Oracle 19c SQL

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  5. 2.2 DUAL Table

2.2 DUAL Table

  • DUAL is a table automatically created by Oracle Database along with the data dictionary.
  • DUAL is in the schema of the user SYS but is accessible by the name DUAL to all users.
  • It has one column, “DUMMY”, defined as VARCHAR2(1), and contains one row with a value “X”. Selecting from the DUAL table is useful for computing a constant expression with the SELECT statement.
SELECT 1 + 2 as res FROM DUAL;
SELECT 2*2/2 + 2*2 - 2 as res FROM DUAL;
SELECT 2*2/(2+2)*2 - 2 as res FROM DUAL;
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