在oracle中使用Sequence.NextVal创建表[重复]

Question

create sequence qname_id_seq start with 1 increment by 1 nocache;

Error report:
SQL Error: ORA-00907: missing right parenthesis
00907. 00000 -  "missing right parenthesis"

我使用以下查询创建了一个带有Sequence.NextVal的表，

CREATE TABLE qname
(
    qname_id integer NOT NULL default qname_id_seq.nextval PRIMARY KEY,
    qname    VARCHAR2(4000) NOT NULL -- CONSTRAINT qname_uk UNIQUE
);

Answer 1

像许多其他数据库一样，我们现在终于有了Identity列，在这种情况下，序列是在幕后自动生成的。这个解决方案比基于触发器的解决方案要快得多，可以在这篇博客文章中看到。

因此，您的表创建如下所示：

CREATE TABLE qname
(
    qname_id integer GENERATED BY DEFAULT AS IDENTITY (START WITH 1) NOT NULL PRIMARY KEY,
    qname    VARCHAR2(4000) NOT NULL -- CONSTRAINT qname_uk UNIQUE
);

根据文档，您不能这样做：

CREATE OR REPLACE TRIGGER my_trigger
  BEFORE INSERT 
  ON qname
  FOR EACH ROW
  -- Optionally restrict this trigger to fire only when really needed
  WHEN (new.qname_id is null)
DECLARE
  v_id qname.qname_id%TYPE;
BEGIN
  -- Select a new value from the sequence into a local variable. As David
  -- commented, this step is optional. You can directly select into :new.qname_id
  SELECT qname_id_seq.nextval INTO v_id FROM DUAL;

  -- :new references the record that you are about to insert into qname. Hence,
  -- you can overwrite the value of :new.qname_id (qname.qname_id) with the value
  -- obtained from your sequence, before inserting
  :new.qname_id := v_id;
END my_trigger;