Digital currency bdb
Publish: 2021-04-18 20:25:41
1. China has relevant legislation on e-commerce, but it is not perfect.
2. 1、 Data type
MySQL supports all standard SQL numeric data types
these types include strict numeric data types (integer, smartint, decimal and numeric), and approximate numeric data types (float, real and double precision)
the keyword int is synonymous with integer, and the keyword Dec is synonymous with decimal
the integer types supported by MySQL are tinyint, mediumint and bigint. The following table shows the storage and range of each integer type required
for decimal representation, MySQL can be divided into two ways: floating point number and fixed point number. Floating point numbers include float (single precision) and double (double precision), while fixed point numbers are only decimal. They are stored in the form of strings in mysql, which are more accurate than floating-point numbers and are suitable for representing data with high precision such as currency
bit data type saves bit field values and supports MyISAM, memory, InnoDB and BDB tables
type size range (signed) range (unsigned) constraint usage tinyint1 byte (- 128127) (0255) small integer value smallint2 byte (- 32768, 32767) (0, 65535) large integer value mediumint3 byte (- 8388608, 8388607) (0, 16777215) large integer value int or integer4 byte (- 2 147483 648, 2 147483 647) (0, 4 294 967 295) big integer value bigint8 bytes (- 9 233 372 036 854 775 808, 9 223 372 036 854 775 807) (0, 18 446 744 073 709 551 615) big integer value float4 bytes
float (255,30) (- 3.402 823 466 e + 38, - 1.175 494 351 e-38), 0, (1.175 494 351 e-38, 3.402 823 466 351 e + 38) 0, (1.175 494 351 e-38, 3.402 823 466 e + 38) single precision
double 8 bytes of floating-point value
double (255,30) (- 1.797 693 134 862 315 7 e + 308, - 2.225 073 858 507 201 4 e-308), 0, (2.225 073 858 507 201 4 e-308, 1.797 693 134 862 315 7 e + 308) 0, (2.225 073 858 507 201 4 e-308, 1.797 693 134 862 315 7 e + 308) double precision
floating-point value DEM vs. decimal, D) , if M & gt; D. For M + 2 or D + 2
double (65,30) values depending on M and D, values depending on M and D, decimal value 1.1 int integer example
# create a table with an int of default width and an int (5) of specified width
MySQL & gt; create table t1 (id1 int,id2 int(5));
query OK, 0 rows affected (0.02 sec)
insert data 1, 1
MySQL & gt; insert into t1 values (1,1);
query OK, 1 row affected (0.01 sec)
? We can see that there is no exception in the result
MySQL & gt; select * from t1;
+ - + - - - +
| Id1 | Id2 |
+ - + - - - +
| 1 | 1 |
+ - + - - +
row in set (0.00 sec)
# so when we insert a value larger than the width, will the error be reported< br />
mysql> insert into t1 values (111111,111111);
query OK, 1 row affected (0.00 sec)
? The answer is no, Id2 still shows the correct value, not affected by the width limit
MySQL & gt; select * from t1;< br />
+------------+--------+
| id1 | id2 |
+------------+--------+
| 0000000001 | 00001 |
| 0000111111 | 111111 |
+------------+--------+
rows in set (0.00 sec)
MySQL supports all standard SQL numeric data types
these types include strict numeric data types (integer, smartint, decimal and numeric), and approximate numeric data types (float, real and double precision)
the keyword int is synonymous with integer, and the keyword Dec is synonymous with decimal
the integer types supported by MySQL are tinyint, mediumint and bigint. The following table shows the storage and range of each integer type required
for decimal representation, MySQL can be divided into two ways: floating point number and fixed point number. Floating point numbers include float (single precision) and double (double precision), while fixed point numbers are only decimal. They are stored in the form of strings in mysql, which are more accurate than floating-point numbers and are suitable for representing data with high precision such as currency
bit data type saves bit field values and supports MyISAM, memory, InnoDB and BDB tables
type size range (signed) range (unsigned) constraint usage tinyint1 byte (- 128127) (0255) small integer value smallint2 byte (- 32768, 32767) (0, 65535) large integer value mediumint3 byte (- 8388608, 8388607) (0, 16777215) large integer value int or integer4 byte (- 2 147483 648, 2 147483 647) (0, 4 294 967 295) big integer value bigint8 bytes (- 9 233 372 036 854 775 808, 9 223 372 036 854 775 807) (0, 18 446 744 073 709 551 615) big integer value float4 bytes
float (255,30) (- 3.402 823 466 e + 38, - 1.175 494 351 e-38), 0, (1.175 494 351 e-38, 3.402 823 466 351 e + 38) 0, (1.175 494 351 e-38, 3.402 823 466 e + 38) single precision
double 8 bytes of floating-point value
double (255,30) (- 1.797 693 134 862 315 7 e + 308, - 2.225 073 858 507 201 4 e-308), 0, (2.225 073 858 507 201 4 e-308, 1.797 693 134 862 315 7 e + 308) 0, (2.225 073 858 507 201 4 e-308, 1.797 693 134 862 315 7 e + 308) double precision
floating-point value DEM vs. decimal, D) , if M & gt; D. For M + 2 or D + 2
double (65,30) values depending on M and D, values depending on M and D, decimal value 1.1 int integer example
# create a table with an int of default width and an int (5) of specified width
MySQL & gt; create table t1 (id1 int,id2 int(5));
query OK, 0 rows affected (0.02 sec)
insert data 1, 1
MySQL & gt; insert into t1 values (1,1);
query OK, 1 row affected (0.01 sec)
? We can see that there is no exception in the result
MySQL & gt; select * from t1;
+ - + - - - +
| Id1 | Id2 |
+ - + - - - +
| 1 | 1 |
+ - + - - +
row in set (0.00 sec)
# so when we insert a value larger than the width, will the error be reported< br />
mysql> insert into t1 values (111111,111111);
query OK, 1 row affected (0.00 sec)
? The answer is no, Id2 still shows the correct value, not affected by the width limit
MySQL & gt; select * from t1;< br />
+------------+--------+
| id1 | id2 |
+------------+--------+
| 0000000001 | 00001 |
| 0000111111 | 111111 |
+------------+--------+
rows in set (0.00 sec)
3. 1[UNK]B_;2[UNK]D_;3[UNK]C_;4[UNK]B_;5[UNK]A_;6[UNK]D_[UNK]A_;8[UNK]A_;9[UNK]D_;10[UNK]B
4. On January 28, ElBaradei, the leader of Egyptian reformists, returned home to demonstrate
on January 29, in the 2011 Australian Open women's singles final, Li Na was defeated by Clijsters and ranked second
on February 3, the tallest building in Northeast China caught fire
on February 4, the EU summit opened in Brussels
on February 5, there was a fight between Hong Kong tour guides and mainland tourists< On February 6, the 7th Asian Winter Games came to an end in Kazakhstan. China's sports delegation won 11 gold medals, 10 silver medals and 14 bronze medals, ranking fourth in the medal list. This is the worst place for the Chinese delegation in the 25 year history of participating in the Asian Winter Games
on February 7, Thailand and Cambodia exchanged fire in the border area
on February 9, the central bank raised interest rates by 0.25 percentage points
on February 10, Egyptian President Mubarak partially handed over power to Vice President Suleiman< On February 11, Egyptian President Mubarak announced his resignation< According to xinhuanet.com, Liu Zhijun, Secretary of the Party group and Minister of the Ministry of railways, is suspected of serious violations of discipline and is currently under investigation. The Central Committee has been removed from the post of secretary of the Party group, and Sheng Guangzu has been appointed to take over the post of secretary of the Party group of the Ministry of railways
recently, there has been no effective precipitation for more than 140 days in most parts of Shandong Province, and the ration has reached the historical extreme. If there is no large-scale effective precipitation by the end of March, the meteorological drought level of the whole province will reach once in a thousand years.
on January 29, in the 2011 Australian Open women's singles final, Li Na was defeated by Clijsters and ranked second
on February 3, the tallest building in Northeast China caught fire
on February 4, the EU summit opened in Brussels
on February 5, there was a fight between Hong Kong tour guides and mainland tourists< On February 6, the 7th Asian Winter Games came to an end in Kazakhstan. China's sports delegation won 11 gold medals, 10 silver medals and 14 bronze medals, ranking fourth in the medal list. This is the worst place for the Chinese delegation in the 25 year history of participating in the Asian Winter Games
on February 7, Thailand and Cambodia exchanged fire in the border area
on February 9, the central bank raised interest rates by 0.25 percentage points
on February 10, Egyptian President Mubarak partially handed over power to Vice President Suleiman< On February 11, Egyptian President Mubarak announced his resignation< According to xinhuanet.com, Liu Zhijun, Secretary of the Party group and Minister of the Ministry of railways, is suspected of serious violations of discipline and is currently under investigation. The Central Committee has been removed from the post of secretary of the Party group, and Sheng Guangzu has been appointed to take over the post of secretary of the Party group of the Ministry of railways
recently, there has been no effective precipitation for more than 140 days in most parts of Shandong Province, and the ration has reached the historical extreme. If there is no large-scale effective precipitation by the end of March, the meteorological drought level of the whole province will reach once in a thousand years.
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