[英]MYSQL Multiple rows of same table to result in multiple columns depending on the criteria
結果是:我想獲取具有msr_name或'PRE'或'POST'或兩者均為的記錄
id | msr_name1(only pre) | msr_data1(only pre) | msr_name2(only post) | msr_data2(only post)
16703 PRE pre_data POST post_data
16711 PRE pre_data NULL NULL
16715 NULL NULL POST post_data
SELECT a.id AS id,
b.msr_name AS msr_name1, b.msr_data AS msr_data1,
c.msr_name AS msr_name2, c.msr_data AS msr_data2
FROM (SELECT DISTINCT id FROM Students WHERE msr_name IN ('PRE', 'POST')) AS a
LEFT JOIN Students AS b ON (a.id=b.id AND b.msr_name = 'PRE')
LEFT JOIN Students AS c ON (a.id=c.id AND c.msr_name = 'POST');
對我來說輸出是:
+-------+-----------+-----------+-----------+-----------+
| id | msr_name1 | msr_data1 | msr_name2 | msr_data2 |
+-------+-----------+-----------+-----------+-----------+
| 16703 | PRE | pre_data | POST | post_data |
| 16711 | PRE | pre_data | NULL | NULL |
| 16715 | NULL | NULL | POST | post_data |
+-------+-----------+-----------+-----------+-----------+
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