获取两个表中的最小值

Question

我试图从两个表中获取最小值（一个返回值）。

下面的MySQL结构+数据：

table_master

`ID` (Unique) | `Amount` 

1 | 5.8 
2 | 22.1 
3 | 44.22 

---

table_variants

`table_master_ID` | `Amount` 

1 | 4.11 
1 | 5.12 
1 | 
1 | 
2 | 9.22 
3 | 

---

与此查询：

SELECT table_master.Amount, table_variants.Amount 
FROM table_master 
LEFT JOIN table_variants ON table_master.ID = table_variants.table_master_ID 
WHERE table_master.ID = 1 

我得到的是这样的：

5.8 | 4.11 
5.8 | 
5.8 | 5.12 
... 

现在我需要两个表的MIN Amount值。 ID的table_master是唯一的，table_variants中的数据是可选的。

我该怎么做？我试图MIN()与CASE()但没有成功。

任何提示？

TIA！

Answer 1

SELECT MIN(t.Amount) FROM 
(SELECT Amount FROM table_master WHERE ID = 1 
UNION SELECT Amount FROM table_variants WHERE table_master_ID = 1) AS t 

MySQL UNION Syntax

SELECT MIN(LEAST(table_master.Amount, table_variants.Amount)) 
FROM table_master 
LEFT JOIN table_variants ON table_master.ID = table_variants.table_master_ID 
WHERE table_master.ID = 1 

MySQL LEAST Function

Answer 2

尝试

SELECT MIN(CASE WHEN table_master.Amount<= table_variants.Amount AND table_variants.Amount IS NULL THEN table_master.Amount ELSE table_variants.Amount END) 
FROM table_master 
LEFT JOIN table_variants ON table_master.ID = table_variants.table_master_ID 
WHERE table_master.ID = 1 

This shows how it works

Answer 3

您可以使用UNION到chieve这样的：

SELECT "min from table1", MIN(Amount) FROM table_master 
UNION 
SELECT "min from table2", MIN(Amount) FROM table_variants 

Answer 4

试试这个 -

SELECT LEAST(MIN(a.amount), MIN(b.value)) 
FROM table_master a, table_variants b 
WHERE a.id = b.table_master_ID 
AND a.id = 1;