY、TINYBLOB、BLOB、MEDIUMBLOB and LONGBLOB type . The length and storage space of each type are shown in the table 9-10 Shown .

surface 9-10　 Binary string type length and occupied space

The storage space occupied by each binary string type is also different .

9.4.2　BIT type

BIT Type in the , The minimum number of digits of each value is 1, The maximum value is 64, The default number of digits is 1.BIT Type stores binary values .

Create data table t20,t20 The data table contains a BIT Type field b.

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mysql> CREATE TABLE t20 (    -> b BIT(5)    -> );Query OK, 0 rows affected (0.02 sec)

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towards t20 Insert data into the table 2、8、16.

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mysql> INSERT INTO t20 (b) VALUES (2), (8), (16);Query OK, 3 rows affected (0.00 sec)Records: 3  Duplicates: 0  Warnings: 0

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see t20 Table data .

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mysql> SELECT * FROM t20;+------+| b    |+------+|      ||      ||      |+------+3 rows in set (0.00 sec)

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Use SELECT*FROM t20 The data queried by the statement cannot be viewed , This is because BIT Type stores binary data .

Use the following statement to query t20 Table data .

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mysql> SELECT BIN(b+0) FROM t20;+----------+| BIN(b+0) |+----------+| 10       || 1000     || 10000    |+----------+3 rows in set (0.00 sec)

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It can be seen that , It has been found correctly 2、8、16 The binary value of . among , In the query statement b+0（b Represents the defined field name b） It means that the result of the stored binary value is converted into the value of the corresponding binary digit .BIN() Function converts a number to binary .

You can also use the following statement to query t20 Data stored in tables .

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mysql> SELECT b+0 FROM t20;     +------+| b+0  |+------+|    2 ||    8 ||   16 |+------+3 rows in set (0.00 sec)

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You can see , Use b+0 When querying data , The decimal value can be directly queried .

Be careful ： In the BIT When inserting data into a field of type , Be sure to insert data in BIT Within the scope of type support .

9.4.3　BINARY And VARBINARY type

BINARY The type is a fixed length binary type , When the inserted data does not reach the specified length , Will be filled after the data “\0” character , To reach the specified length . meanwhile BINARY The storage space of the type field is also a fixed value .

VARBINARY The type is variable length binary type , The minimum length is 0, The maximum value is defined VARBINARY The length value specified when a field of type , Its storage space is the actual length of the data plus 1.

Create data table t21,t21 There is one in the table BINARY Type field b And one VARBINARY Type field vb.

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mysql> CREATE TABLE t21 (    -> b BINARY(10),    -> vb VARBINARY(10)    -> );Query OK, 0 rows affected (0.02 sec)

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among ,b Fields and vb The length specified in the field is 10.

towards t21 Insert data into the table .

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mysql> INSERT INTO t21 (b ,vb) VALUES (10, 10);Query OK, 1 row affected (0.01 sec)

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Inquire about t21 The length of the data in the table .

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mysql> SELECT LENGTH(b), LENGTH(vb) FROM t21;+-----------+------------+| LENGTH(b) | LENGTH(vb) |+-----------+------------+|        10 |         2  |+-----------+------------+1 row in set (0.00 sec)

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You can see ,b The length of the field data is 10,vb The data length of the field is 2. explain BINARY The field length of type is a fixed value , The length of the field specified when defining the field , and VARBINARY The value of the field length of type is variable .

9.4.4　BLOB type

MySQL Medium BLOB Types include TINYBLOB、BLOB、MEDIUMBLOB and LONGBLOB 4 Types , Can store a large binary object , Such as the picture 、 Audio and video, etc .

It should be noted that , In practice , Often not in MySQL Use in the database BLOB Type stores large object data , Usually the picture 、 Audio and video files are stored on the disk of the server , And put the picture 、 The access paths of audio and video are stored in MySQL in .