Detailed introduction to Oracle date format conversion

Oracle is a very popular relational database management system that supports a variety of date and time formats to meet various needs. Date format conversion is a very common operation when performing data processing, statistics and analysis. This article will introduce the relevant knowledge of Oracle date format conversion.

1. Oracle Date Data Type

In Oracle, date data types include DATE and TIMESTAMP. The DATE type stores date and time information, accurate to the second level; the TIMESTAMP type can store more precise time information, with an accuracy as high as nanosecond level.

2. Oracle date format

In Oracle, the date format consists of a series of format templates, using some predefined characters to represent different date and time elements. The following are some commonly used date format templates:

• YYYY: four-digit year
• YY: two-digit year
• MM: month (01~12)
• DD: Day of the month (01~31)
• HH: Hour (00~23)
• MI: Minute (00~59)
• SS: Seconds (00~59)

3. Oracle date formatting function

In Oracle, there are some date formatting functions that can Converts a date type to a string type, or converts a string type to a date type. The following are some commonly used date formatting functions:

• TO_CHAR(date,format): Convert date type to string type, format is format.
• TO_DATE(string,format): Convert string type to date type, format is format.

The following are some examples:

• TO_CHAR(SYSDATE,'YYYY-MM-DD'): Convert the current date (SYSDATE) to a string type, the format is "year month day".
• TO_DATE('2021-05-01','YYYY-MM-DD'): Convert the string type "2021-05-01" to a date type.

4. Oracle date calculation functions

In Oracle, there are also some date calculation functions that can add, subtract, compare and other operations on dates. The following are some commonly used date calculation functions:

• ADD_MONTHS(date,n): Add n months to the date.
• MONTHS_BETWEEN(date1,date2): Calculate the number of months between two dates.
• ROUND(date,fmt): Round the date according to the specified format (fmt).
• TRUNC(date,fmt): Truncate the date according to the specified format (fmt).

Here are some examples:

• ADD_MONTHS(SYSDATE,1): Add one month to the current date.
• MONTHS_BETWEEN('2021-05-01','2022-05-01'): Calculate the number of months between "2021-05-01" and "2022-05-01".
• ROUND(SYSDATE,'MONTH'): Round the current date into months.
• TRUNC(SYSDATE,'DD'): Truncate the current date by day.

5. Oracle date format conversion examples

The following are some examples of Oracle date format conversion:

• Convert the date type to String type:

SELECT TO_CHAR(SYSDATE,'YYYY-MM-DD HH24:MI:SS') FROM DUAL;

The output result is: "2022-01-01 15:23:45"

• Convert string type to date type:

SELECT TO_DATE('2022-01-01','YYYY-MM-DD ') FROM DUAL;

The output result is: "01-JAN-22"

• Calculate the number of hours difference between the current time and a certain date:

SELECT (SYSDATE - TO_DATE('2022-01-01','YYYY-MM-DD'))*24 FROM DUAL;

The output result is: "340.544444444444444444444444444"

• Truncate the current date by day:

SELECT TRUNC(SYSDATE,'DD') FROM DUAL;

The output result is: "01-JAN-22"

• Add 1 month to the current date:

SELECT ADD_MONTHS(SYSDATE,1) FROM DUAL;

The output result is: "01-FEB-22 "

6. Conclusion

This article introduces the knowledge related to Oracle date format conversion, including date data type, date format, date formatting function, date calculation function and related examples . Mastering this knowledge can make date-related data processing in Oracle database easier and more convenient.

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