生成唯一随机数

# 非补0版本

SELECT FLOOR(100000 + RAND() * 899999) AS random_number

FROM target_table

WHERE "unique_field" NOT IN (SELECT unique_field FROM target_table)

LIMIT 1  

# 补0版本

SELECT LPAD(FLOOR(RAND() * 999999), 6, 0) AS random_number

FROM target_table

WHERE "unique_field" NOT IN (SELECT unique_field FROM target_table)

LIMIT 1