combinate.md

# 组合索引

Goods 表结构如下：

```sql
create table goods(
    id int primary key auto_increment,
    category_id int,
    category varchar(64),
    name varchar(256),
    price decimal(12, 4),
    stock int,
    upper_time timestamp
)
```

现有大量查询 `select id, category_id, name, price, stock from goods where stock=? and category_id=? and name like ?`，
Joe 应该如何优化？

<hr/>

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* `show databases;` 列出所有数据库
* `show tables;` 列出所有表

## 答案

```sql
alter table goods add index (stock, category_id, name);
```

## 选项

### A

```sql
alter table goods add index (stock and category_id and name);
```

### B

```sql
alter table goods add index (concat(stock, category_id, name));
```

### C

```sql
alter table goods add index (stock + category_id + name);
```