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https://i.stack.imgur.com/5Pw2L.pngMySQL將行數倍增至列
我有一個問題,我想在MySQL中進行預處理。我有一個select返回一個id的多個行和列。我想將行轉換爲相同id的列,按照附圖對它們進行分組。列名對我來說並不重要,因爲我只需要每個id的值。
+---+---+---+---+-----+---+
| 1 | a | b | c | ... | x |
+---+---+---+---+-----+---+
| 1 | d | e | f | ... | y |
+---+---+---+---+-----+---+
| 2 | g | h | i | ... | z |
+---+---+---+---+-----+---+
| 2 | j | k | l | ... | q |
+---+---+---+---+-----+---+
| 3 | m | n | o | ... | w |
+---+---+---+---+-----+---+
| 3 | p | q | r | ... | t |
+---+---+---+---+-----+---+
+---+---+---+---+-----+---+---+---+---+-----+---+
| 1 | a | b | c | ... | x | d | e | f | ... | y |
+---+---+---+---+-----+---+---+---+---+-----+---+
| 2 | g | h | i | ... | z | j | k | l | ... | q |
+---+---+---+---+-----+---+---+---+---+-----+---+
| 3 | m | n | o | ... | w | p | q | r | ... | t |
+---+---+---+---+-----+---+---+---+---+-----+---+
如果MySQL是不是一個攔截器,你應該能夠得到使用PostgreSQL – FrankerZ
此功能這種轉變稱爲旋轉並一直問並在SO上多次回答。鏈接的重複主題解釋了靜態和動態主題。在這種情況下,您可能需要使用min或max作爲聚合函數而不是計數。請注意,在應用程序代碼中執行這種轉換可能比在sql中更高效。 – Shadow