IF语句在SQL中的where子句中

Question

I'm developing a calendar app. It stores times in two formats. The table have following columns title, startDate, startTime . If the user provides start time plus start date. The database stores UNIX time stamp(number of seconds since UNIX epok) in the column startTime , while startDate is NULL . If the user only provide a start date, the database stores the date in format nnnn-mm-dd in startDate and NULL in ´startTime`. I have this DB structure, because it's easier to display times around the world, because different timezones have different daylight saving times.

I want select the events that are occurring after a specified date. The client computer provide the server with a UNIX timestamp of the beginning of that day( $unix ) and a date( $date ) in the format nnnn-mm-dd to select the correct dates.

The problem is, I don't know how to select those days that are occurring as specified above. This solution is not applicable for me, even though it works:

SELECT *
  FROM events
 WHERE startDate >= '$date'
   OR startTime >= '$unix'

The thing is I have in some rows where unix time stamp is provided in startTime , I also have a date provided in startDate and other reason I which I don't want to explain. And because of that I can't use the solution above.

I need some kind of solution that have an IF statement inside the Where clause like:

SELECT *
  FROM events
 WHERE IF(startTime = NULL, startDate >= '$date', startTime >= '$unix')

I'm just guessing this solution. But is it right?

Answer 1

WHERE (startTime IS NULL AND startDate >= '$date')
   OR (startTime IS NOT NULL AND startTime >= '$unix')

Answer 2

All SQL dialects support CASE WHEN:

SELECT *
 FROM events
WHERE CASE WHEN startTime is null
           THEN startDate >= '$date'
           ELSE startTime >= '$unix'

Answer 3

I know this is an old question but I think this is the best way to proceed...

SELECT *
FROM events
WHERE IF(startTime IS NULL, '$date', '$unix') =< startDate

Answer 4

You just need some combined boolean logic in the WHERE clause:

SELECT * 
FROM events
WHERE 
    (startDate IS NULL AND startTime >= '$unix') OR
    (startTime IS NULL AND startDate >= '$date')

Answer 5

SELECT * 
FROM events 
WHERE 
  (startDate >= '$date' OR startTime >= '$unix')
AND 
  startDate != NULL

This will not return any row that has null value for startDate

Answer 6

I'm assuming that you want to use startDate when startDate is not null, and startTime when startTime is not null... then try this...

SELECT * 
FROM events
WHERE (startTime is not NULL and startDate >= '$date') 
OR (startTime is not NULL and startTime >= '$unix')

You can use the CASE statement also, but this makes more sense is more readable.