# Excel Format Plugin
This plugin enables Drill to read Microsoft Excel files. This format is best used with Excel files that do not have extensive formatting, however it will work with formatted files, by allowing you to define a region within the file where the data is. 

The plugin will automatically evaluate cells which contain formulae. 

## Plugin Configuration 
This plugin has several configuration variables which must be set in order to read Excel files effectively. Since Excel files often contain other elements besides data, you can use the configuration variables to define a region within your spreadsheet in which Drill should extract data. This is potentially useful if your spreadsheet contains a lot of formatting or other complications. 

### Configuration Options:
The most basic configuration is simply to add the following to a file based storage plugin:
```
"excel": {
   "type": "excel"
  }
```
The plugin has many other configuration options listed below:

* `headerRow`: Set to `-1` if there are no column headers. Defaults to `0`. If the data does not have a header row, Drill will assign column names of `field_n` for each column
. If the sheet starts with a series of empty rows, Drill will ignore these empty rows, so there is no need to set the `headerRow` in that case.
* `lastRow`: This defines the last row of data. The default is 1048576 which is the theoretical row limit for Excel files. It is only necessary to set this if you want Drill to
 stop reading at a specific location.
* `sheetName`: This is the name of the sheet which Drill will query. This will default to the first sheet in the file if left undefined. Drill will throw an exception if the
 sheet is not found.
* `firstColumn`: In order to define a region within a spreadsheet, this is the left-most column index. This is indexed from one. If set to `0` Drill will start at the left most
 column.
* `lastColumn`: To define a region within a spreadsheet, this is the right-most column index. This is indexed from one. If set to `0` Drill will read all available columns. This
 is not inclusive, so if you ask for columns 2-5 you will get columns 2,3 and 4. 
* `allTextMode`: When set to `true`, Drill will not attempt to infer column data types and will read everything as `VARCHAR`. Defaults to `false`;
* `maxArraySize`: Overrides the default [POI config](https://poi.apache.org/components/configuration.html) for `setByteArrayMaxOverride(int maxOverride)`. May be needed with large Excel files.
* `thresholdBytesForTempFiles`: Overrides the default [POI config](https://poi.apache.org/components/configuration.html) for `ZipInputStreamZipEntrySource.setThresholdBytesForTempFiles(int thresholdBytes)`. May be needed with large Excel files.
* `useTempFilePackageParts`: Overrides the default [POI config](https://poi.apache.org/components/configuration.html) for `ZipPackage.setUseTempFilePackageParts(boolean tempFilePackageParts)`. May be needed with large Excel files.

## Usage
You can specify the configuration at runtime via the `table()` function or in the storage plugin configuration. For instance, if you just want to query an Excel file, you could
 execute the query as follows:

```
SELECT <fields> 
FROM dfs.`somefile.xlsx`
```
To query a different sheet other than the default, use the `table()` function as shown below:
```
SELECT <fields> 
FROM table( dfs.`test_data.xlsx` (type => 'excel', sheetName => 'secondSheet'))
```
To join data together from different sheets in one file, use the query below:
```
SELECT <fields> 
FROM table( dfs.`test_data.xlsx` (type => 'excel', sheetName => 'secondSheet')) AS t1
INNER JOIN table( dfs.`test_data.xlsx` (type => 'excel', sheetName => 'thirdSheet')) AS t2 
ON t1.id = t2.id
```

### Implicit Columns
Drill includes several columns of file metadata in the query results. These fields are **not** included in star queries and thus must be explicitly listed in a query. 

The fields are:

    _category
    _content_status
    _content_type;
    _creator
    _description
    _identifier
    _keywords
    _last_modified_by_user
    _revision
    _subject
    _title
    _created
    _last_printed
    _modified
    _sheets


### Known Limitations:
At present, Drill requires that all columns be of the same data type. If they are not, Drill will throw an exception upon trying to read a column of mixed data type. If you are
 trying to query data with heterogenoeus columns, it will be necessary to set `allTextMode` to `true`. 

An additional limitation is that Drill infers the column data type from the first row of data. If a column is `null` in the first row, Drill will default to a datatype of
 `VARCHAR`. However if in fact the column is `NUMERIC` this will cause errors. 
 
 Drill ignores blank rows.

