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Update Getting and Cleaning Data Course Notes.Rmd #22

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12 changes: 6 additions & 6 deletions 3_GETDATA/Getting and Cleaning Data Course Notes.Rmd
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Expand Up @@ -202,16 +202,16 @@ $\pagebreak$
* free/widely used open sources database software, widely used for Internet base applications
* each row = record
* data are structured in databases $\rightarrow$ series tables (dataset) $\rightarrow$ fields (columns in dataset)
* `dbConnect(MySQL(), user = "genome", db = "hg19", host = "genome-mysql.cse.ucsc.edu)` = open a connection to the database
* `con <- dbConnect(MySQL(), user = "genome", db = "hg19", host = "genome-mysql.cse.ucsc.edu)` = open a connection to the database
* `db = "hg19"` = select specific database
* `MySQL()` can be replaced with other arguments to use other data structures
* `dbGetQuery(db, "show databases;")` = return the result from the specified SQL query executed through the connection
* `dbGetQuery(con, "show databases;")` = return the result from the specified SQL query executed through the connection
* any SQL query can be substituted here
* `dbDisconnect(db)` = disconnects the open connection
* `dbDisconnect(con)` = disconnects the open connection
* crucial to disconnect as soon as all queries are performed
* `dbListFields(db, "name")` = returns the list of fields (columns) from the specified table
* `dbReadTable(db, "name")` = returns the the specified table
* `query <- dbSendQuery(db, "query")` = send query to MySQL database and store it remotely
* `dbListFields(con, "name")` = returns the list of fields (columns) from the specified table
* `dbReadTable(con, "name")` = returns the the specified table
* `query <- dbSendQuery(con, "query")` = send query to MySQL database and store it remotely
* `fetch(query, n = 10)` = executes query and returns the result
* `n = 10` = returns the first 10 rows
* `dbClearResult(query)` = clears query from remote database, important
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