Efficiently Calculating Grade Percentages from Unstructured Data with SQL

Storing grades as free text in a database presents challenges when calculating grade percentage distributions. This article offers SQL solutions to compute these percentages for all grades, even without predefined grade values.

SQL Query for Percentage Calculation

This SQL query leverages the over() function for efficient percentage calculation across unique grade values:

SELECT Grade, COUNT(*) * 100.0 / SUM(COUNT(*)) OVER ()
FROM MyTable
GROUP BY Grade;

The over() function computes the total row count across the entire table, enabling percentage calculation without needing to specify all possible grades.

Alternative SQL Query (for Databases without over() Function)

For databases lacking the over() function, this alternative query uses a subquery:

SELECT Grade, COUNT(*) * 100.0 / (SELECT COUNT(*) FROM MyTable)
FROM MyTable
GROUP BY Grade;

This approach employs a subquery to obtain the total row count, then calculates the percentages.

Important Note: These solutions accurately calculate percentages when grade data is stored as single-character values (e.g., 'A', 'B', 'C'). More complex grade formats within unstructured text require preprocessing to extract the grade values before applying these SQL queries.