mysql中sql块的用法：1、进行非默认的排序；2、更新替换某一个字段中的特定字符串【SELECT a.id FROM(..)】；3、求比例的sql【b.num / a.sum * 100】。

mysql中sql块的用法：

1、使用非默认的排序，例如使用213之类的排序

可以使用如下方法

SELECT DISTINCT
pg.part_grp_id,
pg.part_grp_name,
pg.equip_category_id
FROM
cost_part_grp pg,
cost_part_kit pk,
cost_part_event pe
WHERE
pe.mdl_ver_id IN (
SELECT
s.mdl_ver_id
FROM
cost_fleet_model s
WHERE
s.fleet_id = 1002
)
AND pe.part_kit_id = pk.part_kit_id
AND pk.part_grp_id = pg.part_grp_id
ORDER BY
CASE pg.equip_category_id
WHEN 2 THEN
1
WHEN 1 THEN
2
WHEN 4 THEN
3
ELSE
4
END

2、mysql更新替换某一个字段中的特定字符串

UPDATE t_bss_employees
SET mobilephone = REPLACE (mobilephone, "2129", "0000")
WHERE
id IN (
SELECT
a.id
FROM
(
SELECT
id
FROM
t_bss_employees
WHERE
mobilephone IN (
'18121299262',
'18121299247',
'18121299206',
'18121299209'
)
) AS a
)

将mobilephone字段中的2129字符串替换为0000

使用当前表为条件更新当前表。需要在条件处再添加一个（）构建一个虚拟表

3、求比例的sql

select a.style, ROUND(
            b.num / a.sum * 100,
            2
        ) as styleRate from (SELECT 
count(qspc.id) sum 
,qq.style  style
from  t_qc_security_plan_comment  qspc 
inner join t_qc_question qq
on qq.id = qspc.question_id
LEFT JOIN t_qc_address qa ON qa.id = qspc.address_id
LEFT JOIN t_system_organ  so on qa.hospital =  so.id
WHERE qq.scr_level is not NULL
and qq.type = 3  and so.tenant_code = 'zzyy'
GROUP BY style) a left join (SELECT 
count(qspc.id) num 
,qq.style  style
from  t_qc_security_plan_comment  qspc 
inner join t_qc_question qq
on qq.id = qspc.question_id
LEFT JOIN t_qc_address qa ON qa.id = qspc.address_id
LEFT JOIN t_system_organ  so on qa.hospital =  so.id
WHERE qq.scr_level is not NULL
and qq.type = 3  and so.tenant_code = 'zzyy'
and qspc.is_bad =0
GROUP BY style) b on a.style = b.style

计算逻辑是分别求总数和平均数。然后两数相除再用round求精度