Question

根据我在PostgreSQL（9.3）How to check a sequence efficiently for used and unused values in PostgreSQL中的上一个问题，我现在有一个table chart_gap，其中包含表格图表中所有未使用的图表编号的列表：

CREATE TABLE chart_gap (chart_number integer);

在尝试更多地理解触发器时，我添加了以下触发器程序或多或少地从该问题中采取：

CREATE OR REPLACE FUNCTION next_chart() RETURNS trigger AS $BODY$
BEGIN
  -- Check for empty chart number
  IF NEW.chart_number IS NULL THEN

    WITH ins AS (
      SELECT chart_number
      FROM   chart_gap
      WHERE  pg_try_advisory_xact_lock(chart_number)
      LIMIT  1
    )
    DELETE FROM chart_gap c
    USING  ins i
    WHERE  i.chart_number = c.chart_number;

    NEW.chart_number := select chart_number from ins;   <--WRONG!       
  END IF;

  RETURN NEW;
END;
$BODY$ LANGUAGE plpgsql VOLATILE;

触发程序与图表文件绑定：

CREATE TRIGGER next_chart
  BEFORE INSERT
  ON charts
  FOR EACH ROW
  EXECUTE PROCEDURE next_chart();

我想要做的是在添加新图表记录时替换图表中的空图表编号字段。这可以在触发器中完成吗？（还有什么是正确的语法??）

Answer 1

在CREATE FUNCTION next_chart() RETURNS trigger AS $BODY$ BEGIN -- Check for empty chart number IF NEW.chart_number IS NULL THEN WITH ins AS ( SELECT chart_number FROM chart_gap WHERE pg_try_advisory_xact_lock(chart_number) LIMIT 1 ) DELETE FROM chart_gap c USING ins i WHERE i.chart_number = c.chart_number RETURNING i.chart_number INTO NEW.chart_number; END IF; RETURN NEW; END; $BODY$ LANGUAGE plpgsql VOLATILE;函数中，您可以使用query RETURNING ... INTO ...，如下所示：

.headline {
  float: right;
}
.btn {
  float: left;
}

如何从PostgreSQL中的cte返回触发器中的新值

1 个答案: