有兩種方式：
第一種是直接列出所有需要的查詢項
Select K1.ID,Keyword,Content1,Content2,Content3,Content4 From K1 Left Join K2 On K1.ID=K2.ID Left Join K3 on K1.ID=K3.ID Where K1.ID=你要查的ID
第二種是將K2和K3表組合，將兩表的四欄位組合成2個欄位
Select K1.ID,Keyword,Content_A,Content_B from K1 Inner Join (
Select ID,Content1 as Content_A,Content2 as Content_B From K2 union all
Select ID,Content3 as Content_A,Content4 as Content_B From K3) T on K1.ID=T.ID Where K1.ID=你要查的ID
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