分享一条大神写的sql，查询所有数据，每条数据附带前一条指定列：
SELECT
f.ts_code,
@prev AS pre_adj_factor,
f.trade_date,
@prev := f.adj_factor AS adj_factor
FROM
( SELECT @prev := NULL ) AS i,
syn_factors AS f
WHERE
ts_code = '000001.SZ'
ORDER BY
f.trade_date
