三張圖辨析所謂select *性能劣於select XXX

原創 烫烫烫口 2020-02-21 18:53

該場景主要適用於僅查詢索引字段的情況，否則其餘情況一概同等而論。但是大部分應用場景我們需要將幾乎所有字段讀取出來，所以select *和select xxx差別不大。

1、展示索引字段和非索引字段，全表掃描

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2、展示使用索引字段的情況，使用了主鍵索引

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3、select *情況，全表掃描
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