Last updated: 2023-10-08
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Knit directory: Pandas-30-R/
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| File | Version | Author | Date | Message |
|---|---|---|---|---|
| Rmd | 066a00f | Mena WANG | 2023-10-08 | first SQL tip |
Use RSQLite library allows us to run SQL queries in R
environment. We also have the option to create an in-memory database for
quick experimentation.
# Load the RSQLite library to use SQL in R
library(RSQLite)
# Create a SQLite database
# con <- dbConnect(SQLite(), dbname = "mydatabase.db")
# Create an SQLite in-memory database connection
con <- dbConnect(SQLite(), dbname = ":memory:")Sometimes we might want to use SQL query to extract specific element
of a field. On platforms such as Snowflake, I found
SPLIT_PART very helpful in such scenarios. For example, in
the query below, SPLIT_PART is used to extract the domain
name from a URL by first splitting the URL using ‘://’ as a delimiter
and then further splitting the result using ‘/’ as a delimiter to obtain
the domain name.
But the SPLIT_PART function is not supported in RSQLite,
so here in the demo I will show both the SPLIT_PART way and the
alternative that works in RSQLite.
# Create a dummy table with sample data
dbWriteTable(con, "url_demo", data.frame(
id = 1:4,
url = c(
'https://www.example.com/page1',
'https://www.example.com/page2',
'https://www.openai.com/research/',
'https://www.github.com/user/repo'
)
))
# Query that would have worked in Snowflake
query <- "
SELECT
id,
url,
SPLIT_PART(SPLIT_PART(url, '://', 2), '/', 1) AS domain_name
FROM
url_demo;
"
# Define the SQL query to extract domain names
query <- "
SELECT
id,
url,
SUBSTR(url, INSTR(url, '://') + 3, INSTR(SUBSTR(url, INSTR(url, '://') + 3), '/') - 1) AS domain_name
FROM
url_demo;
"
# Execute the SQL query
result <- dbGetQuery(con, query)
# Print the result
print(result) id url domain_name
1 1 https://www.example.com/page1 www.example.com
2 2 https://www.example.com/page2 www.example.com
3 3 https://www.openai.com/research/ www.openai.com
4 4 https://www.github.com/user/repo www.github.com
sessionInfo()R version 4.2.1 (2022-06-23 ucrt)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19045)
Matrix products: default
locale:
[1] LC_COLLATE=English_Australia.utf8 LC_CTYPE=English_Australia.utf8
[3] LC_MONETARY=English_Australia.utf8 LC_NUMERIC=C
[5] LC_TIME=English_Australia.utf8
attached base packages:
[1] stats graphics grDevices datasets utils methods base
other attached packages:
[1] RSQLite_2.3.1
loaded via a namespace (and not attached):
[1] Rcpp_1.0.11 pillar_1.9.0 compiler_4.2.1 bslib_0.5.0
[5] later_1.3.1 jquerylib_0.1.4 git2r_0.32.0 workflowr_1.7.0
[9] tools_4.2.1 bit_4.0.5 digest_0.6.33 memoise_2.0.1
[13] jsonlite_1.8.7 evaluate_0.21 lifecycle_1.0.3 tibble_3.2.1
[17] pkgconfig_2.0.3 rlang_1.1.1 cli_3.6.1 DBI_1.1.3
[21] rstudioapi_0.15.0 yaml_2.3.7 xfun_0.39 fastmap_1.1.1
[25] stringr_1.5.0 knitr_1.43 fs_1.6.2 vctrs_0.6.3
[29] sass_0.4.7 bit64_4.0.5 rprojroot_2.0.3 glue_1.6.2
[33] R6_2.5.1 fansi_1.0.4 rmarkdown_2.23 blob_1.2.4
[37] magrittr_2.0.3 whisker_0.4.1 promises_1.2.0.1 htmltools_0.5.5
[41] renv_1.0.0 httpuv_1.6.11 utf8_1.2.3 stringi_1.7.12
[45] cachem_1.0.8