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The purpose of a PL/SQL function is generally used to compute and return a single value. This returned value may be a single scalar value (such as a number, date or character string) or a single collection (such as a nested table or array). User-defined functions supplement the built-in functions provided by Oracle Corporation. [6]
Reserved words in SQL and related products In SQL:2023 [3] In IBM Db2 13 [4] In Mimer SQL 11.0 [5] In MySQL 8.0 [6] In Oracle Database 23c [7] In PostgreSQL 16 [1] In Microsoft SQL Server 2022 [2]
System time is measured by a system clock, which is typically implemented as a simple count of the number of ticks that have transpired since some arbitrary starting date, called the epoch. For example, Unix and POSIX -compliant systems encode system time (" Unix time ") as the number of seconds elapsed since the start of the Unix epoch at 1 ...
Versions 9, [10] [11] 10g and 11g implement the time-sliced queries in what they call Flashback Queries, using the alternative syntax AS OF TIMESTAMP. [12] Notably both of Oracle's implementations depend on the database's rollback segment and so only allow temporal queries against recent changes which are still being retained for backup.
Many computer systems measure time and date using Unix time, an international standard for digital timekeeping.Unix time is defined as the number of seconds elapsed since 00:00:00 UTC on 1 January 1970 (an arbitrarily chosen time based on the creation of the first Unix system), which has been dubbed the Unix epoch.
A distinction is sometimes made between the terms datestamp, timestamp and date-timestamp: Datestamp or DS: A date, for example 2025-01-10 according to ISO 8601; Timestamp or TS: A time of day, for example 02:09:41 using 24-hour clock; Date-timestamp or DTS: Date and time, for example 2025-01-10, 02:09:41
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...
With the development of SQL and its attendant use in real-life applications, database users realized that when they added date columns to key fields, some issues arose. For example, if a table has a primary key and some attributes, adding a date to the primary key to track historical changes can lead to creation of more rows than intended.