Cast and Convert functions in SQL Server Part 28

Summary

In this SQL Server tutorial, the instructor Wenet explores the intricacies of data type conversion using CAST and CONVERT functions. The session clarifies when to use each function, highlighting that CAST adheres to ANSI standards, ensuring compatibility across databases, while CONVERT offers more flexibility, including the use of styles for formatting datetime. Practical examples demonstrate converting datetime to a string with specific formats and grouping data by date, emphasizing the importance of converting datetime to date when necessary. The tutorial also touches on concatenating data types and concludes with a comparison of CAST and CONVERT, recommending CAST for portability and CONVERT for its enhanced formatting capabilities.

Takeaways

• 😀 The session focuses on learning about the CAST and CONVERT functions in SQL Server, which are used to convert data from one type to another.
• 🔍 The CAST function is used to convert the data type of a column, such as changing the 'date of birth' from datetime to varchar for better display.
• 📊 The CONVERT function is similar to CAST but offers additional flexibility, including the ability to specify a 'style' parameter to control the format of the converted data.
• 📝 An example given is converting a datetime column to display the date in 'DD MM YYYY' format using the CONVERT function with style 103.
• ❗ It's important to note that the LENGTH parameter in CAST and CONVERT is optional and can be used to specify the length of the converted data.
• 📅 The CONVERT function is necessary when you want to control the formatting of date and time data types, which CAST does not support.
• 💡 SQL Server 2008 introduced the 'date' data type, allowing for easier extraction of date parts without converting to varchar, which was necessary in SQL Server 2005.
• 🔑 The script provides practical examples, such as concatenating an integer ID with a varchar name after converting the ID to varchar.
• 🧩 Grouping data by date requires converting the datetime data type to just the date part to aggregate correctly, which can be achieved using either CAST or CONVERT.
• 🌐 CAST is based on ANSI standards, making it more portable across different database applications, whereas CONVERT is specific to SQL Server and offers more functionality.

Q & A

What are the two functions in SQL Server used for data type conversion?

The two functions in SQL Server used for data type conversion are CAST and CONVERT.

What is the primary difference between the CAST and CONVERT functions?

The primary difference is that CONVERT has an optional style parameter, which CAST does not have. Additionally, CAST is based on ANSI standards, making it more portable across different database applications, while CONVERT is specific to SQL Server and offers more flexibility.

Why would you choose to use CAST over CONVERT in SQL Server?

You would choose to use CAST over CONVERT when portability is a concern, as CAST is based on ANSI standards and can be used across different database applications. It's also the choice when you do not need the style functionality provided by CONVERT.

How can you control the formatting of datetime data types in SQL Server?

You can control the formatting of datetime data types in SQL Server using the style parameter in the CONVERT function. This allows you to specify how the datetime should be displayed, for example, as 'DD MM YYYY' using style 103.

What is the purpose of the style parameter in the CONVERT function?

The style parameter in the CONVERT function is used to control the format of the output when converting datetime data types. It allows for various predefined formats to be applied to the converted data.

How can you obtain only the date part from a datetime data type in SQL Server?

To obtain only the date part from a datetime data type in SQL Server, you can use the CONVERT function with a style parameter that specifies only the date, such as style 1 ('YYYY-MM-DD') or style 101 ('YYYYMMDD'). Alternatively, you can convert the datetime to the 'date' data type using either CAST or CONVERT.

What is the syntax for using the CAST function in SQL Server?

The syntax for using the CAST function in SQL Server is: CAST (expression AS data_type [(length)]). The length is optional and depends on the target data type.

How do you concatenate a numeric column with a string column in SQL Server?

To concatenate a numeric column with a string column in SQL Server, you must first convert the numeric column to a string data type using either CAST or CONVERT, and then use the concatenation operator (+) to combine it with the string column.

What is the issue with grouping by a datetime column that includes both date and time in SQL Server?

Grouping by a datetime column that includes both date and time in SQL Server can result in no rows being grouped together because it's unlikely that multiple records will have the exact same date and time down to the second. To group by just the date, you should convert the datetime column to the 'date' data type using CAST or CONVERT.

How can you display a date in a custom format such as 'DD MM YYYY' in SQL Server?

You can display a date in a custom format such as 'DD MM YYYY' in SQL Server by using the CONVERT function with the appropriate style parameter, which in this case would be style 103.