CASE WHEN Expression — Conditional Transformation — Free SQL Tutorial
Learn CASE WHEN Expression — Conditional Transformation in SQL with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.
TL;DR: Learn CASE WHEN Expression — Conditional Transformation in SQL with a free, beginner-friendly tutorial, examples and practice for Indian students on S…
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CASE WHEN Expression — Conditional Transformation in SQL
CASE WHEN is SQL's if-then-else. It allows conditional logic directly inside SELECT queries to categorise data, create computed columns, and transform values.
Searched CASE evaluates multiple independent conditions. Simple CASE compares one expression to multiple values (like a switch statement). Both return the first matching WHEN value.
Conditional aggregation with CASE: SUM(CASE WHEN condition THEN 1 ELSE 0 END) counts rows matching a condition — enables pivot-style reports in standard SQL.
CASE WHEN Expression — Conditional Transformation — Syntax
-- Searched CASE (most common):
CASE
WHEN marks >= 90 THEN 'A+'
WHEN marks >= 80 THEN 'A'
ELSE 'C'
END AS grade
-- Conditional aggregation (pivot):
SUM(CASE WHEN marks >= 90 THEN 1 ELSE 0 END) AS a_plus_count
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