MySQL 行列轉換

最近在慕課上 看mysql教程 裡面關於行轉列的教程不錯 貼上練習sql 做個記錄

簡單行轉列

select

a.user_name,
sum(b.kills)
from
user1 a
join user_kills b on a.id = b.user_id
group
by    user_name;

select * from (

select
sum(kills) as
'孫悟空'
from
user1 a
join user_kills b on a.id = b.user_id
and a.user_name = '孫悟空'
) across
join (
select
sum(kills) as
'沙甥'
from
user1 a
join user_kills b on a.id = b.user_id
and a.user_name = '沙甥'
) bcross
join (
select
sum(kills) as
'豬八戒'
from
user1 a
join user_kills b on a.id = b.user_id
and a.user_name = '豬八戒'
) c;

case行列轉換

select

sum(
case
when user_name = '孫悟空'
then
kills
end) as
'孫悟空',
sum(
case
when user_name = '沙甥'
then
kills
end) as
'沙甥',
sum(
case
when user_name = '豬八戒'
then
kills
end) as
'豬八戒'
from
user1 a
join user_kills b on a.id = b.user_id;

select

user_name,
replace (
substring(
substring_index(mobile, ',', a.id),
char_length(
substring_index(mobile, ',', a.id - 1)
) + 1
),',',
'') as mobile
from
tb_sequence a
cross
join (
select
user_name,
concat(mobile, ',') as mobile,
length(mobile) - length(replace(mobile, ',', '')) + 1
size
from
user1 b
) b on a.id <= b.size;

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