When designing a table structure in a normal development system, it is often necessary to have a field to identify the uniqueness of the record, which is implemented from different dimensions of the java level and the database level
java generates unique identity
Version 1
Unique identifier UUID generated by java
System.out.println(UUID.randomUUID().toString());
output
4880d2b4-bc5f-48d1-ba58-003334276d46
Obviously it's too long and unfriendly
Version two
Further processing to generate 8-bit UUID
public String[] chars = new String[] { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" }; public String getShortUuid() { StringBuffer stringBuffer = new StringBuffer(); String uuid = UUID.randomUUID().toString().replace("-", ""); for (int i = 0; i < 8; i++) { String str = uuid.substring(i * 4, i * 4 + 4); int strInteger = Integer.parseInt(str, 16); stringBuffer.append(chars[strInteger % 0x3E]); } return stringBuffer.toString(); } @Test public void test4(){ TestDemo2 testDemo2 = new TestDemo2(); System.out.println(UUID.randomUUID().toString()); System.out.println(testDemo2.getShortUuid()); }
output
4880d2b4-bc5f-48d1-ba58-003334276d46 M3EeoAYr
Version three
Timestamp plus generated 8-bit UUID
@Test public void test3() { TestDemo2 testDemo2 = new TestDemo2(); String shortUuid = testDemo2.getShortUuid(); String create_time = new SimpleDateFormat("yyyyMMddHHmmss").format(new Date()); System.out.println(create_time+shortUuid); }
output
20190925101216hh42xxn6
It is recommended to use the timestamp plus the generated 8-bit UUID
oracle generates unique identity
Version 1
Unique identification of serial number generation
Create sequence
-- Create sequence create sequence SEQ_ORDER_ID minvalue 100000 maxvalue 999999 start with 414591 increment by 1 nocache cycle;
| field | Explain |
|---|---|
| minvalue | Define the minimum value that a sequence generator can produce |
| maxvalue | Define the maximum value that a sequence generator can produce |
| start with | Defines the initial value of the sequence (that is, the first value generated), which is 1 by default |
| increment by | Defines the step size (increment) of the sequence. If omitted, it defaults to 1. If a negative value appears, the value of the sequence is decremented according to this step size |
| nocache | Indicates that the sequence is not buffered in memory |
| cycle | Indicates whether to loop when the value of the sequence generator reaches the limit value. CYCLE means CYCLE, NOCYCLE means no CYCLE |
Get serial number
SELECT SEQ_ORDER_ID.NEXTVAL FROM DUAL;
output
414785
Version two
Time stamp plus serial number
SELECT TO_CHAR(SYSDATE,'YYYYMMDDHH24MISS')||SEQ_ORDER_ID.NEXTVAL FROM DUAL;
output
20190925102115414805
Time stamp plus serial number is recommended
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