sql条件语句

1. sql中的if–else语句

case when 'a' then 'b' else 'c' end 
-- 若a为空则设置code为指定值
case when a is not null then a else '0000000000' end as code
case when a is null then '0000000000' else a end as code

2. 筛选数据

where... (比较运算符）
where... in (...,...,...,)
where... like '..%...%..'
where... group by .. having...