Method selectFromProvidedTable

engine/engine.go:244–304

(command *ast.SelectCommand, table *Table)

}

func (engine *DbEngine) selectFromProvidedTable(command *ast.SelectCommand, table *Table) (*Table, error) {
	columns := table.Columns

	wantedColumnNames := make([]string, 0)
	if command.AggregateFunctionAppears() {
		selectedTable := &Table{Columns: make([]*Column, 0)}

		for i := 0; i < len(command.Space); i++ {
			var columnType token.Token
			var columnName string
			var columnValues []ValueInterface
			var err error
			value := make([]ValueInterface, 0)
			currentSpace := command.Space[i]

			if currentSpace.ColumnName.Type == token.ASTERISK && currentSpace.AggregateFunc.Type == token.COUNT {
				if len(columns) > 0 {
					columnValues = columns[0].Values
				}
			} else {
				columnValues, err = getValuesOfColumn(currentSpace.ColumnName.Literal, columns)
			}

			if err != nil {
				return nil, err
			}

			if currentSpace.ContainsAggregateFunc() {
				columnName = fmt.Sprintf("%s(%s)", currentSpace.AggregateFunc.Literal,
					currentSpace.ColumnName.Literal)
				columnType = evaluateColumnTypeOfAggregateFunc(currentSpace)
				aggregatedValue, aggregateErr := aggregateColumnContent(currentSpace, columnValues)
				if aggregateErr != nil {
					return nil, aggregateErr
				}
				value = append(value, aggregatedValue)
			} else {
				columnName = currentSpace.ColumnName.Literal
				columnType = currentSpace.ColumnName
				value = append(value, columnValues[0])
			}

			selectedTable.Columns = append(selectedTable.Columns, &Column{
				Name:   columnName,
				Type:   columnType,
				Values: value,
			})
		}
		return selectedTable, nil
	} else if command.Space[0].ColumnName.Type == token.ASTERISK {
		for i := 0; i < len(columns); i++ {
			wantedColumnNames = append(wantedColumnNames, columns[i].Name)
		}
		return extractColumnContent(columns, &wantedColumnNames, command.Name.GetToken().Literal)
	} else {
		for i := 0; i < len(command.Space); i++ {
			wantedColumnNames = append(wantedColumnNames, command.Space[i].ColumnName.Literal)
		}