There are are many ways to compare data using transformations. Logical comparators are most often used in JOIN, LOOKUP, and FILTER statements and in case expressions.

Syntax	Data Types	Example	Explanation
IS NULL	Any	state IS NULL	Returns `true` when state is a true `null` value.
IS NOT NULL	Any	state IS NOT NULL	Returns `true` when state is anything other than a true `null` value.
IS EMPTY	Any	state IS EMPTY	Returns `true` when state is a true `null` value, a blank string (a string with no content `''` or a string containing only whitespace characters like spaces and tabs `' '`), an empty array (`[]`), or an array containing only blank strings and true nulls (`[' ', null]`)
IS NOT EMPTY	Any	state IS NOT EMPTY	Returns `true` when state is anything other than a true `null` value, a blank string (a string with no content `''` or a string containing only whitespace characters like spaces and tabs `' '`), an empty array (`[]`), or an array containing only blank strings and true nulls (`[' ', null]`)
==	Any	state == 'MA'	Returns `true` when state is equal to `'MA'`. Note that when one side of the comparator is `null` the final result will be `null`, for example, `'a' == null` returns `null`.
=	Any	state = 'MA'	Returns `true` when state is equal to `'MA'`. Note that when one side of the comparator is `null` the final result will be `null`, for example, `'a' == null` returns `null`.
!=	Any	state != 'MA'	Returns `true` when state is not equal to `'MA'`.Note that when one side of the comparator is `null` the final result will be `null`, for example, `'a' != null` returns `null`.
>	Any Numeric	cost > 10.0	Returns `true` when cost is greater than 10.0. Note that when one side of the comparator is `null` the final result will be `null`, for example, `5 > null` returns `null`.
>=	Any Numeric	cost >= 10.0	Returns `true` when cost is greater than or equal to 10.0. Note that when one side of the comparator is `null` the final result will be `null`, for example, `5 >= null` returns `null`.
<	Any Numeric	cost < 10.0	Returns `true` when cost is less than 10.0. Note that when one side of the comparator is `null` the final result will be `null`, for example, `5 \< null` returns `null`.
<=	Any Numeric	cost <= 10.0	Returns `true` when cost is less than or equal to 10.0. Note that when one side of the comparator is `null` the final result will be `null`, for example, `5 \<= null` returns `null`.

You can modify a logical comparator by using NOT to reverse its logic. Logical comparators can also be combined with AND and OR.

Tip: To provide additional flexibility, functions are also available for several of these logical comparators. For example, IS NULL and IS_NOT_EMPTY.

Examples of Using Logical Comparators

Keep (that is, filter down to) rows that have a populated company_name or have a populated parent_company_name:

FILTER company_name IS NOT EMPTY OR parent_company_name IS NOT EMPTY;

Look up the exchange rate of a currency for a given year by matching on exact values in the year and currency columns.

LOOKUP exchange_rate
FROM "currency_exchange.csv" AS currency_lookup
ON year == currency_lookup.year AND currency == currency_lookup.currency;

Create a new attribute price_in_words and set it to 'expensive' when the price is greater than 100. Otherwise, set it to 'cheap':

SELECT *,
CASE 
WHEN price > 100 THEN 'expensive' 
ELSE 'cheap' 
END AS price_category;