What is the usage of to_char in Oracle?

The to_char function in Oracle is used to convert data types such as numbers, dates, and times into a character type. The basic syntax for it is:

Convert an expression to a specified format.

The “expression” indicates the value to be converted, which can be a field or constant of types such as numeric, date, or time; “format” indicates the character format after conversion.

The to_char function is commonly used for the following purposes:

1. Numeric data type conversion: You can convert numeric data types to a specified character format. For example, to_char(12345.6789, ‘99999.99’) will return “12345.68”, and to_char(12345.6789, ‘9,999.99’) will return “12,345.68”.
2. Convert date types: it is possible to convert a date type to a character type with a specified format. For example, using to_char(sysdate, ‘YYYY-MM-DD’) will return the year, month, and date of the current date in the format “2022-01-01”.
3. Time type conversion: It is possible to convert the time type into a character type with a specified format. For example, using to_char(systimestamp, ‘HH24:MI:SS.FF3’) will return the current time in hours, minutes, seconds, and milliseconds as “12:34:56.789”.
4. Other types of transformations: you can also convert other types of data, such as boolean types, LOB types, etc.

You can choose the appropriate format for conversion according to specific needs. Oracle provides some built-in format models, such as ‘YYYY-MM-DD’ representing year-month-date, ‘HH24:MI:SS.FF3’ representing hour:minute:second.millisecond, and so on. In addition, you can also use some pattern elements to customize the conversion format, such as ‘YYYY’ for a 4-digit year and ‘MM’ for a 2-digit month. More detailed format models and pattern elements can be found in the Oracle official documentation.