@visactor/calculator v2.0.3

Data Analysis Calculation Tool: Calculator

Functionality/Input/Output

The tool inputs "Raw Detailed Data" obtained through analysis functions. Utilizing a query configuration structured similar to "SQL-like Query Syntax", it computes "Result Data".

The query calculation parameters are aligned with the structure of an "SQL Query Statement," and the methods for aggregation, filtering, and other computational processes are also in line with those in SQL. However, flexibility support is tailored according to the "Usage Scenarios", simplifying some syntax and functionalities of SQL.

Usage Example

A common SQL format example:

select <column>, ...
from <table>
where (... and ...)
group by ..., ...
having (... or ...)
order by ..., ...
limit 1000

Corresponding query configuration structure:

import { query, type Query } from '@visactor/vmind/calculator'

query({
  from: data,
  select: { columns: [...] },
  where: { ... },
  groupBy: [...],
  having: { ... },
  orderBy: [...],
  limit: 1000,
})

Specialized Support Capabilities

While aligning with SQL syntax and processing, some parts are simplified and specially supported according to "Usage Scenarios". Below are some examples of similarities and differences:

Simplifications

from section:

• Subqueries are not supported; scenarios requiring subqueries can be achieved by multiple invocations by the user.
• Simplified join support, union not supported.

join section:

• Supports only Left Join, Right Join, Inner Join, Cross Join as per current usage scenarios, does not support Full type joins.
• Supports only the basic using condition, equivalent to the simplest on condition for joining two fields with the same name. As there are no other use cases, there is no support for conditions like on between, on like.
• The join process is provided as a separate computational process, not described within the query({ from }) model. Its result is used as input for the from section.

select section:

• Only supports listing fields in select, does not support select *.
• Complex "expression" calculations are converted to extendable JavaScript calculation functions that can be passed in by users for row/group data calculations. For example,
  • id + 5 => { alias: 'id', column: ({ row }) => row.id + 5 }
  • sum(sale) / count(sale) => { alias: 'id', aggregate: ({ group }) => sum(group, 'sale') / count(group, 'sale') }
• Direct establishment of field aliases alias in select, but other query configurations do not support referencing aliases.

offset section:

• Currently does not support offset, only limit, as there are no use cases for offset, and its addition would be straightforward and unobstructed.

Calculation Functions:

Field-level distinct is completed before aggregation, e.g., count(distinct <column>).

• Support for complex "expression" calculations is converted into extendable JavaScript calculation functions, formatted as in select.
• Custom aggregate processing functions can be passed in by users as needed.

Data Format:

• Non-declarative field types, no internal validation of value formats and legality.
• Supports string, number, null format fields.
• Does not support Date / boolean type fields (no special judgments and processing).
  • If needed, Date types can be converted into basic ISO 8601 string format YYYY-MM-DD, equivalent to calculation as string.
• Target usage is static data / HTTP API / JavaScript-generated data, thus does not support infinite precision number types or high precision numbers stored as string for calculations.
• According to SQL equivalent format, values cannot have undefined, i.e., missing field values should be filled with null.
• Does not support JSON format fields (Map / Array).

Performance Optimization:

• As it is not a real database or SQL execution engine, it lacks optimizations like indexes, logical optimizers (query planners), execution optimizers.
• Without indexes, the filtering process iterates through all row data.
• Lacks a logical optimizer, such as simplification of where/having logic within equivalent ranges.
• Lacks execution logic optimization, like advancing the limit process or sorting process within equivalent ranges.

Special Support

• Adds support for custom sorting in order by (usage scenario-specific, not standard SQL support).

  • Does not support custom sorting for "aggregated

  calculation values" (no use case).

SQL Equivalent Processing

• Aggregation, filtering, sorting processes for null values align with SQL.

  • Sum/average calculations are limited to numerical values, non-numeric sums are treated as zero. Empty row data results in null (no calculation result).
  • In filtering, only the is null operator matches null values (=/!= are ineffective).
  • In ascending/descending sorting, null values follow SQL's default rules (NULLS LAST).

• In filtering options,

  • between comparison is the same as in SQL, a closed interval.
  • Includes type conversion in comparison operations involving number / string.
  • Only having can perform aggregate calculations on fields.

• Apart from group by, if there are aggregate functions in the select column, they are also aggregated (aggregated into one row).

  • Without group by, and if there are no aggregate functions in select, order by cannot use aggregate calculations alone.

Execution Process

The execution process within calculator for a query() call also fully references the general execution process of an SQL engine for a single SQL query.

A typical SQL query process includes the following steps:

1. Join / From
2. Where
3. Group By
4. Having
5. Order by
6. Select
7. Distinct
8. Offset / Limit

Except for where and select, the rest are optional steps.

In the execution process of the calculator's query() function, these step names and meanings are consistent with SQL.

1. From

In SQL, From identifies the "data source table" for providing data. In the query({ from }) function, there are no table entities; the from field is directly the row data itself from: Row[];.

In SQL, the "source table" in From can also be a virtual table, such as the result of another nested SQL query (subquery), e.g.,

select <column>
from (
  select <column>
  from <table>
  where ...
)
where ...

In query(), subquery syntax is not supported, but it can be achieved by nested calls by the user, e.g.,

query({
  from: query({
    from: data,
    select: { columns: [...] },
    where: { ... },
    ...
  }),

  select: { columns: [...] },
  where: { ... },
  ...
})

join

In SQL, join is a sub-clause of from, executed according to different join types (left / right / inner / full / exclude, etc.) and corresponding field matching rules. For each matched field, the corresponding M, N rows are selected from the left and right tables, respectively, forming a Cartesian product virtual table of M x N rows.

In the calculation library usage, join is provided as a separate computational process, not described within the query({ from }) model. Its result is used as input for the from section, used as follows:

query({
  from: leftJoin({
    left: query( ... ),
    right: query( ... ),
  }),

  select: { columns: [...] },
  where: { ... },
  ...
})

2. Where

Filters "Raw Detailed Data" (TableData) (un-grouped/non-aggregated data). In SQL syntax, filtering conditions support multiple nested and and or relationships.

In the query({ where }) function, the where field correspondingly supports different filtering conditions combined into a "tree structure" (filter tree) through multiple nested and and or.

3. Group By

Groups raw data based on one or more fields, outputting multiple "Grouped Data" sets, divided by different column values for subsequent aggregation calculations. Each group's data is aggregated separately.

SQL queries inherently return "row-level data," unable to represent a pivoted structure. The multiple pivoted structure is maintained internally during the Group By stage for grouping, and it's converted to a flat detail table structure when outputting.

The order of each group in the "Grouped Data" is maintained as the order of the first row of each group in the raw data. The order of all rows within each group is also maintained as their original relative order.

Group By only groups and does not perform aggregation calculations (count/sum ...).

4. Having

Applies filters to each group in "Grouped Data" (GroupedData). The filtering conditions have a tree-like logical structure similar to that in Where,

Aggregation Calculation

However, Having allows the use of "aggregate functions" during filter processing. It performs an "aggregate calculation" on all rows within a group, producing a single value used in filtering conditions,

having id > 5 and count(email) > 5 and count(distinct email) > 5

When fields not using aggregate functions are present, the first row of each group is used by default, effectively representing the entire group;

During aggregate calculations, the distinct keyword can be used for deduplication, indicating that the calculation is performed on a deduplicated set of values for that field;

5. Order By

Sorts the input data. Without a preceding Group By, the input is "raw detailed data" and sorting is based only on individual rows.

For "Grouped Data", "aggregate functions" can be used to determine the order of groups, with the aggregation process being the same as in Having;

Order By only changes the order of groups in "Grouped Data", not the order of the original detailed rows within each group;

Manual Sorting

In platform use cases, "Manual Sorting" is implemented by converting manually set order values into case when statements in the Order By part of SQL statements, like:

order by case
  when name = '...' then 1
  when name = '...' then 2
  when name = '...' then 3
  else 4
end ASC

In the query() function, there is no support for case when, but manual sorting configurations are added in the orderBy field.

6. Select

Select is used to "extract" specific field columns from the output data. This process involves two steps:

• If the input is "Grouped Data", it aggregates each group into a single row (row) through aggregation calculations, similar to those in Having; Essentially transforming "Grouped Data" into "detailed data" rows equal in number to the groups.
• "Extracts" fields from each row and sets corresponding aliases.

7. Distinct

This is equivalent to the SQL syntax select distinct ..., indicating deduplication of rows in the final output data of Select.

8. Offset/Limit

Truncates the output data to the first N items, or offsets by the first M items before truncating to N items.