dual in SQL

DUAL in SQL

DUAL:-DUAL is dummy table in Oracle .Owner of dual table is SYS user. 
                This table is used for calculation purpose.

SQL>SELECT * FROM DUAL;
SQL>DESC DUAL;
SQL>SELECT TABLE_NAME,OWNER FROM ALL_TABLES WHERE       TABLE_NAME='DUAL';

Examples:-

SQL>SELECT 2+5 FROM DUAL;

SQL>SELECT SYSDATE FROM DUAL;

SQL>SELECT USER FROM DUAL;

SQL>SELECT 1,2,3,4 FROM DUAL;

SQL>SELECT (SELECT COUNT(*) FROM EMP)+(SELECT COUNT(*) FROM DEPT) TOTAL FROM DUAL;

SQL>SELECT SQRT(144) FROM DUAL;

SQL>SELECT POWER(3,4) FROM DUAL;

SQL>SELECT EXP(3) FROM DUAL;--exponential e*e*e (e=2.718)

SQL>SELECT MOD(17,3) FROM DUAL;

SQL>SELECT ROUND(12.345678,2) FROM DUAL;

SQL>SELECT TRUNC(12.34567,2) FROM DUAL;

SQL>SELECT FLOOR(12.345678) FROM DUAL;

SQL>SELECT CEIL(12.345678) FROM DUAL;

SQL>SELECT 2*6 FROM DUAL;

SQL>SELECT 2*(13-9) FROM DUAL;

SQL>SELECT TRUNC(13.2365,2) FROM DUAL;

SQL>SELECT ROUND(13.2365,2) FROM DUAL;

SQL>SELECT CEIL(13.5674) FROM DUAL;

SQL>SELECT FLOOR(13.5674) FROM DUAL;

SQL>SELECT POWER(3,4) FROM DUAL;

SQL>SELECT SQRT(81) FROM DUAL;