检查 `RECORD` 变量是否已初始化

Question

我正在尝试声明一个数据类型为 record 的变量，但是当没有结果可以用来填充它时我遇到了麻烦。下面是函数的简化模型：

    CREATE OR REPLACE FUNCTION do_something()
        RETURNS TRIGGER AS $$
    DECLARE
        engagement record;
    BEGIN
        SELECT code
        INTO engagement
        FROM "mainEngagement" me
        WHERE me.value = NEW.id;

        IF TG_OP = 'INSERT'
        THEN
            INSERT INTO engagement_details (code)
            values (
                case
                    when engagement is not null
                        then exists(select code from engagement where "value" = 'expected')
                    else false
                end
            );
        ELSE
            UPDATE engagement_details
            SET
                code = case
                    when engagement is not null
                        then exists(select 1 from engagement where "value" = 'expected')
                    else false
                end
            WHERE engagement_details.assessment_id = NEW.id;
        END IF;

        RAISE NOTICE 'Updated engagement_details: [%]', NEW;
        RETURN NEW;
    END;
    $$ LANGUAGE plpgsql;

当触发器运行且 "mainEngagement" 中没有数据时，我在 INSERT 中收到错误：

ERROR: relation "engagement" does not exist

我找不到测试参与度是否已填充的方法。我搜索了很多堆栈溢出问题，但大多数人只是建议做 engagement := row(null)，但 when engagement is not null 仍然对我不起作用。

Answer 1

使用IF NOT FOUND:

SELECT code
INTO engagement
FROM "mainEngagement" me
WHERE me.value = NEW.id;

IF NOT FOUND
THEN
    RAISE WARNING '|W| do_something(): engagement undefined';    -- report warning
    RETURN;    -- exit early, function cannot proceed
END IF;

Answer 2

我在这里遇到的问题是 RECORD 条目只能有一行作为结果。我试图 return 一个包含多行的值，然后运行记录上的 CASE 语句，这永远行不通。而是执行以下操作：

    CREATE OR REPLACE FUNCTION do_something()
        RETURNS TRIGGER AS $$
    DECLARE
        engagement boolean;
    BEGIN
        SELECT EXISTS (
            SELECT 1 FROM engagement WHERE "value" = 'expected'
        ) INTO engagement;

        IF TG_OP = 'INSERT'
        THEN
            INSERT INTO engagement_details (code)
            values (engagement);
        ELSE
            UPDATE engagement_details
            SET
                code = engagement
            WHERE engagement_details.assessment_id = NEW.id;
        END IF;

        RAISE NOTICE 'Updated engagement_details: [%]', NEW;
        RETURN NEW;
    END;
    $$ LANGUAGE plpgsql;

更简单、更清晰且有效。

检查 `RECORD` 变量是否已初始化

Check if a `RECORD` variable is initialized

postgresql

plpgsql