合并两个表并在mysql中填入缺失值

Question

我在MySQL中有以下两个表：

表1：

ID Val1
1  100
2  200
3  300

表2：

ID Val2
2  50

如何将它们组合成这样的表？

ID Val1 Val2
1  100  0
2  200  50
3  300  0

Answer 1

SELECT Table1.ID, Table1.Val1, COALESCE(Table2.Val2, 0) AS Val2
FROM Table1 LEFT OUTER JOIN Table2 USING (ID)

Answer 2

将LEFT JOIN与IFNULL()结合使用，为Val2填写零

SELECT 
  Table1.ID,
  Table1.Val1,
  IFNULL(Table2.Val2, 0) AS Val2
FROM Table1 LEFT JOIN Table2 ON Table1.ID = Table2.ID

Answer 3

SELECT Table1.ID, Table1.Val1, COALESCE(Table2.Val2, 0) AS Val2
FROM Table1 LEFT OUTER JOIN Table2 USING (ID)
INTO NewTable