1、char_length() 求字符串的长度

select tweet_id from tweets where char_length(content) > 15

2、性能问题

这两个sql到底是按个更快一点？

Sql1

select customer_id, count(visit_id) as count_no_trans 
from visits where visit_id not in (
    select distinct visit_id from transactions
)
group by customer_id

Sql2

select a.customer_id, count(a.customer_id) as count_no_trans 
from visits a 
left join transactions b on a.visit_id = b.visit_id
where b.transaction_id is null
group by a.customer_id;

3、datediff(date1, date2)获取时间差

select a.id from weather as a 
join weather as b on datediff(a.recordDate, b.recordDate) = 1  
-- 这里datediff(a.recordDate, b.recordDate) = 1就表示a.date - b.date = 1
where a.temperature > b.temperature;

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• a2d3a-

  feat(wiki): hammeSpoon: 复制出来的文件需要重新生成永链

  On 3/27/25