拼接字段返回字符串
SELECT GROUP_CONCAT(field_id) FROM your_table
NOT EXISTS 子查询筛选目标记录集
SELECT * FROM `main_table` a WHERE NOT EXISTS(SELECT id FROM `sub_table` WHERE id=a.tid and `day`='20200517') LIMIT 50
find_in_set()函数使用
select * from article where FIND_IN_SET('4',type)
使用时间戳赚日期函数 方便分组 from_unixtime 第二个参数是转换格式
"SELECTdateline,from_unixtime(dateline,'%Y%m') as `date`,count(*) as num FROM threads WHERE dateline between {$start} and {$end} GROUP BY `date` "
将数据库字段数值转换为绝对值
SELECT abs(price) as abs_price,price,count(*) as num FROM threads WHERE dateline between {$start} and {$end} GROUP BY `abs_price` HAVING abs_price between {$start_reward} and {$end_reward}"
由于 where 执行条件在前 因此 通过 as 别名生成的临时字段无法在where中使用 如果真的需要使用该字段做筛查 可以如下
1. 使用子查询
2.分组后结合 having 查询
查看 表结构
desc table_xxx
show create table table_xxx
列举符合条件的数据表
show TABLES like 'table_%'