@uwdata/mosaic-core
Version:
Scalable and extensible linked data views.
105 lines • 3.69 kB
JavaScript
import { Query, asTableRef, count, isAggregateExpression, isNode, isNull, max, min, sql } from '@uwdata/mosaic-sql';
import { jsType } from './js-type.js';
export const Count = 'count';
export const Nulls = 'nulls';
export const Max = 'max';
export const Min = 'min';
export const Distinct = 'distinct';
export const Stats = { Count, Nulls, Max, Min, Distinct };
const statMap = {
[Count]: count,
[Distinct]: column => count(column).distinct(),
[Max]: max,
[Min]: min,
[Nulls]: column => count().where(isNull(column))
};
/**
* Get summary stats of the given column
* @param field Field information request
* @returns Query for field statistics
*/
function summarize({ table, column, stats }) {
return Query
.from(table)
.select(Array.from(stats, s => ({ [s]: statMap[s](column) })));
}
/**
* Queries information about fields of a table.
* If the `fields` array contains a single field with the column set to '*',
* the function will retrieve and return the table information using `getTableInfo`.
* Otherwise, it will query individual field information using `getFieldInfo`
* for each field in the `fields` array.
* @param mc A Mosaic coordinator.
* @param fields Array of field information requests.
* @returns Promise resolving to array of field information.
*/
export async function queryFieldInfo(mc, fields) {
if (fields.length === 1 && fields[0].column === '*') {
return getTableInfo(mc, fields[0].table);
}
else {
return (await Promise
.all(fields.map(f => getFieldInfo(mc, f))))
.filter((x) => x !== undefined);
}
}
/**
* Get information about a single field of a table.
* @param mc A Mosaic coordinator.
* @param field Field information request.
* @returns Promise resolving to field information.
*/
async function getFieldInfo(mc, { table, column, stats }) {
const isAggregate = isNode(column) && isAggregateExpression(column);
// generate and issue a query for field metadata info
// use GROUP BY ALL to differentiate & consolidate aggregates
const q = Query
.from({ source: table })
.select({ column }, isAggregate ? '*' : {})
.groupby(isAggregate ? sql `ALL` : []);
let desc;
try {
[desc] = Array.from(await mc.query(Query.describe(q)));
}
catch {
// provide dummy description node upon query failure
// this handles true aggregates within window functions
// DuckDB fails to handle these when using GROUP BY ALL
desc = {
column_name: 'column',
column_type: 'DOUBLE',
null: 'YES'
};
}
const info = {
table,
column: `${column}`,
sqlType: desc.column_type,
type: jsType(desc.column_type),
nullable: desc.null === 'YES'
};
// no need for summary statistics
if (!stats?.length)
return info;
// query for summary stats
const [result] = await mc.query(summarize({ table, column, stats }), { persist: true });
// extract summary stats, copy to field info, and return
return Object.assign(info, result);
}
/**
* Get information about the fields of a table.
* @param mc A Mosaic coordinator.
* @param table The table name.
* @returns Promise resolving to array of field information.
*/
async function getTableInfo(mc, table) {
const result = Array.from(await mc.query(`DESC ${asTableRef(table)}`));
return result.map(desc => ({
table,
column: desc.column_name,
sqlType: desc.column_type,
type: jsType(desc.column_type),
nullable: desc.null === 'YES'
}));
}
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