What is a function
Like most other computer languages, SQL supports the use of functions to process data. Functions are generally executed on data, which provides convenience for data conversion and processing.
For example, rtrim(), which is used to remove spaces at the end of a string, is an example of a function.
Functions are not as portable as SQL. Code that can run on multiple systems becomes portable. Relatively speaking, most SQL statements are portable, and when there are differences between SQL implementations, these differences are usually not that difficult to deal with. The portability of functions is not strong. Nearly every major DBMS implementation supports functions that other implementations do not, and sometimes the differences are significant.
For the sake of code portability, many SQL programmers discourage the use of specially implemented functions. While this is beneficial, it is not always good for application performance. Without these functions, writing some application code would be difficult. Other methods must be used to achieve the work that the DBMS does very efficiently.
If you decide to use a function, you should make sure to comment the code so that you can accurately know the meaning of the SQL code you write in the future.
Most SQL implementations support the following types of functions:
1. Text for processing text strings (such as deletion or padding, converting values to uppercase or lowercase) function.
2. Numerical functions used to perform arithmetic operations on numerical data (such as returning absolute values and performing algebraic operations).
3. Date and time functions for processing date and time values and extracting specific components from these values (for example, returning the difference between two date times, checking date validity, etc.).
4. System function that returns special information being used by the DBMS (such as returning user login information, checking version details).
In this article, we first introduced functions. In the next few articles, we will introduce the specific usage of related functions in detail, including concepts, usage and examples, so that they can be better used at work.
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