Question

因此，我编写的查询与this answer中描述的查询几乎相同。但是，我收到一条错误消息，指出：没有这样的列b.when。

我的选择语句：

SELECT
    mileage,
    (SELECT b.mileage FROM MileageEvents as b WHERE `b.when` < `a.when` ORDER BY `b.when` DESC LIMIT 1) as last_mileage,
    gallons,
    cost_per_gallon,
    `when`
FROM MileageEvents as a

我知道我以前已经写过这样的查询，但是我似乎无法弄清楚此查询的情况。我在做什么错了？

我的数据库转储：

PRAGMA foreign_keys=OFF;
BEGIN TRANSACTION;
CREATE TABLE IF NOT EXISTS "MileageEvents" (
    "mileage"   INTEGER,
    "when"  TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    "cost_per_gallon"   INTEGER,
    "gallons"   INTEGER,
    "id"    INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
    "car_id"    INTEGER NOT NULL
);
INSERT INTO MileageEvents VALUES(150000,'2019-03-12',3.3500000000000000888,12,1,1);
INSERT INTO MileageEvents VALUES(150300,'2019-03-19',3.25,12,2,1);
INSERT INTO MileageEvents VALUES(150693,'2019-03-22',3.4500000000000001776,12,3,1);
INSERT INTO MileageEvents VALUES(151000,'2019-03-25',3.3900000000000001243,12,4,1);
INSERT INTO MileageEvents VALUES(151600,'2019-04-01',2.25,12,5,1);
INSERT INTO MileageEvents VALUES(151883,'2019-06-10 23:01:43',2.4500000000000001776,11.695999999999999729,6,1);
DELETE FROM sqlite_sequence;
INSERT INTO sqlite_sequence VALUES('MileageEvents',6);
COMMIT;

Answer 1

（首先，我将使用普通的双引号转义而不是MySQL样式的反引号，或者更好的是，该标识符不是保留关键字）

您需要使用b."when"。您正在执行的操作将整个字符串b.when视为标识符，而表名和列名之间没有分隔。

重写：

SELECT
    mileage,
    (SELECT b.mileage FROM MileageEvents as b WHERE b."when" < a."when" ORDER BY b."when" DESC LIMIT 1) as last_mileage,
    gallons,
    cost_per_gallon,
    "when"
FROM MileageEvents as a;

注意：如果使用sqlite 3.25或更高版本，则可以完全避免子查询：

SELECT
    mileage,
    lag(mileage) OVER (ORDER BY "when") AS last_mileage,
    gallons,
    cost_per_gallon,
    "when"
FROM MileageEvents;

相关子查询中没有这样的列

1 个答案: