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Julian Day Numbers

There is a simpler way to measure the passage of days. Based on a date that Joseph Scaliger suggested in 1583, astronomers use a continuous count of days since a fixed start point that is well before recorded history. Now, because many documentation sources (including most vendors' manuals) have this detail wrong, we're going to use a bit of emphasis here:

Julian Day 0 is the same as January 1 4713 B.C. on the proleptic Julian calendar.

In most DBMSs, there is a function for getting the Julian Day Number given a DATE value. Unfortunately, for a few DBMSs, there is a tendency to use the word Julian when giving the ordinal day number within a year—for example, they say that any January 1 date is Julian Day 1.

Naturally, different DBMSs return different values for a Julian-day function, depending on the way that they handle the Julian/Gregorian switch.

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