mysql中的数据透视表 [英] pivot table in mysql
本文介绍了mysql中的数据透视表的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我知道如何在mysql中创建数据透视表(请参见下面的代码示例),但是如果数据透视表中的列数非常大并且我不想键入2000左右的标记名怎么办? -有没有一种方法可以生成该列表? 预先非常感谢.
I know how to make a pivot table in mysql (see code example below), but what if the number of columns in the pivot table is very large and I don't want to type 2000 or so tagnames? - Is there a way to have that list generated? Many thanks in advance.
drop table pivot;
create table pivot SELECT time,
max(if(tagname = 'a', value, null)) AS 'a',
max(if(tagname = 'b', value, null)) AS 'b',
max(if(tagname = 'c', value, null)) AS 'c'
FROM test where tagname in ('a','b','c')
GROUP BY time;
select * from pivot;
推荐答案
您始终可以创建一个完全可以做到这一点的shell脚本:-)
You can always create a shell script that does exactly that :-)
#!/bin/sh
mysql -BN test > /tmp/$$_tagnames.tmp <<SQL
select distinct tagname from test;
SQL
cat > /tmp/$$_create_table.sql <<EOF
drop table if exists pivot;
create table pivot select
EOF
while read tag; do
echo "max(if(tagname = '$tag', value, null)) AS '$tag'," >> /tmp/$$_create_table.sql
done < /tmp/$$_tagnames.tmp
cat >> /tmp/$$_create_table.sql <<EOF
time
FROM test
GROUP BY time;
select * from pivot;
EOF
mysql -Bt test < /tmp/$$_create_table.sql
rm /tmp/$$_create_table.sql
rm /tmp/$$_tagnames.tmp
数据:
Data:
mysql> select * from test;
+---------+-------+---------------------+
| tagname | value | time |
+---------+-------+---------------------+
| a | foo | 2012-12-21 00:00:01 |
| b | foo | 2012-04-27 00:00:01 |
| c | bar | 2012-03-27 00:00:01 |
| d | bar | 2012-12-21 00:00:01 |
+---------+-------+---------------------+
4 rows in set (0.00 sec)
脚本输出:
$ ./pivot.sh
+------+------+------+------+---------------------+
| a | b | c | d | time |
+------+------+------+------+---------------------+
| NULL | NULL | bar | NULL | 2012-03-27 00:00:01 |
| NULL | foo | NULL | NULL | 2012-04-27 00:00:01 |
| foo | NULL | NULL | bar | 2012-12-21 00:00:01 |
+------+------+------+------+---------------------+
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