SQL 显示库存更新

Question

我有一个 table 显示库存的所有更新：

╔══════════════╦════════╦══════════╦═══════╗
║   ItemName   ║  Type  ║ Quantity ║ Date  ║
╠══════════════╬════════╬══════════╬═══════╣
║ BottledWater ║ Add    ║       50 ║ 07/03 ║
║ BottledWater ║ Deduct ║       20 ║ 07/03 ║
║ Chips        ║ Add    ║       30 ║ 07/02 ║
║ BottledWater ║ Deduct ║       10 ║ 07/02 ║
║ Chips        ║ Deduct ║       20 ║ 07/01 ║
╚══════════════╩════════╩══════════╩═══════╝

我想编写一个查询 return 一个 table 来显示添加和扣除库存的项目总数，table 看起来像：

╔══════════════╦═══════╦══════════╗
║   ItemName   ║ Added ║ Deducted ║
╠══════════════╬═══════╬══════════╣
║ BottledWater ║    50 ║       30 ║
║ Chips        ║    30 ║       20 ║
╚══════════════╩═══════╩══════════╝

有什么想法吗？

Answer 1

只使用条件聚合：

select item,
       sum(case when type = 'Add' then quantity else 0 end) as added,
       sum(case when type = 'Deduct' then quantity else 0 end) as deducted
from inventory
group by item;

Answer 2

语法略有偏差，但这是伪代码：

select ItemName, sum(Type==add) as added, sum(Type==deduct) as deducted, from inventory group by ItemName

SQL 显示库存更新

SQL Display Inventory Updates

sql

sql-server-ce