-- 示例:多步骤计算用户留存率
WITH
first_purchases AS (SELECT customer_id,MIN(purchase_date) AS first_purchase_dateFROM purchasesGROUP BY customer_id
)
,
monthly_active_users AS (SELECT DATE_FORMAT(purchase_date, %Y-%m-01) AS month ,COUNT(DISTIN…
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接之前 blog 【OS】【Nuttx】【构建】cm…
引用类型1、string字符串类型:1.1、作用:字符串类型,用于存储多个字符1.2、创建方式:(1)完整写法:char[] chars { a, b, c };
string str new String(chars);(2…