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add explanation to approx_count_distinct #10627
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add explanation to approx_count_distinct
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@@ -35,7 +35,8 @@ TiFlash 支持部分算子的下推,支持的算子如下: | |||
* 日期函数:`date_format, timestampdiff, from_unixtime, unix_timestamp(int), unix_timestamp(decimal), str_to_date(date), str_to_date(datetime), datediff, year, month, day, extract(datetime), date, hour, microsecond, minute, second, sysdate, date_add, date_sub, adddate, subdate, quarter, dayname, dayofmonth, dayofweek, dayofyear, last_day, monthname, to_seconds, to_days, from_days, weekofyear` | |||
* JSON 函数:`json_length` | |||
* 转换函数:`cast(int as double), cast(int as decimal), cast(int as string), cast(int as time), cast(double as int), cast(double as decimal), cast(double as string), cast(double as time), cast(string as int), cast(string as double), cast(string as decimal), cast(string as time), cast(decimal as int), cast(decimal as string), cast(decimal as time), cast(time as int), cast(time as decimal), cast(time as string), cast(time as real)` | |||
* 聚合函数:`min, max, sum, count, avg, approx_count_distinct, group_concat` | |||
* 聚合函数:`min, max, sum, count, avg, group_concat` | |||
* 聚合函数(近似算法):`approx_count_distinct` (功能同 `count`,计算速度有数量级的提升,但可能带来 1% ~ 5% 的误差。适合对精度要求不高的大量数据做快速统计。) |
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功能上是 COUNT(DISTINCT) 近似结果
PR needs rebase. Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. |
Removed the needs-cherry-pick-release-6.6 label because the v6.6 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.6 and will no longer receive new updates. |
First-time contributors' checklist
What is changed, added or deleted? (Required)
add explanation to approx_count_distinct
Which TiDB version(s) do your changes apply to? (Required)
Tips for choosing the affected version(s):
By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.
For details, see tips for choosing the affected versions (in Chinese).
What is the related PR or file link(s)?
Do your changes match any of the following descriptions?