Oracle: 索引与 … where upper(a) = XX

摘自《Troubleshooting Oracle Performance》

1.如果索引建在 a 列上,则

   … where upper(a) = XX 用不上索引

   … where a = upper(xx) 仍可以用得上索引

2.如果索引建在 upper(a) 这个函数上,或者实现了upper(a)的虚拟列上, 则

     … where upper(a) = XX 可以用得上索引

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