How to use a calculated column to calculate another column in the same view
Use a Common Table Expressions (WITH
clause) to create a computation layer or inline the calculation in the final select. Compute the first calculated column, then reference it for the second calculation:
Here, first_calc is calculated in the CTE and reused in the main query for second_calc. This technique ensures correct sequencing of calculations while maintaining readability.
Crafting queries efficiently
Things can get messy with complex SQL computations. Here are the tools to keep it tidy:
Nested queries
If simplicity is the goal, a nested query does wonders:
Cross apply in SQL Server
CROSS APPLY: Your handy sidekick when joining becomes a nuisance:
Optimal use of functions
Using functions? Choose ones that don't slow things down:
The delicate art of performance optimization
Performance can make or break your SQL queries, especially with calculated columns:
When it pays to repeat calculations
If a calculation is light, it might not hurt to repeat it:
Conditional play with case expressions
In SQL, we have case expressions where you set the calculation rules:
Advanced computation techniques
For off-the-beaten-path scenarios, SQL stands ready:
Leveraging APPLY in Oracle
It's called LATERAL in Oracle 12c+, but it's the same as SQL Server's APPLY:
Use CTE with OFFSET/FETCH for pagination
With Common Table Expressions and OFFSET/FETCH, you get calculated columns and pagination all in one:
Validating calculations with sample data
Insert mock data using INSERT INTO to validate your view's calculations:
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