Conditional logic with CASE statements

Data Manipulation in Snowflake

Jake Roach

Field Data Engineer

Using ELSE

Sometimes, there might be additional values that don't fall into a WHEN ... THEN statement.

Use ELSE to capture these additional scenarios
Great way to catch edge cases

SELECT
    student,
    CASE
        WHEN grade_num = 12 THEN 'Senior'
        WHEN grade_num = 11 THEN 'Junior'
        ...
        ELSE 'Not in HS'  -- Catch others!
    END AS grade
FROM students;

          |   student  |    grade   |
          | ---------- | ---------- |
          |  Viraj     |  Junior    |
          |  Stephanie |  Senior    |
          |  Lewis     |  Not in HS |

Evaluating a condition

Operator	Condition	Example
`=`	Value is equal to another value	`column_a = 'value_a'`
`IN (...)`	Value is in a list of values	`column_a IN ('value_a', 'value_b')`
`>`, `<`	Value is greater than or less than another value	`column_a > 0`
`>=`, `<=`	Counterparts to `>` and `<`, also includes equality	`column_a >= 0`
`BETWEEN`	Value is between two values, inclusive	`column_a BETWEEN 0 AND 10`

These comparison operators can be combined with AND, OR, or NOT

CASE statements in Snowflake are efficient due to being a column-oriented database

Categorizing temperatures

SELECT
    todays_date,
    temperature,
    CASE

        WHEN temperature BETWEEN 70 AND 90 THEN 'Ideal for Swimming'

        WHEN temperature >= 50 AND tempreature < 70 THEN 'Perfect for Sports'

        WHEN temperature > 32 AND temperature < 50 THEN 'Spring/Fall Temps'
        WHEN temperature > 0 AND temperature <= 32 THEN 'Winter Weather'
        ELSE 'Extreme Temperatures'

    END AS temperature_description
FROM weather;

Categorizing temperatures

A table with the results of a CASE statement categorizing records by their temperature

Combining conditional statements

SELECT
    todays_date,
    temperature,
    status,

    CASE
        WHEN temperature > 70 AND status NOT IN ('Rain', 'Wind') THEN 'Beach'

        WHEN temperature BETWEEN 45 AND 70 AND status = 'Sun' THEN 'Sports'

        WHEN temperature <= 32 OR status = 'Snow' THEN 'Skiing'

        ELSE 'Stay In'
    END AS activity   
FROM weather;

We can evaluate multiple columns in a single CASE statement

Combining conditional statements

A table with the results of a CASE statement categorizing records by their temperature and outdoor status

Let's practice!

Data Manipulation in Snowflake