Question

我有一个类似的查询..它不起作用，但是，我在WHERE NOT EXISTS位上遇到语法错误。但是我不确定它会按照我想要它的方式工作。我想做的就是让它在任何一天只能有一个'B'，它将是第一个实例..但我不确定下面的代码是否有效，无论如何，任何事情都会是'B'。

UPDATE FoodIntake
 SET MealTypeCode = CASE

WHEN substr(DateTime, -8)
 BETWEEN (SELECT BreakfastStart FROM Patient WHERE PatientId = :PatientId)
 AND (SELECT LunchStart FROM Patient WHERE PatientId = :PatientId)
 AND CarbAmount >= 25
 AND MealTypeCode IS NULL
 WHERE NOT EXISTS (
    SELECT * FROM FoodIntake as Old 
    WHERE MealTypeCode = 'B' 
    AND substr(Old.DateTime, 10) = substr(FoodIntake.DateTime, 10)
)
 THEN 'B'
END

我不确定如何处理的另一个选项是标记应用为B的所有内容，然后执行第二个查询以查找一天中有2个B并且将第二个重命名为其他内容的任何时间

我有一个我试过的查询，但我知道它有一些重大问题..有一些语法错误我无法弄清楚，但我认为它至少可以解决我想做的事。

UPDATE FoodIntake
 SET MealTypeCode = 'U'
WHERE MealTypeCode = 'B'
AND count(SELECT 1 FROM FoodIntake as Old WHERE MealTypeCode ='B' AND substr(Old.DateTime, 10) = substr(FoodIntake.DateTime, 10) ) > 1
AND FoodIntake.DateTime > (SELECT DateTime FROM FoodIntake as Old WHERE MealTypeCode ='B' AND substr(Old.DateTime, 10) = substr(FoodIntake.DateTime, 10) ORDER By DateTime ASC LIMIT = count-1)

Answer 1

我认为你最好使用IF ... ELSE语句，虽然可能更详细一点，但更明确地说明了这里发生的逻辑。

IF (SELECT COUNT(1) FROM FoodIntake 
    WHERE (date('now') BETWEEN date('now','start of day') 
    AND date('now','start of day','+1 day') )
    AND MealTypeCode = 'B') > 0

 -- Make update based on 'B' code already taken

ELSE

 -- Make update based on 'B' code not yet taken

我不是一个SQLite人，但我对mySQL和T-SQL很好，所以如果日期函数不准确，我引用了这篇文章：http://www.sqlite.org/cvstrac/wiki?p=DateAndTimeFunctions

如何将事件类型限制为每天一个

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