Oracle SQL Developer

Using Pseudocolumns, Sequences, and SQL Functions6.5 Using Pseudocolumns, Sequences, and SQL FunctionsWith SQL built-in functions you can manipulate character, numeric, and date data inSQL statements. You can also perform operations on a collection of data with theaggregate functions.Pseudocolumns are built-in values that provide specific information with a query andare similar to functions without arguments. However, functions without argumentstypically return the same value for every row in the result set, whereaspseudocolumns typically return a different value for each row.This topic includes the following topics:■ Using Pseudocolumns With SQL■ Using Sequences■ Using Character Functions■ Using Arithmetic Operators■ Using Numeric Functions■ Using Date Functions■ Using Aggregate FunctionsSee Also:■Oracle Database SQL Reference for detailed information on SQLfunctions.6.5.1 Using Pseudocolumns With SQLA pseudocolumns is similar to a table column, but is not actually stored in a table. Apseudocolumn returns a value so it is similar to a function without argument. OracleDatabase provides several pseudocolumns, such as the ROWNUM, SYSDATE, and USER.The ROWNUM pseudocolumn returns a number indicating the order in which Oracleselects the row in a query. SYSDATE returns the current date and time set for theoperating system on which the database resides. USER returns the name of the username that is currently logged in.Example 6–13 show the use of the ROWNUM, SYSDATE, and USER pseudocolumns. Notethe use of the table DUAL, which is automatically created by Oracle Database for use asa dummy table in SQL statements.Example 6–13 Using Pseudocolumns-- the following statement displays the SYSDATE, which is the current system date-- NOW is a column alias for display purposes-- DUAL is a dummy table with one row simply used to complete the SELECT statementSELECT SYSDATE "NOW" FROM DUAL;-- display the name of the current user, the user name should be HRSELECT USER FROM DUAL;-- using ROWNUM < 10 limits the number of rows returned to less than 10SELECT employee_id, hire_date, SYSDATE FROM employees WHERE ROWNUM < 10;See Example 6–18 on page 6-14 for another example of the use of SYSDATE.6-10 SQL Developer Online Help