mysql将常量作为临时表

MySQL中可以使用常量作为临时表，具体方法是在查询中使用SELECT语句定义常量表，例如：

SELECT 'apple' AS fruit, 2 AS quantity
UNION
SELECT 'banana' AS fruit, 3 AS quantity
UNION
SELECT 'orange' AS fruit, 1 AS quantity;

这个语句会创建一个临时表，包含三行数据，每行都包含一个水果名称和对应的数量。这个临时表可以在查询中使用，例如：

SELECT fruit, quantity FROM (
    SELECT 'apple' AS fruit, 2 AS quantity
    UNION
    SELECT 'banana' AS fruit, 3 AS quantity
    UNION
    SELECT 'orange' AS fruit, 1 AS quantity
) AS temp
WHERE quantity > 2;

这个查询会返回数量大于2的水果名称和对应的数量，即：

+--------+----------+
| fruit  | quantity |
+--------+----------+
| banana |        3 |
+--------+----------+