Numbers can be written as integers, decimal numbers, dates, times, or datetime values. They can also be included in scientific notations with an E preceding the power of ten. For example, these are all numbers:
注意：A single period by itself is considered a missing numeric value (sometimes called NaN for “not a number”).
For more information about dates, times, and date-time values, see “Date-Time Functions and Formats” on page 134 in the “Types of Data” chapter. See “Currency” on page 146 in the “Types of Data” chapter for details about combining numbers with currency symbols.