Sequence numbers are used by SQL statements that reference the sequence. You can issue a statement to generate a new sequence number or use the current sequence number. After a statement in a user's session generates a sequence number, the particular sequence number is available only to that s...
使用cache或许会跳号, 比如数据库突然不正常down掉(shutdown abort),cache中的sequence就会丢失. 所以可以在create sequence的时候用nocache防止这种情况。 2、Alter Sequence 你或者是该sequence的owner,或者有ALTER ANY SEQUENCE 权限才能改动sequence. 可以alter除start至以外的所有sequence参数.如果想要改变start值,必须...
代码运行次数:0 ORDERguarantees that sequence numbers are generatedinorderofrequest.You may want to usethisoptionifyou are using the sequence numbersastimestamps.Guaranteeing order is usually not importantforsequences used to generate primary keys.NOORDERdoes not guarantee sequence numbers are generatedin...
在这里面tom大师说了,sequence的唯一的用处是保证数值的唯一性,既不保证gap free,也不保证order。 you cannot expect a sequence to return gap free values. a sequence has one purpose: assign unique numbers to stuff. Nothing else. there will be gaps, gaps are normal, expected, good, ok, fine. t...
In case of a system failure event, you will lose all cached sequence values that have not been used in committed SQL statements. ORDER Use ORDER to ensure that Oracle will generate the sequence numbers in order of request. This option is useful if you are using Oracle Real Application Clus...
你在中间有一个间隙，重新设置序列不会解决这个问题。序列将generate a gap free sequence of numbers，...
ORDERNOORDERif you do not want to guarantee sequence numbers are generated in order of request. This is the default. 查看user_sequences 表的结构: SQL> desc user_sequences; 名称 是否为空? 类型 --- --- --- SEQUENCE_NAME NOT NULL VARCHAR2(30) MIN_VALUE NUMBER MAX_VALUE ...
sequence_name.CURRVALsequence_name.NEXTVAL After creating a sequence, you can use it to generate unique sequence numbers for transaction processing. However, you can useCURRVALandNEXTVALonly in aSELECTlist, theVALUESclause, and theSETclause. In the following example, you use a sequence to insert ...
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Instead of grouping rows into fixed size intervals, you may want to combine all rows that fall within twenty minutes of the previous. This could lead to intervals of any size! The SQL pattern matching method for this is: Copy code snippet ...