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Selecting modified data from rows

Selecting conditional data from rows

Let’s say we want to reduce the amount of variation in course data for a presentation and we want to display only “Ruby”, “Python” and “Others”. What it means is that if the course is anything other than “Ruby” or “Python” then instead of actual course name “Others” should be displayed.

For such cases, SQL provides a conditional operators which can be used to select data based on a condition over one or multiple columns in a row.

Note that the way conditional expressions in SQL are written, differs from database to database. We are using Sqlite3 for this course, where the conditional operator used is CASE. PostgreSQL, a popular relational database uses the exact same operator and syntax for expressing conditions. However, MySQL, another very popular database uses an IF syntax for conditional expressions. The same query would be written in MySQL as:

SELECT name, IF(course IN ('Python', 'Ruby'), course, 'Others')) as course
FROM students