Method join

packages/reltab/src/QueryExp.ts:148–160

(
    rhs: QueryExp,
    on: string | Array<string>,
    joinType: JoinType = "LeftOuter"
  )

  // join to another QueryExp
  join(
    rhs: QueryExp,
    on: string | Array<string>,
    joinType: JoinType = "LeftOuter"
  ): QueryExp {
    return new QueryExp({
      operator: "join",
      joinType,
      on,
      rhs: rhs._rep,
      lhs: this._rep,
    });
  }

  // distinct values of a column
  // just a degenerate groupBy: