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SQL VISUAL QUICKSTART GUIDE- P11

SQL VISUAL QUICKSTART GUIDE- P11:SQL (pronounced es-kyoo-el) is the standard programming language for creating, updating, and retrieving information that is stored in databases. With SQL, you can turn your ordinary questions (“Where do our customers live?”) into statements that your database system can understand (SELECT DISTINCT city, state FROM customers;) | Chapter 3 Interval Types Interval Types DBMS conformance to standard DBMS cnT r m SQL interval types is spotty or nonexistent so you might not find this section to be useful in practice. DBMSs have their own extended data types and functions that calculate intervals and perform date and time arithmetic. Use interval data types to represent sets of time values or spans of time. An interval value has these characteristics It stores the quantity of time between two datetime values. Between 09 00 and 13 30 is an interval of 04 30 4 hours and 30 minutes for example. If you subtract two datetime values you get an interval. It can be used to increment or decrement a datetime value see Performing Datetime and Interval Arithmetic in Chapter 5. It has the same fields as datetime values YEAR HOUR SECOND and so on but the number can have a forward or - backward sign to indicate a direction in time. The field separators are the same as for datetime values. It comes in two categories year-month intervals and day-time intervals. A year-month interval expresses an interval as years and a whole number of months. A day-time interval expresses an interval as days hours minutes and seconds. It has a single-field or multiple-field qualifier. A single-field qualifier is specified as YEAR MONTH DAY HOUR MINUTE or SECOND. A multiple-field qualifier is specified as start_field TO end_field start_field is YEAR DAY HOUR or MINUTE and end_field is YEAR MONTH DAY HOUR MINUTE or SECOND. end__field must be a smaller time period than start_field. A single-field column defined as INTERVAL HOUR could store intervals such as 4 hours or 25 hours for example. A multiplefield column defined as INTERVAL DAY TO MINUTE could store intervals such as 2 days 5 hours 10 minutes for example. Table 3.16 Interval Types Type Description Year-month These intervals contain only a year value only a month value or both. The valid column types are INTERVAL YEAR INTERVAL YEAR precision INTERVAL MONTH INTERVAL MONTH .