Transforming Oracle Time Types: A Comprehensive Guide（oracle时间类型转换）

Transforming Oracle Time Types: A Comprehensive Guide

When working with the Oracle database, most developers will come across the various types of time-based data the database stores. Due to the subtle differences between Oracle data types, it’s important to understand how to transform between the different time types. This guide will provide an overview of the different types and how you can use SQL to convert from one to the other.

First and foremost, when dealing with time related data, Oracle distinguishes between two major types: DATE and TIMESTAMP. DATE is a basic type for storing only dates, and TIMESTAMP stores both date and time. Any operation involving time necessitates a conversion between one type to the other, and this can be accomplished with the TO_DATE and TO_TIMESTAMP SQL functions. The general syntax for the functions is shown below:

TO_DATE(char-expr string, [date-format]);

TO_TIMESTAMP(char-expr string, [date-format]);

The char-expr string is a character-based string representation of the date you intend to convert to a DATE or TIMESTAMP type and the optional date-format parameter is the format in which the string is provided.

For example, to transform a string of “20/05/2020” into a date type we would call the TO_DATE() function with the following syntax:

SELECT TO_DATE(’20/05/2020′, ‘DD/MM/YYYY’) FROM dual;

On the other hand, transforming a TIMESTAMP type requires specifying the exact format of the string representation.

SELECT TO_TIMESTAMP(’20/05/2020 21:30:00′, ‘DD/MM/YYYY HH24:MI:SS’) FROM dual;

When storing DATE and TIMESTAMP data types, Oracle uses a specific set of formats for maintaining consistency. The most commonly used formats are ‘DD-MON-YY’ for DATE, and ‘DD-MON-YY HH24:MI:SS’ for TIMESTAMP.

Finally, when reading DATE and TIMESTAMP values from the database, you can use the TO_CHAR function to make the data more readable. This function takes a DATE or TIMESTAMP value as input and converts it to a string representation with a given format. For instance, parsing a date value of ’20-MAY-20′ as “May 20th 2020” requires the following syntax:

SELECT TO_CHAR(date_column, ‘MONTH DDTH YYYY’) FROM table_name;

In conclusion, time-based data manipulation in Oracle requires an understanding of the various time types and the functions used to convert between them. The functions discussed in this document, TO_DATE(), TO_TIMESTAMP(), and TO_CHAR() serve as powerful tools to transform and work with time-based data. Knowing how to use these functions properly can mean the difference between a successful query and an error.