rquery
does not parse expression of the SQL
node. Thus it does not know which tokens are string-literals, and which are column names. To assist with this user can annotate column names with .[]
.
## Loading required package: wrapr
date_cutoff <- '2017-04-02'
td <- mk_td("df",
c("cust",
"trans_date",
"sales"))
ops <- td %.>%
select_rows_se(
.,
qe(trans_date <= str_to_date(.(date_cutoff), '%Y-%m-%d'))) %.>%
sql_node(
.,
qae(max_date = max(.[trans_date]),
const_col1 = "a'",
const_col2 = 'a"'),
mods = "GROUP BY .[cust]",
orig_columns = FALSE)
cat(format(ops))
## mk_td("df", c(
## "cust",
## "trans_date",
## "sales")) %.>%
## select_rows(.,
## trans_date <= str_to_date("2017-04-02", "%Y-%m-%d")) %.>%
## sql_node(.,
## max_date %:=% max( trans_date )
## const_col1 %:=% "a'"
## const_col2 %:=% "a\"";
## GROUP BY "cust",
## *=FALSE)
Notice how this renders into different SQL
for each of our two database descriptions.
db1 <- rquery_db_info(
identifier_quote_char = "'",
string_quote_char = '"')
cat(to_sql(ops, db1))
## SELECT
## max( 'trans_date' ) AS 'max_date',
## "a'" AS 'const_col1',
## "a\"" AS 'const_col2'
## FROM (
## SELECT * FROM (
## SELECT
## 'cust',
## 'trans_date',
## 'sales'
## FROM
## 'df'
## ) tsql_39051605868657797402_0000000000
## WHERE 'trans_date' <= str_to_date ( "2017-04-02" , "%Y-%m-%d" )
## ) tsql_39051605868657797402_0000000001 GROUP BY 'cust'
db2 <- rquery_db_info(
identifier_quote_char = '"',
string_quote_char = "'")
cat(to_sql(ops, db2))
## SELECT
## max( "trans_date" ) AS "max_date",
## 'a'' AS "const_col1",
## 'a\'' AS "const_col2"
## FROM (
## SELECT * FROM (
## SELECT
## "cust",
## "trans_date",
## "sales"
## FROM
## "df"
## ) tsql_28373732259551036882_0000000000
## WHERE "trans_date" <= str_to_date ( '2017-04-02' , '%Y-%m-%d' )
## ) tsql_28373732259551036882_0000000001 GROUP BY "cust"
Notice our included quote characters were translated. This is an unwanted side-effect of using the qae()
shortcut which does not tokenize, so it does not know which quotes are in which roles in the expression.
To override quote translation in the sql_node()
(which is simple string substitution without quote context or escaping) you must use the clunkier “build up a string as a list of tokens” (where sub-listed items are string literals and names are column names).
ops <- td %.>%
select_rows_se(
.,
qe(trans_date <= str_to_date(.(date_cutoff), '%Y-%m-%d'))) %.>%
sql_node(
.,
list(
"max_date" %:=% "max(.[trans_date])",
"const_col1" = list(list("a'")),
"const_col2" = list(list('b"'))),
mods = "GROUP BY .[cust]",
orig_columns = FALSE)
cat(format(ops))
## mk_td("df", c(
## "cust",
## "trans_date",
## "sales")) %.>%
## select_rows(.,
## trans_date <= str_to_date("2017-04-02", "%Y-%m-%d")) %.>%
## sql_node(.,
## %:=% max( trans_date )
## const_col1 %:=% list("a'")
## const_col2 %:=% list("b\"");
## GROUP BY "cust",
## *=FALSE)
## SELECT
## NA,
## "a'" AS 'const_col1',
## "b\"" AS 'const_col2'
## FROM (
## SELECT * FROM (
## SELECT
## 'cust',
## 'trans_date',
## 'sales'
## FROM
## 'df'
## ) tsql_95607919585418797632_0000000000
## WHERE 'trans_date' <= str_to_date ( "2017-04-02" , "%Y-%m-%d" )
## ) tsql_95607919585418797632_0000000001 GROUP BY 'cust'
## SELECT
## NA,
## 'a\'' AS "const_col1",
## 'b"' AS "const_col2"
## FROM (
## SELECT * FROM (
## SELECT
## "cust",
## "trans_date",
## "sales"
## FROM
## "df"
## ) tsql_32978445021045744555_0000000000
## WHERE "trans_date" <= str_to_date ( '2017-04-02' , '%Y-%m-%d' )
## ) tsql_32978445021045744555_0000000001 GROUP BY "cust"
Quotes within string literals are going to be a nightmare moving from db to db, so our advice is to try to avoid them.