Why am I seeing \"?????\" characters when retrieving UTF-8 text from MySQL in R?

UTF-8 Text Retrieval from MySQL in R: Decoding "?????"

Retrieving UTF-8 encoded text from a MySQL database into R can sometimes result in "?????" characters. To resolve this issue, consider the following:

1. Verify Database Encoding

Ensure that the database table is defined with the appropriate charset and collation. For example, in MySQL:

CREATE TABLE test (str VARCHAR(10)) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2. Set Connection Encoding

When establishing a database connection in R, specify the correct character encoding.

RODBC:

con <- odbcDriverConnect('DRIVER=mysql;user=root', CharSet='utf8')

RMySQL:

Connect first and then run:

dbConnect(MySQL(), user='root')
dbSendQuery(con, 'SET NAMES utf8')

3. Convert Character Encoding

After retrieving the results, convert the character encoding of the string column to UTF-8.

RODBC:

res <- sqlQuery(con, 'SELECT * FROM rtest.test')
res$str <- iconv(res$str, "UTF-8-Mac")

RMySQL:

res <- dbGetQuery(con, 'SELECT * FROM rtest.test')
res$str <- as.character(res$str, encoding = 'UTF-8')

Additional Notes:

• Ensure that the default system locale is set to UTF-8.
• For RMySQL, using dbSendQuery to set character encoding is effective for all subsequent queries.
• iconv can also be used to transcode strings to UTF-8, but its behavior can vary depending on the platform.

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