order by coalesce
时间: 2024-06-19 10:03:17 浏览: 8
ORDER BY是SQL语句中用于指定查询结果排序方式的子句。而COALESCE函数可以返回参数列表中的第一个非空表达式的值。因此,ORDER BY COALESCE(column_name, value)语句可以将查询结果按照指定列(column_name)进行排序,如果该列为空,则以指定的值(value)进行排序。
举个例子,假设我们有一个表格存储用户信息,其中包括名字(name)和年龄(age)两个列。如果我们想按照年龄进行排序,但是有些用户没有填写年龄,此时我们可以使用ORDER BY COALESCE(age, 100),将年龄为空的用户的年龄赋值为100,然后再按照年龄排序。
相关问题
优化成mysql脚本,不使用full outer join;SELECT COALESCE(storage_in.in_date, storage_out.out_date) AS date, COALESCE(storage_in.product_name, storage_out.product_name) AS product_name, IFNULL(storage_in.quantity,0) AS IN_, IFNULL(storage_out.quantity,0) AS OUT_, SUM(IFNULL(storage_in.quantity,0) - IFNULL(storage_out.quantity,0)) OVER (PARTITION BY COALESCE(storage_in.in_date,storage_out.out_date), COALESCE(storage_in.product_name,storage_out.product_name) ORDER BY COALESCE(storage_in.in_date, storage_out.out_date)) AS END_ FROM storage_in FULL OUTER JOIN storage_out ON storage_in.product_name=storage_out.product_name AND storage_in.in_date = storage_out.out_date ORDER BY 1,2;
以下是将 FULL OUTER JOIN 转换为 MySQL 脚本的方法,使用 UNION 和 LEFT JOIN 和 RIGHT JOIN 组合:
```
SELECT COALESCE(storage_in.in_date, storage_out.out_date) AS date,
COALESCE(storage_in.product_name, storage_out.product_name) AS product_name,
IFNULL(storage_in.quantity, 0) AS IN_,
IFNULL(storage_out.quantity, 0) AS OUT_,
SUM(IFNULL(storage_in.quantity, 0) - IFNULL(storage_out.quantity, 0))
OVER (PARTITION BY COALESCE(storage_in.in_date, storage_out.out_date),
COALESCE(storage_in.product_name, storage_out.product_name)
ORDER BY COALESCE(storage_in.in_date, storage_out.out_date)) AS END_
FROM
(SELECT in_date, product_name, quantity FROM storage_in
UNION
SELECT out_date, product_name, 0 FROM storage_out) AS storage
LEFT JOIN storage_in ON storage.in_date = storage_in.in_date
AND storage.product_name = storage_in.product_name
LEFT JOIN storage_out ON storage.out_date = storage_out.out_date
AND storage.product_name = storage_out.product_name
ORDER BY 1, 2;
```
这个脚本使用 UNION 将 storage_in 和 storage_out 表中的数据组合起来,LEFT JOIN 和 RIGHT JOIN 分别连接 storage_in 和 storage_out 表,从而实现 FULL OUTER JOIN 的效果。
SELECT COALESCE(storage_in.in_date, storage_out.out_date) AS date, COALESCE(storage_in.product_name, storage_out.product_name) AS product_name, IFNULL(storage_in.quantity, 0) AS IN, IFNULL(storage_out.quantity, 0) AS OUT, SUM(IFNULL(storage_in.quantity, 0) - IFNULL(storage_out.quantity, 0)) OVER (PARTITION BY COALESCE(storage_in.in_date, storage_out.out_date), COALESCE(storage_in.product_name, storage_out.product_name) ORDER BY COALESCE(storage_in.in_date, storage_out.out_date)) AS END FROM storage_in FULL OUTER JOIN storage_out ON storage_in.product_name = storage_out.pproduct_name AND storage_in.in_date = storage_out.out_date ORDER BY 1,2;
这是一个 SQL 查询语句,用于从两个表中获取产品进出库存信息,并计算每个产品在每个日期的总库存。其中使用了 COALESCE 函数来处理空值,IFNULL 函数来处理 NULL 值。JOIN 条件是产品名称和日期相等,使用了 FULL OUTER JOIN 来保证左右两个表都包含在结果中。最后使用了 OVER 子句来计算每个产品在每个日期的总库存。