如何根据列内容前4个字母创建索引？

How can I create index on the basis of column content first 4 letter?

如何根据列内容前4个字母创建索引？

For example I have a table having multiple fields, one field is having name country, all Country name is in that table.

例如，我有一个包含多个字段的表，一个字段具有名称国家/地区，所有国家/地区名称都在该表中。

RANK    COUNTRY
--------------------------
1       Qatar
2       Luxembourg
3       Singapore
4       Brunei Darussalam
5       Kuwait
6       Norway
7       United Arab Emirates
8       Switzerland
9       United States
10      * SAR

Now I want to do the indexing on Country field. But I want the indexing on first 4 letter of that filed data.

现在我想在Country字段上进行索引。但我希望对该提交数据的前4个字母进行索引。

1 个解决方案

#1

This is called a "prefix" index:

这称为“前缀”索引：

INDEX(country(4))

But I don't recommend it. There are under 300 countries in this world; you may as well index the full strings.

但我不推荐它。这个世界上有不到300个国家;你也可以索引完整的字符串。