Auto resolve expressions

[EpicStep]

As part of this task, it is necessary to implement the auto_resolve_expression setting. If it is enabled, then you need to generate an expression from system.columns.

Example:

package database

import (
	"context"
	"fmt"
	"strings"
)

type Column struct {
	Name              string
	Type              ColumnType
	AggregateFunction string
	IsSortingKey      bool
	IsPrimaryKey      bool
}

type ColumnType int

const (
	ColumnDefaultType ColumnType = iota + 1
	AggregateFunctionType
)

func (db *Database) Columns(ctx context.Context, database, table string) ([]Column, error) {
	var columns []Column

	rows, err := db.cluster.Query(ctx,
		`SELECT 
    				name, type, is_in_sorting_key, is_in_primary_key 
				FROM 
				    system.columns 
				WHERE 
				    database = $1 AND table = $2`, database, table)
	if err != nil {
		return nil, err
	}

	defer rows.Close()

	for rows.Next() {
		var column Column

		var typeString string

		if err = rows.Scan(&column.Name, &typeString, &column.IsSortingKey, &column.IsPrimaryKey); err != nil {
			return nil, err
		}

		column.Type = parseType(typeString)
		if column.Type == AggregateFunctionType {
			column.AggregateFunction = parseAggregateFunction(typeString)
		}

		columns = append(columns, column)
	}

	if len(columns) == 0 {
		return nil, fmt.Errorf("columns not found")
	}

	return columns, nil
}

func parseType(s string) ColumnType {
	if strings.HasPrefix(s, "AggregateFunction") {
		return AggregateFunctionType
	}

	return ColumnDefaultType
}

func parseAggregateFunction(s string) string {
	args := strings.TrimSuffix(strings.TrimPrefix(s, "AggregateFunction("), ")")
	splittedArgs := strings.Split(args, ",")

	return splittedArgs[0]
}