-- 应收账单转单号快照迁移
-- 适用于已经执行过 ar/ar_bill.sql 的存量数据库。
-- 本脚本可重复执行，不删除账单明细，不覆盖已经存在的转单号快照。
SET NAMES utf8mb4;
SET @db_name := DATABASE();

-- 1. 账单明细保存生成账单时的转单号快照。
SET @has_transfer_no := (
    SELECT COUNT(*)
    FROM information_schema.COLUMNS
    WHERE TABLE_SCHEMA = @db_name
      AND TABLE_NAME = 'ar_bill_detail'
      AND COLUMN_NAME = 'transfer_no'
);
SET @sql := IF(@has_transfer_no = 0,
    'ALTER TABLE ar_bill_detail ADD COLUMN transfer_no VARCHAR(64) DEFAULT NULL COMMENT ''转单号快照'' AFTER tracking_no',
    'SELECT 1');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

-- 2. 详情按账单查询转单号时使用组合索引。
SET @has_transfer_index := (
    SELECT COUNT(*)
    FROM information_schema.STATISTICS
    WHERE TABLE_SCHEMA = @db_name
      AND TABLE_NAME = 'ar_bill_detail'
      AND INDEX_NAME = 'idx_ar_bill_detail_bill_transfer_no'
);
SET @sql := IF(@has_transfer_index = 0,
    'ALTER TABLE ar_bill_detail ADD KEY idx_ar_bill_detail_bill_transfer_no (ar_bill_id, transfer_no)',
    'SELECT 1');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

-- 3. 历史数据尽力回填，仅填充空值，不覆盖账单生成时已经保存的快照。
--    如果来源订单后续修改过转单号，回填值仅代表当前来源表值，不能视为严格历史值。
UPDATE ar_bill_detail d
JOIN prc_order_bill p ON p.bill_id = d.prc_order_bill_id
SET d.transfer_no = p.transfer_no
WHERE d.transfer_no IS NULL
  AND p.transfer_no IS NOT NULL;

-- 4. 执行后核验字段和回填数量。
SELECT
    COUNT(*) AS detail_count,
    SUM(CASE WHEN transfer_no IS NOT NULL AND TRIM(transfer_no) <> '' THEN 1 ELSE 0 END) AS transfer_no_count
FROM ar_bill_detail;