mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-10-19 15:01:03 +00:00
22f51f103c
* CLICKHOUSE-4063: less manual html @ index.md * CLICKHOUSE-4063: recommend markdown="1" in README.md * CLICKHOUSE-4003: manually purge custom.css for now * CLICKHOUSE-4064: expand <details> before any print (including to pdf) * CLICKHOUSE-3927: rearrange interfaces/formats.md a bit * CLICKHOUSE-3306: add few http headers * Remove copy-paste introduced in #3392 * Hopefully better chinese fonts #3392 * get rid of tabs @ custom.css * Apply comments and patch from #3384 * Add jdbc.md to ToC and some translation, though it still looks badly incomplete * minor punctuation * Add some backlinks to official website from mirrors that just blindly take markdown sources * Do not make fonts extra light * find . -name '*.md' -type f | xargs -I{} perl -pi -e 's//g' {} * find . -name '*.md' -type f | xargs -I{} perl -pi -e 's/ sql/g' {} * Remove outdated stuff from roadmap.md * Not so light font on front page too * Refactor Chinese formats.md to match recent changes in other languages * Update some links on front page * Remove some outdated comment * Add twitter link to front page * More front page links tuning * Add Amsterdam meetup link * Smaller font to avoid second line * Add Amsterdam link to README.md * Proper docs nav translation * Back to 300 font-weight except Chinese * fix docs build * Update Amsterdam link
1.8 KiB
1.8 KiB
Float32, Float64
浮点数。
类型与以下 C 类型是相同的:
Float32
-float
Float64
-double
我们建议,如果可能的话尽量用整形来存储数据。比如,将一定精度的浮点数转换成整形,譬如货币金额或者毫秒单位的加载时间。
使用浮点数
-
对浮点数进行计算可能引起四舍五入的误差。
SELECT 1 - 0.9
┌───────minus(1, 0.9)─┐ │ 0.09999999999999998 │ └─────────────────────┘
-
计算的结果取决于计算方式(处理器类型和计算机系统架构)
-
浮点数计算可能出现这样的结果,比如 "infinity" (
Inf
) 和 "not-a-number" (NaN
)。对浮点数计算的时候应该考虑到这点。 -
当一行行阅读浮点数的时候,浮点数的结果可能不是机器最近显示的数值。
NaN 和 Inf
相比于 SQL,ClickHouse 支持以下几种浮点数分类:
-
Inf
– 正无穷。SELECT 0.5 / 0
┌─divide(0.5, 0)─┐ │ inf │ └────────────────┘
-
-Inf
– 负无穷。SELECT -0.5 / 0
┌─divide(-0.5, 0)─┐ │ -inf │ └─────────────────┘
-
NaN
– 非数字。SELECT 0 / 0
┌─divide(0, 0)─┐ │ nan │ └──────────────┘
可以在ORDER BY 子句 查看更多关于 NaN
排序的规则。