问题描述
我试图获取dbGetQuery来从SybaseIQ表(test_in)中检索字符列表(test_ID2)中引用的所有行.结果是仅检索到test_ID2中的第一个条目.
I am trying to get dbGetQuery to retrieve all rows referenced in a char list (test_ID2) from a SybaseIQ table (test_in). The result is that only the first entry in test_ID2 is retrieved.
dbGetQuery()看起来像这样:
the dbGetQuery() looks like this:
test_con <- DBI::dbConnect(odbc::odbc(),
driver = 'SybaseIQ',
host = 'xxx.xx.xxx',
port = 'xxxx',
uid = 'xxxx',
pwd = 'xxxx')
test_out <- dbGetQuery(test_con,"SELECT * FROM test_in WHERE ID2 = ?",
params = list(test_ID2))
test_in看起来像这样:
test_in looks like this:
> test_in
ID1 DATE ID2 QTY
115 18383M472 2017-02-01 93964W108 594
116 18383M472 2017-02-01 939653101 254
117 18383M472 2017-02-01 948741103 437
118 18383M472 2017-02-01 95040Q104 1236
119 25459W458 2017-02-01 G5876H105 4542
120 25459W458 2017-02-01 N07059210 557
121 25459W458 2017-02-01 N6596X109 1205
122 25459W458 2017-02-01 Y09827109 1401
123 25459W458 2017-02-01 007903107 8223
124 25459W458 2017-02-01 032654105 1609
125 25459W458 2017-02-01 038222105 3709
test_ID2看起来像这样:
test_ID2 looks like this:
> test_ID2
[1] "939653101" "N6596X109" "N99999999"
上述dbGetQuery()的结果仅包含一个条目
the result from the above dbGetQuery() contains only one entry
> test_out
ID1 DATE ID2 QTY
116 18383M472 2017-02-01 939653101 254
，它丢失了ID2 ="N6596X109"的条目.
and it misses the entry with ID2 = "N6596X109".
我做错什么了吗?
感谢您的想法！
更新
似乎有效的方法是使用 glue_sql()以及 dbSendQuery()和 dbFetch()
what seems to work is using glue_sql() along with dbSendQuery() and dbFetch()
test_ID2 <- as.character(test_ID2)
detail_qry <- glue_sql("select * from test_in where ID2 IN ({ID2*})",
ID2 = test_ID2, .con = test_con)
details <- dbSendQuery(test_con,detail_qry)
test_out <- dbFetch(details)
我仍然很好奇为什么以前的代码不起作用.似乎更直接.
I am still curious to understand why the previous code doesn't work. It seems to be more direct.
推荐答案
在SQL中，可以更有效地重用已准备好的语句.这样，使用绑定参数的预备语句可以受益，因此在需要重用查询时，使用无数据的预备语句可以利用此优势.(诚然，这里有些挥舞之手，坦白地说，...现在，我将提供它作为 glue_sql 的替代方法.)
In SQL, prepared statements can be reused more efficiently. With this, prepared statements that use bound parameters can benefit, so using a data-less prepared statement can take advantage of this when you need to reuse the query. (There is a little hand-waving going on here, admittedly ... for now, I'll just offer this as an alternative to glue_sql.)
从普通的SQL查询开始，演示了我们如何提供简单集合(使用 params = ).
Starting with a vanilla SQL query, a demonstration of how we want simple sets to be provided (using params=).
# con <- DBI::dbConnect(...)
DBI::dbGetQuery(con, "select 1 where 1 in (1,2)")
#
# 1 1
DBI::dbGetQuery(con, "select 1 where 1 in (?,?)", params=list(1,2))
#
# 1 1
DBI::dbGetQuery(con, "select 1 where 1 in (?,?)", params=list(2,3))
# [1]
# <0 rows> (or 0-length row.names)
让我们稍微正式一点:
DBI::dbWriteTable(con, "testcars", mtcars)
cyls <- c(4, 6)
qry <- sprintf("select * from testcars where cyl in (%s)", paste(rep("?", length(cyls)), collapse = ","))
qry
# [1] "select * from testcars where cyl in (?,?)"
通常，R用户将只使用 DBI :: dbGetQuery 进行一次查询，并可以选择绑定参数.但是，如果您有详尽的查询和/或需要提高查询速度，则可以执行多个步骤.(我目前无法立即量化这种差异.)通常，这些步骤是:
Normally, R users will just use DBI::dbGetQuery for a one-shot query, optionally with bound parameters. However, you can do a multi-step if you have an elaborate query and/or need some improvement in query speed. (I cannot off-hand quantify this difference at the moment.) The steps are typically:
- 发送查询/声明；
- 可选地绑定参数；
- 获取数据；最后
- 关闭结果集.
res <- DBI::dbSendQuery(con, qry)
res
# <OdbcResult>
# SQL select * from testcars where cyl in (?,?)
# ROWS Fetched: 0 [complete]
# Changed: 0
res2 <- DBI::dbBind(res, list(2, 4))
DBI::dbFetch(res2)
# row_names mpg cyl disp hp drat wt qsec vs am gear carb
# 1 Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
# 2 Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
# 3 Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
# 4 Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
# 5 Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
# 6 Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
# 7 Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
# 8 Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
# 9 Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
# 10 Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
# 11 Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
我们可以通过绑定新参数(无需新查询)来重用该查询(特别是 res ult集):
And we can reuse that query (that result set, specifically) with binding new parameters (without a new query):
res2 <- DBI::dbBind(res, list(6, 7))
DBI::dbFetch(res2)
# row_names mpg cyl disp hp drat wt qsec vs am gear carb
# 1 Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
# 2 Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
# 3 Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
# 4 Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
# 5 Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
# 6 Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
# 7 Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
DBI::dbClearResult(res2)
这篇关于R，dbGetQuery()不会为参数中传递的所有值选择记录的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！