Type Coercion and Precision in SQL
Why does 6/4 = 1?
In this article, I dive into how a seemingly simple calculation can yield unexpected results across different Database Management Systems (DBMS). One classic example is the division operation 6/4. You might expect 1.5, but in some Database Management Systems (DBMS), you'll get 1 instead. Why? It's all about integer division and type coercion.
I explore:
1.???? The nuances of division across different DBMS (PostgreSQL, MySQL, SQL Server, Oracle, SQLite)
2.???? Why 6/4 can equal 1 in some systems and 1.5 in others
3.???? The critical importance of explicit type casting (e.g., SELECT 6::FLOAT / 4)
4.???? How type coercion works in SQL and why it matters
5.???? Real-world scenarios where changing column types can break existing queries
6.???? The concept of "defensive SQL" and when to cast explicitly
7.???? An experiment demonstrating precision differences between DECIMAL and FLOAT types
Always be aware of your types, and when in doubt, cast explicitly.
#SQLTips #DataEngineering #DatabaseManagement
Software Engineer I at Raytheon Intelligence and Space | TS/SCI Security Clearance | Computer Science Graduate
8 个月Very well done article, Sam. Highly recommend for anyone to read no matter what your background is in. Sam does a great job at breaking down the key concepts to understand the topic at hand. From a software perspective, I’d like to add on when we would want to consider using integers vs floats vs doubles, or specifically precision. This is an important decision as unrestricted use of doubles can heavily impact performance while integers lack precision for many cases where going down to the decimal is necessary. A more in-depth overview can be found here. https://www.ilikebigbits.com/2017_06_01_float_or_double.html