mySQL getting rank from score

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i have numbers from my table fields score, i want to \[code\]fill/add\[/code\] the rank field according to score like below. How i can do this? \[code\]Score --> Rank75 82 83 75 90 78 78 75 80 73 76 \[/code\]this make like this when we sort it out:\[code\]Score > Rank90 183 282 380 478 5.5078 5.5076 775 8.5075 8.5075 8.5073 11\[/code\]Rank is blank at first, then i update it, or create new field to fill in the rank