Question

以下是我的表格：

CREATE TABLE Ships (name VARCHAR(20) PRIMARY KEY, launched DATE);
CREATE TABLE Battles (name VARCHAR(20) PRIMARY KEY, battledate DATE);

现在，当我尝试这样做时：

SELECT launched FROM Ships WHERE name='ship_one' > (SELECT battledate FROM Battles WHERE name='battle_one');

它触发了这个：

ERROR:  invalid input syntax for type date: "ship_one"

但名称应该是字符串，而不是日期。

SELECT launched FROM Ships WHERE name='ship_one';

工作正常

SELECT now() > (SELECT battledate FROM Battles WHERE name='battle_one');

也可以正常工作（输出f表示错误）

任何人都可以找出问题所在吗？

当我尝试

时

(SELECT launched FROM Ships WHERE name='ship_one') > (SELECT battledate FROM Battles WHERE name='battle_one');

它返回

syntax error at or near ">"

Answer 1

你是混合条件这是一个条件

SELECT launched FROM Ships WHERE name='ship_one'

这似乎是另一个条件。

> (SELECT battledate FROM Battles WHERE name='battle_one');

您正在尝试使用日期混合和布尔条件（name ='ship_one'，它返回一个布尔值）。

SELECT launched FROM Ships WHERE name='ship_one' **AND** somedate > (SELECT battledate FROM Battles WHERE name='battle_one');

Answer 2

搞定了

select (select launched from ships where name = 'ship_one') > (select battledate from battles where name = 'battle_one');

Answer 3

 WHERE name='ship_one' > (SELECT battledate FROM Battles WHERE name='battle_one');

缩减为：

 (boolean) > battledate                   (error)

可能想要：

where name='ship one' and something??? > battledate