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问题：执行计划
通过执行计划检查你对 MySQL 如何评估和比较查询性能的理解。
表
| 字段 | 类型 |
|---|---|
| ProductID | INT |
| ProductName | VARCHAR(50) |
| CategoryID | INT |
| Price | DECIMAL(10,2) |
| Stock | INT |
| LastRestockDate | DATE |
表
| 字段 | 类型 |
|---|---|
| OrderDetailID | INT |
| OrderID | INT |
| ProductID | INT |
| Quantity | INT |
| TotalItemPrice | DECIMAL(10,2) |
表
| EXPLAIN |
|---|
| -> Nested loop semijoin (cost=12 rows=26) (actual time=0.0459..0.115 rows=21 loops=1)\n -> Covering index scan on p using ProductName (cost=2.85 rows=26) (actual time=0.0179..0.0282 rows=26 loops=1)\n -> Covering index lookup on od using ProductID (ProductID=p.ProductID) (cost=0.254 rows=1) (actual time=0.0031..0.0031 rows=0.808 loops=26)\n |
表
| EXPLAIN |
|---|
| -> Table scan on (cost=14.7..17.4 rows=26) (actual time=0.169..0.172 rows=21 loops=1)\n -> Temporary table with deduplication (cost=14.6..14.6 rows=26) (actual time=0.168..0.168 rows=21 loops=1)\n -> Nested loop inner join (cost=12 rows=26) (actual time=0.0268..0.078 rows=21 loops=1)\n -> Covering index scan on p using ProductName (cost=2.85 rows=26) (actual time=0.0153..0.0226 rows=26 loops=1)\n -> Limit: 1 row(s) (cost=0.254 rows=1) (actual time=0.00187..0.00189 rows=0.808 loops=26)\n -> Covering index lookup on od using ProductID (ProductID=p.ProductID) (cost=0.254 rows=1) (actual time=0.00174..0.00174 rows=0.808 loops=26)\n |
1/*Write your queries below*/ 2-- Version A: EXISTS based plan 3 4 5-- Version B: JOIN based plan (distinct products that appear in Order_Details) 6 7 8-- Optional: Run each SELECT without EXPLAIN to confirm they return the same set of products
所需技能如下：
- 理解执行计划
- 能够使用
EXPLAIN和EXPLAIN ANALYZE检查查询 - 基本熟悉在计划中阅读索引使用和连接策略
所需技能如下：
- 理解执行计划
- 能够使用
EXPLAIN和EXPLAIN ANALYZE检查查询 - 基本熟悉在计划中阅读索引使用和连接策略
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