如何向 MySQL 表添加索引?

How do I add indexes to MySQL tables?(如何向 MySQL 表添加索引?)

问题描述

我有一个非常大的 MySQL 表，其中包含大约 150,000 行数据.目前，当我尝试运行

I've got a very large MySQL table with about 150,000 rows of data. Currently, when I try and run

SELECT * FROM table WHERE id = '1';

代码运行良好，因为 ID 字段是主索引.但是，对于项目的最新发展，我必须通过另一个字段搜索数据库.例如:

the code runs fine as the ID field is the primary index. However, for a recent development in the project, I have to search the database by another field. For example:

SELECT * FROM table WHERE product_id = '1';

此字段以前未编入索引；但是，我添加了一个，因此 mysql 现在对该字段进行索引，但是当我尝试运行上述查询时，它运行速度非常慢.EXPLAIN 查询显示，当我已经添加了 product_id 字段时，没有索引，因此查询需要 20 分钟到 30 分钟的任何时间来返回单行.

This field was not previously indexed; however, I've added one, so mysql now indexes the field, but when I try to run the above query, it runs very slowly. An EXPLAIN query reveals that there is no index for the product_id field when I've already added one, and as a result the query takes any where from 20 minutes to 30 minutes to return a single row.

我的完整解释结果是:

| id | select_type | table | type | possible_keys| key  | key_len | ref  | rows  | Extra       |
+----+-------------+-------+------+--------------+------+---------+------+-------+------------------+
|  1 | SIMPLE      | table | ALL  | NULL         | NULL | NULL    | NULL |157211 | Using where |
+----+-------------+-------+------+--------------+------+---------+------+-------+------------------+

注意到我刚刚看了一下，ID 字段存储为 INT 而 PRODUCT_ID 字段存储为 VARCHAR 可能会有所帮助.这可能是问题的根源吗?

It might be helpful to note that I've just taken a look, and ID field is stored as INT whereas the PRODUCT_ID field is stored as VARCHAR. Could this be the source of the problem?

推荐答案

ALTER TABLE `table` ADD INDEX `product_id_index` (`product_id`)

永远不要在 MySQL 中比较 integer 和 strings.如果 id 是 int，请删除引号.

Never compare integer to strings in MySQL. If id is int, remove the quotes.

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