oracle conversion time format

In Oracle database, the timestamp data type can represent any date and time. However, its default format may not meet our needs, so time format conversion is required. This article will introduce how to use conversion functions to implement time format conversion in Oracle database.

1. TO_CHAR function

The TO_CHAR function can format a date type column or value into a specified string format. Among them, the first parameter is a value or column of date type, and the second parameter is a character expression in the date/time format to be converted. Commonly used date/time formats include the following:

• YYYY four-digit year, for example: 2022.
• MM Two-digit month, padded with leading zeros, for example: 04.
• DD Two-digit date, padded with leading zeros, for example: 30.
• hh Two-digit hour, padded with leading zeros, for example: 08.
• mi Two-digit minute, padded with leading zeros, for example: 45.
• ss Two-digit number of seconds, padded with leading zeros, for example: 12.

For example, to format the current time into the format of "YYYY-MM-DD hh:mi:ss", you can use the following SQL statement:

SELECT TO_CHAR(SYSDATE, 'YYYY-MM-DD hh24:mi:ss') FROM DUAL;

Among them, SYSDATE is The current system time, DUAL is an Oracle predefined table, which contains only one row and one column. It is often used to test single-column return value functions.

2. TO_DATE function

The TO_DATE function can convert a character expression into a date type value. Among them, the first parameter is the string to be converted, and the second parameter is the character expression in the date/time format of the string. Commonly used date/time formats are consistent with those in the TO_CHAR function.

For example, to convert the string "2022-04-30 08:45:12" into a DATE type value, you can use the following SQL statement:

SELECT TO_DATE('2022-04-30 08:45:12', 'YYYY-MM-DD hh24:mi:ss') FROM DUAL;

3. CAST function

The CAST function can convert one data type to another data type, including date/time type conversion. For example, to convert a DATE type value to a TIMESTAMP type, you can use the following SQL statement:

SELECT CAST(SYSDATE AS TIMESTAMP) FROM DUAL;

4. EXTRACT function

The EXTRACT function can convert a date/time type value from Extract specified parts, such as year, month, day, hour, minute, second, etc. Among them, the first parameter is the extracted part, and the second parameter is a date/time type value.

For example, to extract the year and month from the current time, you can use the following SQL statement:

SELECT EXTRACT(YEAR FROM SYSDATE), EXTRACT(MONTH FROM SYSDATE) FROM DUAL;

The above are several common methods and functions for time format conversion in Oracle database, different Scenarios may require the use of different methods and functions for conversion, which need to be selected based on actual needs.

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