Query from schema

A particularly attractive consequence of keeping all schemas in memory is that we can generate SQL queries based on them.

Here is a quick example to get you started.

import {
  BQView,
  BQField,
  Fragment,
  StringIdent,
  sql,
  fragments,
} from "@datoria/sdk";
import {
  analyticsDataset,
  dailyEventsTable,
} from "../../core-concepts/tables-and-partitioning.md";

function rewrite(f: BQField): [BQField, Fragment] | null {
  // pick `user_id` column as-is
  if (f.name === "user_id") {
    return [f, sql`${StringIdent(f.name)}`];
    // drop event_type column
  } else if (f.name === "event_type") {
    return null;
    // give all other columns an alias
  } else {
    const newField = { ...f, name: f.name + "_alias" };
    return [
      newField,
      sql`${StringIdent(f.name)} as ${StringIdent(newField.name)}`,
    ];
  }
}

const parts = dailyEventsTable.schema.map(rewrite).filter((x) => x !== null);

const query = sql`
  select ${fragments.joinWith(
    parts.map(([, f]) => f),
    sql`, `,
  )} 
  from ${dailyEventsTable.allPartitions()}
`;

const schema = parts.map(([f]) => f.asViewType());

export const person_event_rewritten_view = BQView({
  dataset: analyticsDataset,
  name: "person_event_rewritten",
  query,
  schema,
});

This is advanced functionality (and a contrived example), but hopefully the massive potential of this feature is clear