The most convenient and useful thing in Redash is parameters. Parameters can be both in a report and in dashboards.
Parameter – is an element of the interface, controlled by a user producing a report.

Parameter in a report can be of the following types:

Each type explained separately:

• Text – text input field, can be used in constructions of LIKE type, such parameter can’t be applied in public dashboards
• Number – number, entered by a user
• Dropdown list – list of values, from which a user can select just one or several values (not long ago, an option of multi-entry of parameters in a dropdown list appeared)
• Query dropdown list – similarly to the previous one, however the values will be taken from the existing query results
• Date / Date and Time / Date and Time (with seconds) – fields of date entry
• Date Range / Date and Time Range / Date and Time Range (with seconds) – fields of date ranges entry.
  It’s convenient to use for the following construction

between '{{parameter.start}}' and '{{parameter.end}}'

In case of dashboard, a situation might arise, when a parameter is named the same way in several queries, then it will become common for all the dashboard, it’s handy.

One of not obvious, but rather useful solutions: how to make a parameter disabled?
Let’s assume, that parameter of “dropdown list” type is named parameter and we want to set it for a column geo of a table, then the code of the query will look approximately like that:

WHERE
    ('{{parameter}}' = 'Disabled' or geo = '{{parameter}}')

At that, surely, ‘Disabled’ should be added to the values of the dropdown list.