Creating a QL chart in DataLens On-premises

QL charts have the same general settings and section settings as the dataset-based charts. Only certain measure settings are supported for chart fields.

At each step, you can undo/redo any change introduced within the current version.

To create a QL chart:

  1. Go to an existing database connection.
  2. Make sure the Raw SQL level → SQL to read setting is active in the connection.
  3. In the top-right corner, click Create QL chart.
  4. In the Query tab, enter your query using the SQL dialect of the database you are querying.
  5. In the bottom-left corner, click Run.

After the query runs, your data will be visualized.

Example of a ClickHouse® database query
SELECT Category, Month, ROUND(SUM(Sales))
FROM samples.SampleLite
WHERE Category in {{category}} -- Variable used in the selector
GROUP BY Category, Month -- Grouping by category and month
ORDER BY Category, Month -- Sorting by category and month

Adding selector parameters

In QL charts, you can control selector parameters from the Parameters tab in the chart editing area and use the Query tab to specify a variable in the query itself in {{variable}} format.

To add a parameter:

  1. Go to the Parameters tab when creating a chart.

  2. Click Add parameter.

  3. Set the value type for the parameter, e.g., date-interval.

  4. Name the parameter, e.g., interval.

  5. Set the default values, e.g., 2017-01-01 — 2019-12-31.

    image

    There are several ways to configure the parameters of the date, datetime, date-interval, and datetime-interval types:

    • Exact date to specify an exact value.
    • Offset from the current date to specify a relative value that will be updated automatically.

    Use presets to quickly fill in the values.

To manage parameter values on the dashboard, create a selector with manual input and specify a parameter name in the Field or parameter name field.

Intervals

The date-interval and the datetime-interval type parameters can be used in query code only with the _from and _to postfixes. For example, for the interval parameter set to 2017-01-01 — 2019-12-31, specify:

  • interval_from to get the start of the interval (2017-01-01).
  • interval_to to get the end of the interval (2019-12-31).
Query example
SELECT toDate(Date) as datedate, count ('Oreder ID')
FROM samples.SampleLite
WHERE {{interval_from}} < datedate AND datedate < {{interval_to}}
GROUP BY datedate
ORDER BY datedate

Substituting parameter values in a QL chart query

A QL chart gets parameter values from a selector as:

  • Single value if one element is selected.
  • Tuple if multiple values are selected.

If a query for ClickHouse® or PostgreSQL connections has the in operator before a parameter, the substituted value is always converted into a tuple. In the case of other connections, there is no automatic conversion. A query with the in operator will run correctly if you select one or more values.

Example of a query with in
SELECT sum (Sales) as Sales, Category
FROM samples.SampleLite
WHERE Category in {{category}} 
GROUP BY Category
ORDER BY Category

If the query has = before a parameter, the query will only run correctly if a single value is selected.

Example of a query with =
SELECT sum (Sales) as Sales, Category
FROM samples.SampleLite
WHERE Category = {{category}} 
GROUP BY Category
ORDER BY Category

Null choice in a selector and parameters

If a selector has no value selected and no default value is set for a parameter, a null value is provided to a query. In this case, all values will be selected in dataset-based charts, and the filter for the relevant column will disappear when generating a query.

To enable a similar behavior in QL charts, you can use a statement like this in your query:

AND
CASE
    WHEN LENGTH({{param}}::VARCHAR)=0 THEN TRUE
    ELSE column IN {{param}}
END

Undoing and redoing changes in charts

When editing a QL chart, you can now undo/redo any change introduced within the current version.

Useful links

ClickHouse® is a registered trademark of ClickHouse, Inc.

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