Counting
?!
4 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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5 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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A simple counting
problem
6 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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The Rules:
1. Only one number
2. Convince me it's correct
7 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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How many friends
do you have?
8 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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Will I get the same number if...
!"#$
I ask every person you know if they consider you
their friend?
9 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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Will I get the same number if...
! "
I ask every person that knows you if they think you
would consider them a friend?
10 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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Is this the number of people that you'd tell
a secret to?
11 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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But it depends!!
12 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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How many users do we
have?
13 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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SELECT COUNT(*) FROM prod.users
14 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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user_id name email deleted
1 Alice alice@***
2 Bob bob@*** true
3 Carol
15 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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SELECT COUNT(*)
FROM prod.users
WHERE deleted != true
AND email != null
16 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw
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SELECT COUNT(*)
FROM prod.users
WHERE last_active > 2017-07-24
17 — WriteSpeakCode 2017 | Ronnie Chen @rondoftw