oracle常用函数：TO_CHAR

Convert Datatype To String	TO_CHAR(, ) RETURN VARCHAR2
	SELECT TO_CHAR(SYSDATE, 'MM/DD/YYYY HH:MI:SS') FROM dual;
Converts  DATE and  TIMESTAMP to VARCHAR2  with the specified format	TO_DATE(, , )
	SELECT TO_CHAR(datecol1, 'DAY-MONTH-YY') COL1,        TO_CHAR(datecol2, 'D-MM/YYYY HH24:MI:SS') COL2,        TO_CHAR(datecol2, 'YYYY-MON-DD HH24') COL3 FROM t;
Demo of FM Formatting From Tom Kyte (Oracle Magazine 3-4/2004)	SELECT TO_CHAR(dt, 'HH:MI AM') A,        TO_CHAR(dt, 'FMHH:MI AM') B,        TO_CHAR(dt, 'FMHHFM:MI AM') C FROM (SELECT TO_DATE('09:01 am', 'HH:MI AM') dt FROM dual);
Convert NUMBER to CHARACTER	TO_CHAR(number)
	SELECT TO_CHAR(123) FROM dual;
Convert NUMBER to HEX	TO_CHAR(NUMBER) RETURN HEX
	SELECT TO_CHAR(1048576,'XXXXXXXX') FROM dual;