From 5abfc19c744aaa6d1b2a0cc4cc8db910fab71e2b Mon Sep 17 00:00:00 2001 From: mba1398 <26516464+mba1398@users.noreply.github.com> Date: Sat, 25 Sep 2021 22:28:25 +0800 Subject: [PATCH] =?UTF-8?q?Update=20ch08:=20=E7=A7=8B=E6=8B=9B=E7=A7=98?= =?UTF-8?q?=E7=B1=8D=20C.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ch08: 秋招秘籍 C.md | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/ch08: 秋招秘籍 C.md b/ch08: 秋招秘籍 C.md index 73d3034..9c951b8 100644 --- a/ch08: 秋招秘籍 C.md +++ b/ch08: 秋招秘籍 C.md @@ -72,13 +72,16 @@ INSERT INTO t_act_records VALUES('u1004', 20210105); # 练习四:hive 数据倾斜的产生原因及优化策略? -# 练习五:假设 A表有5行(关联列 name 有2行为空),B表有6行(关联列 name 有3行为空)那么 A left join B on A.name = B.name 会返回多少行结果? +# 练习五:left join 是否会出现多出的行? +假设 A表有5行(关联列 name 有2行为空),B表有6行(关联列 name 有3行为空)那么 A left join B on A.name = B.name 会返回多少行结果? + 可以参考下图 A表 -[]() + +[A表](./img/Question_C/C05A.jpg) B表 -[]() +[B表](./img/Question_C/C05B.jpg)