Orcale date functions to_date () and to_char (), orcaleto_date

Orcale date functions to_date () and to_char (), orcaleto_date
The two functions of date conversion are to_date () and to_char (). The to_date () function converts the character type to the date type in a certain format, and to_char () convert a date to a certain format to a character type

When the time needs to be accurate, it is best to use to_char () to compare with character types. Comparison methods (=, >=, <=, between and) <,> need to be escaped, they are <>

To_date:

To_date ('1970-01-20 ', 'yyyy-mm-dd'). The former is a string, and the string date is converted to the date format specified by the input format template.

Note that when the converted date format includes time, minute, and second: to_date ('2017-01-20 12:34:56 ', 'yyyy-mm-dd hh24: mi: ss '), the template has HH, HH12 (in 12-hour format, the time range is: 0:00:00-23:59:59) HH24 :() in 24-hour format, the value is 0:00:00-23:59:59)

To_char:

To_char (dateType, 'yyyy-mm-dd hh24: mi: ss') converts the date dateType in the format of date to the year, month, and day of the character type.

Query the number of weeks for a given date:

Select to_char (to_date ('1970-01-20 ', 'yyyy-mm-dd'), 'day') from dual; // Saturday

Obtain the date seven days before the given time:

String createTime = "2018-01-20" Calendar before7day = Calendar. getInstance ();

Date date = null; try {

Date = new SimpleDateFormat ("yy-MM-dd"). parse (createTime );

Before7day. setTime (date );

Int day = before7day. get (Calendar. DATE );

Before7day. set (Calendar. DATE, day-7 );

String dayBefore = new SimpleDateFormat ("yyyy-MM-dd"). format (before7day. getTime ();} catch (ParseException e) {e. printStackTrace ();}