Execute SQL queries directly on one or more CSV files

[jeroenjanssens]

In #259, with the new tool sql2csv, it was already suggested that you could execute SQL queries directly on CSV files using a hacky bash script. Now, with these small changes to csvsql, you can truly execute SQL queries on one or more CSV files.

This functionality is similar to TextQL and Q. However, thanks to the solid codebase of csvkit, csvsql handles both multiple tables and proper escaping of output. The following example, which joins two data sets that can be found in the examples directory, illustrates the changes:

 < iris.csv csvsql --query 'select m.usda_id, avg(i.sepal_length) as mean_sepal_length from stdin as i join irismeta as m on (i.species = m.species) group by m.species' irismeta.csv | csvlook
|----------+--------------------|
|  usda_id | mean_sepal_length  |
|----------+--------------------|
|  IRSE    | 5.006              |
|  IRVE2   | 5.936              |
|  IRVI    | 6.588              |
|----------+--------------------|

Note that you can now mix standard input and filenames. It is no longer necessary to specify --table when standard input is provided. Tables based on standard input are named "stdin" by default. Table names can still be overridden by specifying a (comma delimited) string to --tables. When --query is specified and --db is not, sqlite:///:memory: is used as the connection string and --insert is set to True. Multiple SQL queries can be specified by using ";" as a delimiter. Only the output of the last query is outputted as CSV. This allows you to execute SQL queries in memory.

No functionality has been removed. Appropriate tests have been added. I'll write the corresponding documentation once these changes have been accepted.

[jeroenjanssens]

The Travis CI build is failing on two XLSX tests. Does anyone know why this happens?