Question

我希望能够跟踪表格中相关记录的历史记录。在Oracle系统上，我通过创建一个插入触发器来完成此操作，该触发器将使用原始记录的PK（如果已知）填充字段，或者如果未指定原始PK则使用新PK填充。

换句话说，给定以下代码，INS_Nomination触发器将使用传入的parent_nomination_id填充新的Nomination.parent_nomination_id字段，或者如果parent_nomination_id为NULL，则填充为表的PK（nomination_id）生成的值：

/*create nomination tables*/
    CREATE TABLE Nomination (
        nomination_id NUMBER(12,0) NOT NULL ENABLE, 
        parent_nomination_id NUMBER(12,0) NOT NULL, 
        whatever VARCHAR2(400 BYTE), 
        created_by NUMBER(12,0) NOT NULL ENABLE, 
        created_date DATE DEFAULT SYSDATE NOT NULL ENABLE, 
        active_ind NUMBER(1,0) DEFAULT 1 NOT NULL ENABLE, 
        CONSTRAINT Nomination_PK PRIMARY KEY (nomination_id) ENABLE
    );

    CREATE INDEX Nomination_INDEX1 ON Nomination (parent_nomination_id, active_ind DESC) ;

    CREATE UNIQUE INDEX Nomination_PK ON Nomination (nomination_id);

    CREATE SEQUENCE Nomination_SEQ;

    CREATE OR REPLACE TRIGGER INS_Nomination BEFORE INSERT ON Nomination FOR EACH ROW 
    BEGIN   
        SELECT Nomination_SEQ.nextval
        INTO :new.nomination_id 
        FROM Dual;

        SELECT NVL(:NEW.parent_nomination_id, :NEW.nomination_id)
        INTO :NEW.parent_nomination_id
        FROM Dual;
    END;

    /
    ALTER TRIGGER INS_Nomination ENABLE;

如何使用Postgres完成相同的功能？

Answer 1

DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;

CREATE TABLE nomination 
      ( nomination_id BIGSERIAL NOT NULL PRIMARY KEY
      , parent_nomination_id BIGINT NOT NULL
         REFERENCES nomination(nomination_id)
      , whatever VARCHAR
      , created_by INTEGER NOT NULL DEFAULT 0
      , created_date DATE NOT NULL DEFAULT CURRENT_DATE
      , active_ind boolean NOT NULL DEFAULT true
    );

CREATE OR REPLACE FUNCTION nomination_fix_parent() RETURNS TRIGGER
AS
$func$
        BEGIN
         NEW.parent_nomination_id := NEW.nomination_id ;
         RETURN NEW;
        END
$func$ LANGUAGE plpgsql ; 

CREATE TRIGGER nomination_fix_parent
    BEFORE INSERT ON nomination
    FOR EACH ROW
    WHEN (NEW.parent_nomination_id IS NULL)
    EXECUTE PROCEDURE nomination_fix_parent()
        ; 

-- Test it ...
INSERT INTO nomination(whatever) VALUES('First?' );
INSERT INTO nomination(parent_nomination_id, whatever) VALUES(1,'Second?' );
INSERT INTO nomination(nomination_id, parent_nomination_id, whatever) VALUES(5,1,'Five?' );
SELECT * FROM nomination;

-- after entering the third record with id=5, the sequence is out of sequence ...
SELECT currval('nomination_nomination_id_seq');

-- Re-adjust the value for the sequence
SELECT setval('nomination_nomination_id_seq', (SELECT MAX(nomination_id) FROM nomination) );

INSERT INTO nomination(whatever) VALUES('Fourth?' );
SELECT * FROM nomination;

注意：

PRIMARY KEY和REFERENCES子句会自动为您创建索引
SERIAL和BIGSERIAL自动创建序列，并将其nextval（）用作默认值
所以上面片段中的触发器只需要为parent_nomination_id设置DEFAULT，而不是基于序列，而是在同一行的nomination_id上（可能是基于序列）。
手动将值插入SERIAL / bigserial列不会碰撞序列;所以你必须事后重新同步（使用setval('nomination_id_seq', select max() from ...)）。

PostgreSQL触发器用序列值填充NULL非PK字段

1 个答案: