Add translation for substring_index()

[ianmcook]

Add a translation for the MySQL function substring_index() as requested by @jimmyg3g in ianmcook/tidyquery#13

[ianmcook]

Translation for tidyverse = TRUE added in f984e89

[ianmcook]

Tests for when tidyverse = TRUE added in db8bc7e

[ianmcook]

Fixed a bug in 96e62ab

[ianmcook]

I'm not going to implement a translation for when tidyverse = FALSE right now because it's complicated by the lack of a string reverse function in base R.

[ianmcook]

@jimmyg3g if you install queryparser from GitHub, then restart R and load tidyquery, you should be able to run queries that use the substring_index() function. Let me know if this works for you! The command to install it from GitHub is:

devtools::install_github("ianmcook/queryparser")

I'll submit to CRAN along with some other changes sometime in the next few months.

[jimmyg3g]

@ianmcook Thanks, it's working for me. Thanks for sharing the link to it code too, fascinating to see how it works behind the scenes!