and keywords in oracle notes

Some system functions, custom functions, and keywords in oracle notes the Inscription: Collect some oracle knowledge points commonly used in work, constantly update and accumulate, and use it as your own notepad. the some keywords the 1 IS NOT NULL, to determine whether the field is empty the [sql] select * from t_user u where u.name is not null the 2 CASE WHEN. ． ． THEN . ． ． ELSE. ． ． END , conditional statement [sql] SELECT CASE WHEN & #39; condition & #39; IS NOT NULL THEN & #39; condition is true & #39; ELSE & #39; condition is not true & #39; END AS result FROM t_user the 3 EXITS , NOT EXITS, judge whether it exists, usually put it behind WHERE the some system functions the 1. TO_CHAR() [sql] select to_char(sysdate,’yyyy-MM-dd HH24:mi:ss’) FROM DUAL Display: 2012-06-15 10:11:45 www.2cto.com 2. TO_DATE() Convert to a time in a certain format [sql] select to_date('$time parameter $0:0:0','yyyy-mm-dd hh24:mi:ss') from dual The time parameter can be: 2012-06-15 the some custom functions the 1. Write a function CHECK_DEMAND_IS_NOTICE that is used in work. This function needs to pass in a NUMBER type of data, and the result returns a VARCHAR2 type of…