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The two column types used in the president table are VARCHAR and DATE.VARCHAR(n) means the column contains variable-length character (string) values, with a maximum length of n characters each. You choose the value of n according to how long you expect your values to be. state is declared as VARCHAR(2); that's all we need if states are entered using their two-character abbreviations. The other string-valued columns need to be wider to accommodate longer values.
The other column type we've used is DATE. This type indicates, not surprisingly, that the column holds date values. However, what may be surprising to you is the format in which dates are represented. MySQL expects dates to be specified in 'CCYY-MM-DD' format, where CC, YY, MM, and DD represent the century, year within the century, month, and date. This is the ANSI SQL standard for date representation (also known as ISO 8601 format). For example, a date of July 18, 2002 is specified in MySQL as '2002-07-18', not as '07-18-2002' or '18-07-2002'.
The only attributes we're using for the columns in the president table are NULL (values can be missing) and NOT NULL (values must be filled in). Most columns are NOT NULL because we'll always have a value for them. The two columns that can have NULL values are suffix (most names don't have one) and death (some presidents are still alive, so there is no date of death).
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