使用SQLite进行消费跟踪
我试图查询sqlite,它给出了电能表的消耗量。如果我想创建一个简单的示例:使用SQLite进行消费跟踪,sql,sqlite,consumption,Sql,Sqlite,Consumption,我试图查询sqlite,它给出了电能表的消耗量。如果我想创建一个简单的示例: CREATE TABLE datalog ( id INTEGER PRIMARY KEY AUTOINCREMENT, tstamp DATETIME DEFAULT CURRENT_TIMESTAMP, rValue REAL); INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 00:00:01', 25.1); INSERT INTO da
CREATE TABLE datalog (
id INTEGER PRIMARY KEY AUTOINCREMENT,
tstamp DATETIME DEFAULT CURRENT_TIMESTAMP,
rValue REAL);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 00:00:01', 25.1);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 00:15:01', 26.2);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 00:30:01', 27.5);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 00:45:01', 28.8);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 01:00:01', 29.4);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 01:15:01', 30.2);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 01:30:01', 31.5);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 01:45:01', 32.2);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 02:00:01', 33.9);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 02:15:01', 35.2);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 02:30:01', 36.1);
INSERT INTO datalog (tstamp,rValue) VALUES ('2020-01-02 15:30:01', 80.4);
我想为该表编写一个查询,通过选择今天的第一个读取值和日期时间(如果我们假设它是2020-01-02,则为今天)和今天的最后一个读取值和日期时间,给出电表的消耗量,并给出下表
startDT | startValue | lastDT | lastValue | consumption
2020-01-02 00:00:01 | 25.1 | 2020-01-02 15:30:01 | 80.4 | 55.3
没关系,我通过做更多的研究解决了这个问题 答案是在FROM子句中使用多个子查询
SELECT
startData.tstamp AS 'starttime',
startData.rValue AS 'startvalue',
lastData.tstamp AS 'lasttime',
lastData.rValue AS 'lastvalue',
(lastData.rValue-startData.rValue) AS 'consumption'
FROM ( SELECT tstamp, rValue
FROM datalog
WHERE tstamp>= datetime('now','start of day')
ORDER BY tstamp ASC LIMIT 1) startData,
( SELECT tstamp,rValue
FROM datalog
WHERE tstamp>= datetime('now','start of day')
ORDER BY tstamp DESC LIMIT 1) lastData;
无需交叉连接2个子查询。
您可以使用窗口功能执行此操作:
SELECT DISTINCT
MIN(tstamp) OVER () startDT,
FIRST_VALUE(rValue) OVER (ORDER BY tstamp) startValue,
MAX(tstamp) OVER () lastDT,
FIRST_VALUE(rValue) OVER (ORDER BY tstamp DESC) lastValue,
FIRST_VALUE(rValue) OVER (ORDER BY tstamp DESC) - FIRST_VALUE(rValue) OVER (ORDER BY tstamp) consumption
FROM datalog
WHERE date(tstamp) = CURRENT_DATE