draaitabel in mysql

Je kunt altijd een shellscript maken dat precies dat doet :-)

#!/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

Gegevens:

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)

Scriptuitvoer:

$ ./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 |
+------+------+------+------+---------------------+