Search notes:

SQL data type: boolean

According to the SQL standared (ISO 9075), the boolean data type is an optional feature (with ID T031).

The values that can be assigned to a boolean are

true
false
null or unknown (unless specified as not null)

See also

SQL standard features E011 (Numeric types) and E021 (Character string types)

The bit data type in SQL Server

Oracle: boolean data type

Although SQLite does not have a boolean data type, it understands the keywords true and false which evaluate to 1 and 0, respectively.

SQL: data types