Simplifying SQL Data Conversion: A Developer’s Guide to SQL CONVERT

SQL developers often need to switch between data types. A number might need to be turned into a string, or a timestamp trimmed to just a date. SQL Server and MySQL offer the CONVERT function to help. Although it’s not part of the SQL standard, it serves as a helpful tool for data transformations. Here’s a clear guide to using it effectively.

Using SQL CONVERT in Real Scenarios

SQL Server

SELECT CONVERT(int, 42.35); -- Truncates to 42

Use the optional style parameter for formatting, especially with dates.

MySQL

SELECT CONVERT(42, CHAR); -- Converts to string '42'

Key use cases include:

• Convert string to date:

SELECT CONVERT('2024-01-18', DATE);

• Convert float to integer (rounding):

SELECT CONVERT(47.5, SIGNED); -- Returns 48

• Date to string:

SELECT CONVERT(NOW(), CHAR

You can also convert between character sets using:

SELECT CONVERT('Pelé' USING ASCII); -- Returns 'Pel?'

FAQ

Is CONVERT a universal SQL function?

No. It’s limited to systems like SQL Server and MySQL, with differing syntax and behavior.

Can I convert any type to any other type?

Not always. Some conversions may fail or trim data. Know your DBMS's rules.

How is CONVERT different from CAST?

CAST is standard SQL and widely supported. CONVERT is more flexible in some DBMSs.

Should I always use CONVERT?

Not necessarily. For better control, use functions tailored for specific data like DATE_FORMAT() in MySQL.

Conclusion

Understanding SQL CONVERT can save time and reduce typing errors in queries. Though non-standard, it’s a valuable function in SQL Server and MySQL. To read more, check out SQL CONVERT: The Handbook of Data Conversion in SQL.