数据库函数-常用的MySQL函数

1.date_sub() 时间的加减

　　备注：record 为datetime类型

   　　 select
            record_time as date,
            order_area as  orderArea,
            order_cnt as orderCnt
        from
            dm_rpt_dss_enterprise_sum
        where
             seller_enterprise_id = #{enterpriseId}
             and
             record_time between  date_sub(#{date},interval 15 day) and  #{date}
        group by
            record_time
        order by
            record_time

2.date_format() 时间日期格式化

　　备注：record 为datetime类型

select
            DATE_FORMAT(record_time, '%Y-%m-%d') recordTime,
            permeability ,
            orderincrement_30d as orderincrement30d,

            active_rate as activeRate,
            noorder_increment_90d as noorderIncrement90d,
            noorder_increment_30_90d as noorderIncrement30_90d,

            coverage_rate as coverageRate,
            ptial_cus_excavablearea as ptialCusExcavablearea,
            clue_cus_excavablearea as clueCusExcavablearea
 from
            dm_rpt_dss_enterprise_sum

3. now（）获取当前时间

4.IFNULL() 处理值为null的情况

SELECT
            count(distinct customer_id) as customerNum,
            IFNULL( SUM(influence_quantity),0.00)  as influenceQuantity
FROM 
　　　　　　　customer_early_warning
WHERE 
　　　　　　　to_days(record_time) = to_days(now())
　　　　　　  AND seller_enterprise_id = #{sellerEnterpriseId}

5.convert() 转换函数

IFNULL( CONVERT ( d.orderArea / 10000, DECIMAL ( 18, 2 ) ), 0.00 ) AS orderArea

 6.concat() 字符串拼接函数

 CONCAT( province, '^', city, '^', area ) AS area

 7.substr() 字符串截取

SUBSTR( a.record_time, 1, 10 ) >= concat( substr( #{queryDTO.queryDate}, 1, 7 ), '-01' )