Varchar上的索引是否会产生性能差异? [英] Does index on Varchar make performance difference?
问题描述
varchar列上的索引是否会使查询运行得更慢?
我可以把它变成int。而且我不需要进行LIKE%比较。
Does index on a varchar column make the query run slower? I can make that be int. and I don't need to do the LIKE % comparison.
推荐答案
varchar列上的索引是否会使查询运行得更慢?
Does index on a varchar column make the query run slower?
不,它没有。
如果优化器决定使用索引,查询将运行得更快。 INSERT
s / UPDATE
s / DELETE
在该表上会慢一些,但不太可能注意到。
No, it does not.
If the optimizer decides to use of the index, the query will run faster. INSERT
s/UPDATE
s/DELETE
s on that table will be slower, but not likely enough to notice.
我不需要进行LIKE%比较
I don't need to do the LIKE % comparison
请注意使用:
LIKE '%whatever%'
... 不使用索引,但以下将:
...will not use an index, but the following will:
LIKE 'whatever%'
密钥是通配符串的左侧意味着不能使用列上的索引。
The key is wildcarding the lefthand side of the string means that an index on the column can't be used.
也知道 MySQL限制为索引留出的空间量 - 对于MyISAM(InnoDB为767字节)表,它们最长可达1000字节。
Also know that MySQL limits the amount of space set aside for indexes - they can be up to 1000 bytes long for MyISAM (767 bytes for InnoDB) tables.
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