在两个表格中选择数据

Question

表1：

+-----------+----------+------------+
| FirstName | LastName | Qty        |
+-----------+----------+------------+
| Tia       | Carrera  |  5         |
| Nikki     | Taylor   |  8         |
+-----------+----------+------------+

表2：

+-----------+----------+------------+
| FirstName | LastName | Qty        |
+-----------+----------+------------+
| Tia       | Carrera  | 5          |
| Nikki     | Taylor   | 8          |
| Yamila    | Diaz     | 30         |
+-----------+----------+------------+

表

中行的示例输出

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Answer 1

您应该使用与FirstName和LastName不同的列创建新列并定义PK和FK。但是使用当前结构，您可以使用LEFT JOIN和COALESCE：

SELECT t1.FirstName, t1.LastName, COALESCE(t2.Qty, t1.Qty) AS Qty
FROM table1 t1
LEFT JOIN table2 t2
  ON t1.FirstName = t2.FirstName
 AND t1.LastName = t2.LastName;

的 SqlFiddleDemo

输出：

╔════════════╦═══════════╦═════╗
║ FirstName  ║ LastName  ║ Qty ║
╠════════════╬═══════════╬═════╣
║ Nikki      ║ Taylor    ║   8 ║
║ Tia        ║ Carrera   ║   5 ║
║ Yamila     ║ Diaz      ║  30 ║
╚════════════╩═══════════╩═════╝

Answer 2

可能会有所帮助

SELECT * FROM Table2
UNION ALL
SELECT * FROM Table1
    WHERE FirstName NOT IN(SELECT FirstName FROM Table2) AND 
          LastName  NOT IN(SELECT LastName FROM Table2)