Summarize Row Counts by Dynamic Columns into JSON — From SQL to SPL #22

Problem description & analysis:

Each column of database table tempdata can be viewed as an array, with duplicate members:

Task: Now we need to group and count each column separately, in JSON format:

Code comparisons:

SQL:

With Grouped AS (
    SELECT
      td.hobbies_1,
      td.hobbies_2,
      COUNT(*) AS count
    FROM _temp_data td
    GROUP BY GROUPING SETS (
      (td.hobbies_1),
      (td.hobbies_2)
    )
)
SELECT
  jsonb_object_agg(g.hobbies_1, g.count) FILTER (WHERE g.hobbies_1 IS NOT NULL) AS hobbies_1,
  jsonb_object_agg(g.hobbies_2, g.count) FILTER (WHERE g.hobbies_2 IS NOT NULL) AS hobbies_2
FROM Grouped g;

First uses GROUPING SETS to group and count different columns simultaneously, and then uses jsonb_object_agg to convert each record set into JSON separately. The code is quite cumbersome; And the column names must be written, which is less flexible; If you want to support dynamic column names, you need to use stored procedures, and the structure will become complex.

SPL: SPL does not need to write column names: 👉🏻Try.DEMO.

A1： Load data.

A2： Transpose the two-dimensional table A1 into a sequence of sequences, group and count each small sequence (corresponding to each column), and then convert it into Json. Function E is used to convert between sequences and table sequences. @p represents the transpose of the two-layer sequence, @b represents removing the column name. When converting a set of records to JSON, there is an extra [] symbol compared with converting a record. Here, (1) is used to take the unique record and then convert it.

A3： Create a new empty two-dimensional table according to the A1 structure and fill in the Json sequence A2.

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