使用 PostgreSQL 更新只读列时引发异常

Question

我试图在修改只读列时引发异常。为此，我在更新前使用了触发器，但出现语法错误。

DROP TRIGGER IF EXISTS check_update_guid_line ON line;
CREATE TRIGGER check_update_guid_line
    BEFORE UPDATE ON line FOR EACH ROW
    WHEN (OLD.guid IS DISTINCT FROM NEW.guid) THEN
      RAISE EXCEPTION 'you cant modify the guid of a line');

ERROR: syntax error at or near "THEN" LINE 29: ...OLD.guid IS DISTINCT FROM NEW.guid) THEN

我想我可以制作一个扩展代码的过程，但我想知道为什么这段代码无论如何都不起作用。

Answer 1

将其分为两步，如下所示：

CREATE OR REPLACE FUNCTION fn_1()
 RETURNS trigger
 LANGUAGE plpgsql
 COST 1
AS $function$
BEGIN
  IF NEW.id is distinct from OLD.id then
    RAISE EXCEPTION '%','whatever it is';
  END IF;
  return NEW;
END;
$function$
;

CREATE TRIGGER tgr
    BEFORE UPDATE ON line
    FOR EACH ROW
    EXECUTE PROCEDURE fn_1();

使用 PostgreSQL 更新只读列时引发异常

Raise exception on update of read only column with PostgreSQL

sql

postgresql

syntax-error

database-trigger