PostgreSQL中的自定义自动递增字段(发票/订单号)

基线要求是以以下格式创建订单号:

(M)M-SSS

其中MM表示当前月份，SSSS表示该月份的订单顺序.例如1-002将代表一月份提交的第二个订单.

Where MM represents the current month and SSSS represents the order sequence for that month. For example 1-002 would represent the second order submitted in January.

使用触发器，我希望自动递增并透明地插入.

Using a TRIGGER I'd like the auto-increment and insert to work transparently.

不幸的是，距离我接触存储过程已经很长时间了，这是我第一次尝试Postgresql.指出正确方向的任何帮助将不胜感激.

Unfortunately, it has been a long time since I have touched a stored procedure and this is my first foray into postgresql. Any help pointing in the right direction would be greatly appreciated.

更新:这是使用@peterm的代码的最终实现

-- The trigger
CREATE TRIGGER add_order_number 
   BEFORE INSERT ON orders FOR EACH ROW
   EXECUTE PROCEDURE order_number_update();

-- The trigger function
CREATE FUNCTION order_number_update() RETURNS TRIGGER AS $$
DECLARE
    next_order TEXT;
BEGIN
    -- get the next order number
    SELECT INTO next_order CONCAT(CAST(DATE_PART('MONTH', CURRENT_DATE) AS VARCHAR(2)),
       '-', 
       LPAD(CAST(COALESCE(CAST(RIGHT(MAX(order_number), 3) AS INT), 0) + 1 AS VARCHAR(3)), 3, '0'))
    FROM orders
    WHERE CAST(LEFT(order_number, STRPOS(order_number, '-') - 1) AS INT) = DATE_PART('MONTH', CURRENT_DATE);

    -- update the field
    NEW.order_number = next_order;
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

注意:通过将更新添加为INSERT触发器之前，它可以完全透明且可预测的方式运行，就像正常的SERIAL或BIGSERIAL字段一样.