那就再把值转成字符串拼接一个"%"号
SELECT b.system,
CAST(CAST(b.per / a.total AS DECIMAL(10, 3)) * 100 AS VARCHAR(10)) + '%' AS '各系统使用率%'
FROM (SELECT COUNT(*) AS total FROM tb_room_network_info) a,
(SELECT system, COUNT(f_id) AS per
FROM tb_room_network_info
GROUP BY system) b;
有问题追问
查询借书表中只借一次的图书编号,然后根据图书编号查询图书信息
select *
from
book
where
BNO
=（
SELECT
BNO
count(BNO) FROM
borrow
where
count(BNO)=1）
这样试试
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