To enter the time portion of a date, use the TO_DATE function with a format mask indicating the time portion, as in In a time-only entry, the date portion defaults to the first day of the current month. (midnight) if no time portion is entered. By default, the time in a date field is 00:00:00 A.M. Oracle stores time in 24-hour format - HH:MI:SS. If you want to indicate years in any century other than the 20th century, use a different format mask, as shown above. If you use the standard date format DD-MON-YY, YY gives the year in the 20th century (for example, 31-DEC-92 is December 31, 1992). To enter dates that are not in standard Oracle date format, use the TO_DATE function with a format mask: You can also change it during a user session with the ALTER SESSION statement. You can change this default date format for an instance with the parameter NLS_DATE_FORMAT. Date data is stored in fixed-length fields of seven bytes each, corresponding to century, year, month, day, hour, minute, and second.įor input and output of dates, the standard Oracle default date format is DD-MON-YY, as below: Oracle uses its own internal format to store dates. Unless BCE ('BC' in the format mask) is specifically used, CE date entries are the default. Oracle can store dates in the Julian era, ranging from JanuBCE through DecemCE (Common Era). The DATE datatype stores the year (including the century), the month, the day, the hours, the minutes, and the seconds (after midnight). The DATE datatype stores point-in-time values (dates and times) in a table. Zero and positive and negative infinity (only generated on import from Version 5 Oracle databases) are stored using unique representations: zero and negative infinity each require one byte positive infinity requires two bytes. + 1 byte (only for a negative number where the number of Taking this into account, the column data size for a particular numeric data value NUMBER ( p), where p is the precision of a given value (scale has no effect), can be calculated using the following formula: For example, the number 412 is stored in a format similar to 4.12 x 10^2, with one byte used to store the exponent (2) and two bytes used to store the three significant digits of the mantissa (4, 1, 2). (The resulting value is limited to 38 digits of precision.) Oracle does not store leading and trailing zeros. Each value is stored in scientific notation, with one byte used to store the exponent and up to 20 bytes to store the mantissa. Oracle stores numeric data in variable-length format. To enter numbers that do not use the current default decimal character, use the TO_NUMBER function. You can also change it for the duration of a session with the ALTER SESSION statement. (The decimal is the character that separates the integer and decimal parts of a number.) You can change the default decimal character with the initialization parameter NLS_NUMERIC_CHARACTERS. For example, specifying (7,-2) means Oracle should round to the nearest hundredths, as shown in Table 10-1.įor input and output of numbers, the standard Oracle default decimal character is a period, as in the number "1234.56". If you specify a negative scale, Oracle rounds the actual data to the specified number of places to the left of the decimal point. Table 10-1 How Scale Factors Affect Numeric Data Storage Input Data Table 10-1 shows examples of how data would be stored using different scale factors. When you specify numeric fields, it is a good idea to specify the precision and scale this provides extra integrity checking on input. In this case, the precision is 38 and the specified scale is maintained. You can specify a scale and no precision: Oracle guarantees portability of numbers with a precision equal to or less than 38 digits. If no scale is specified, the scale is zero. If a precision is not specified, the column stores values as given. Optionally, you can also specify a precision (total number of digits) and scale (number of digits to the right of the decimal point):
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