MySQL bit type resolution

BIT Type introduction

BIT Data types are used to store bit values . Its data has two values ：0 and 1, This data type is often used as a logical variable , Used to express true 、 False or yes 、 No, wait for binary selection . More like the most primitive computer language programming .

stay MySQL in BIT Summarized as Numeric Data type .BIT The data type stores bit values , Support MyISAM、MEMORY、InnoDB、NDB surface .

In data types ,bit It should occupy the smallest space .

BIT(M) Type allows storage M A value .M The value range is 1 ~ 64.NDB All in the cluster BIT The maximum sum of columns cannot exceed 4096 position

If you assign a value with a length less than M Bit BIT(M) Column , Then the value will be filled in on the left 0.
for example : to BIT(6) Column assignment b’101’ In fact, it is equivalent to giving b’000101’ assignment .

that BIT What environment is suitable for the scene , In the real world , A typical case , attendance .“1” Show attendance ,“0” Indicate absence , This makes it easier to identify the days when everyone is present or absent .

MySQL> DROP TABLE IF EXISTS attendance;
MySQL> CREATE TABLE attendance (
emp_no  CHAR(3),
emp_name CHAR(50),
attend BIT(5),
class  INT,
KEY `idx_bit` (`attend`)
);

# Use b'val' The way of writing , Val It's using 0 and 1 Written binary values 
MySQL> INSERT INTO attendance (emp_no, emp_name, attend, class)
VALUES ('001','Jim',b'11111',5),('002','Kim',b'11000',5),('003','Cui',b'00111',5),
('004','King',b'11101',5),('005','Wang',b'101',5),('006','Chen',NULL,5),
('007','Piao',0,5),('008','Hu',1,5);

MySQL> SELECT  emp_no,emp_name,attend ,class  FROM  attendance;
+--------+----------+----------------+-------+
| emp_no | emp_name | attend         | class |
+--------+----------+----------------+-------+
| 001    | Jim      | 0x1F           |     5 |
| 002    | Kim      | 0x18           |     5 |
| 003    | Cui      | 0x07           |     5 |
| 004    | King     | 0x1D           |     5 |
| 005    | Wang     | 0x05           |     5 |
| 006    | Chen     | NULL           |     5 |
| 007    | Piao     | 0x00           |     5 |
| 008    | Hu       | 0x01           |     5 |
+--------+----------+----------------+-------+
8 rows in set (0.00 sec)


#BIN Way to show 
MySQL> SELECT  emp_no,emp_name,BIN(attend) ,class  FROM  attendance;
+--------+----------+-------------+-------+
| emp_no | emp_name | BIN(attend) | class |
+--------+----------+-------------+-------+
| 001    | Jim      | 11111       |     5 |
| 002    | Kim      | 11000       |     5 |
| 003    | Cui      | 111         |     5 |
| 004    | King     | 11101       |     5 |
| 005    | Wang     | 101         |     5 |
| 006    | Chen     | NULL        |     5 |
| 007    | Piao     | 0           |     5 |
| 008    | Hu       | 1           |     5 |
+--------+----------+-------------+-------+
8 rows in set (0.00 sec)


# String left padding function LPAD
MySQL> SELECT  emp_no,emp_name,LPAD(BIN(attend),5,0) ,class  FROM  attendance;
+--------+----------+-----------------------+-------+
| emp_no | emp_name | LPAD(BIN(attend),5,0) | class |
+--------+----------+-----------------------+-------+
| 001    | Jim      | 11111                 |     5 |
| 002    | Kim      | 11000                 |     5 |
| 003    | Cui      | 00111                 |     5 |
| 004    | King     | 11101                 |     5 |
| 005    | Wang     | 00101                 |     5 |
| 006    | Chen     | NULL                  |     5 |
| 007    | Piao     | 00000                 |     5 |
| 008    | Hu       | 00001                 |     5 |
+--------+----------+-----------------------+-------+
8 rows in set (0.00 sec)

remarks ：
You can use bit valued functions , And you can use decimal 、 Binary or any other data conversion function retrieves bit values . Use LPAD and BIN Function to retrieve data in the appropriate format .

Data query ：

Corresponding WHERE Conditions bit Field must be b’val’ Or int type

##1. use INT Type number to query 
MySQL> SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class           
        FROM  attendance where attend=7;
+--------+----------+-------------+-------------+----------------+-------+
| emp_no | emp_name | BIN(attend) | HEX(attend) | attend         | class |
+--------+----------+-------------+-------------+----------------+-------+
| 003    | Cui      | 111         | 7           | 0x07           |     5 |
+--------+----------+-------------+-------------+----------------+-------+

##2. Query by location 
MySQL> SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class  
        FROM  attendance where attend=b'111';
+--------+----------+-------------+-------------+----------------+-------+
| emp_no | emp_name | BIN(attend) | HEX(attend) | attend         | class |
+--------+----------+-------------+-------------+----------------+-------+
| 003    | Cui      | 111         | 7           | 0x07           |     5 |
+--------+----------+-------------+-------------+----------------+-------+

##3.string Type to query 
MySQL> SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class           
              FROM  attendance where attend='7';
Empty set (0.00 sec)

##4.in  The statement is partially invalid （ character string ）
MySQL> SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class                  
       FROM  attendance WHERE attend in('7',5);
+--------+----------+-------------+-------------+----------------+-------+
| emp_no | emp_name | BIN(attend) | HEX(attend) | attend         | class |
+--------+----------+-------------+-------------+----------------+-------+
| 003    | Cui      | 111         | 7           | 0x07           |     5 |
+--------+----------+-------------+-------------+----------------+-------+

##5. NULL A field 
MySQL> SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class           
       FROM  attendance WHERE attend IS NULL;
+--------+----------+-------------+-------------+----------------+-------+
| emp_no | emp_name | BIN(attend) | HEX(attend) | attend         | class |
+--------+----------+-------------+-------------+----------------+-------+
| 006    | Chen     | NULL        | NULL        | NULL           |     5 |
+--------+----------+-------------+-------------+----------------+-------+
1 row in set (0.00 sec)

remarks ：bit Fields can only be integer types or bit Type can match . Within the range of numbers b’val’ Or The integer type corresponds to the equivalent .
such as , An example of an appeal 7 and b’111’ Is equivalent . about NULL value ,bit The type is still equal to null value

Indexes

Following pair bit The field exists under the index , As a condition , Whether the index can be used .
Such as equivalent query , Range queries , type （int,bin,string）

# Numeric type 
MySQL> EXPLAIN SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class  
        FROM  attendance where attend=7;
+----+-------------+------------+------------+------+---------------+---------+---------+-------+------+----------+-------+
| id | select_type | table      | partitions | type | possible_keys | key     | key_len | ref   | rows | filtered | Extra |
+----+-------------+------------+------------+------+---------------+---------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | attendance | NULL       | ref  | idx_bit       | idx_bit | 2       | const |    1 |   100.00 | NULL  |
+----+-------------+------------+------------+------+---------------+---------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

##2. Query by location 
MySQL> EXPLAIN SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class  FROM  attendance where attend=b'111';
+----+-------------+------------+------------+------+---------------+---------+---------+-------+------+----------+-------+
| id | select_type | table      | partitions | type | possible_keys | key     | key_len | ref   | rows | filtered | Extra |
+----+-------------+------------+------------+------+---------------+---------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | attendance | NULL       | ref  | idx_bit       | idx_bit | 2       | const |    1 |   100.00 | NULL  |
+----+-------------+------------+------------+------+---------------+---------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)


##3. Range 
MySQL> EXPLAIN SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class                    
       FROM  attendance WHERE attend>17;
+----+-------------+------------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
| id | select_type | table      | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+------------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | attendance | NULL       | range | idx_bit       | idx_bit | 2       | NULL |    3 |   100.00 | Using index condition |
+----+-------------+------------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

MySQL> EXPLAIN SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class  
       FROM  attendance WHERE attend>b'111';
+----+-------------+------------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
| id | select_type | table      | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+------------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | attendance | NULL       | range | idx_bit       | idx_bit | 2       | NULL |    3 |   100.00 | Using index condition |
+----+-------------+------------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.01 sec)


##5. use string The type field 
MySQL> EXPLAIN SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class           
       FROM  attendance WHERE attend='7';
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+--------------------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                          |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+--------------------------------+
|  1 | SIMPLE      | NULL  | NULL       | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | no matching row in const table |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+--------------------------------+
1 row in set, 1 warning (0.00 sec)

remarks ： Index only accepts int , b’val’ type

BIT Functions and operators

MySQL 8.0 in , Bit functions and operators allow binary string type parameters (binary, VARBINARY and BLOB type ). This makes it possible to produce more than 64 Return value of bit , Easier to perform bit operations . Bit functions and operators include BIT_COUNT()、BIT_AND()、BIT_OR()、BIT_XOR()、&、|、^、~、<< and >>.

Be careful ：MySQL 8.0 Bit operations on binary string parameters in may result in 5.7 Different results . therefore MySQL 5.7 and 8.0 There may be incompatible information between .

#BIT_COUNT(）
MySQL> SELECT  emp_no,emp_name,BIN(attend),HEX(attend),attend ,class,bit_count(attend)  FROM  attendance;
+--------+----------+-------------+-------------+----------------+-------+-------------------+
| emp_no | emp_name | BIN(attend) | HEX(attend) | attend         | class | bit_count(attend) |
+--------+----------+-------------+-------------+----------------+-------+-------------------+
| 001    | Jim      | 11111       | 1F          | 0x1F           |     5 |                 5 |
| 002    | Kim      | 11000       | 18          | 0x18           |     5 |                 2 |
| 003    | Cui      | 111         | 7           | 0x07           |     5 |                 3 |
| 004    | King     | 11101       | 1D          | 0x1D           |     5 |                 4 |
| 005    | Wang     | 101         | 5           | 0x05           |     5 |                 2 |
| 006    | Chen     | NULL        | NULL        | NULL           |     5 |              NULL |
| 007    | Piao     | 0           | 0           | 0x00           |     5 |                 0 |
| 008    | Hu       | 1           | 1           | 0x01           |     5 |                 1 |
+--------+----------+-------------+-------------+----------------+-------+-------------------+
8 rows in set (0.00 sec)

#UUID  and  IPV6 Some of the transformations , Because it contains some “-”,“：：” The symbol of 
MySQL> SELECT HEX(UUID_TO_BIN('6ccd780c-baba-1026-9564-5b8c656024db'));
+----------------------------------------------------------+
| HEX(UUID_TO_BIN('6ccd780c-baba-1026-9564-5b8c656024db')) |
+----------------------------------------------------------+
| 6CCD780CBABA102695645B8C656024DB                         |
+----------------------------------------------------------+

#IPV6
MySQL> SELECT HEX(INET6_ATON('fe80::219:d1ff:fe91:1a72'));
+---------------------------------------------+
| HEX(INET6_ATON('fe80::219:d1ff:fe91:1a72')) |
+---------------------------------------------+
| FE800000000000000219D1FFFE911A72            |
+---------------------------------------------+

summary

stay MySQL According to the current for bit The understanding of the

• Use scenarios , Attendance is similar to the scenario + BIT_COUNT Statistics .
• bit The most practical function is UUID ,IPV6 To deal with .
• Data length and storage , Generally, the minimum length ,0 and 1 Combine the underlying data structures .
• In terms of index construction, it still follows the integer type Btree.