LAST_INSERT_ID() always returns 0 (RMySQL) - separate connection issue

问题

Original example as found in some post

According to this post the following SQL statements should give me a vector 1, 2, 2, 2, 2 in the end:

require("RMySQL")
con <- dbConnect(
    dbDriver("MySQL"),
    db="your_db",
    user="your_user",
    password="your_pw", 
    host="localhost"
)
> con
<MySQLConnection:(6640,122)> 
> dbSendQuery(con, "DROP TABLE IF EXISTS t;")
<MySQLResult:(6640,122,0)> 
> dbSendQuery(con, "CREATE TABLE t (i INT NOT NULL AUTO_INCREMENT PRIMARY KEY);")
<MySQLResult:(6640,122,1)> 
> dbSendQuery(con, "INSERT INTO t VALUES(NULL);")
<MySQLResult:(6640,122,2)> 
> dbGetQuery(con, "SELECT LAST_INSERT_ID() FROM t;")
  LAST_INSERT_ID()
1                0
> dbSendQuery(con, "INSERT INTO t VALUES(NULL),(NULL),(NULL);")
<MySQLResult:(6640,122,3)> 
> dbGetQuery(con, "SELECT LAST_INSERT_ID() FROM t;")
  LAST_INSERT_ID()
1                0
2                0
3                0
4                0

Following suggestions by N.B., Jeff Allen and Quassnoi

Adapted the example to have it resemble real use cases a bit more than the original one:

dbSendQuery(con, "DROP TABLE IF EXISTS t;")
dbSendQuery(con, paste("CREATE TABLE t", 
    "(i INT NOT NULL AUTO_INCREMENT PRIMARY KEY, x INT);"))
> dbGetQuery(con, "SELECT CONNECTION_ID();")
  CONNECTION_ID()
1          673490
dbSendQuery(con, "INSERT INTO t SET x=1;")
> dbGetQuery(con, "SELECT CONNECTION_ID();")
  CONNECTION_ID()
1          673491
> dbGetQuery(con, "SELECT LAST_INSERT_ID();")
  LAST_INSERT_ID()
1                0
> dbGetQuery(con, "SELECT CONNECTION_ID();")
  CONNECTION_ID()
1          673493
> dbGetQuery(con, "SELECT LAST_INSERT_ID();")
  LAST_INSERT_ID()
1                0
dbSendQuery(con, "INSERT INTO t SET x=2;")
> dbGetQuery(con, "SELECT LAST_INSERT_ID();")
  LAST_INSERT_ID()
1                0
> dbGetQuery(con, "SELECT * FROM t;")
  i x
1 1 1
2 2 2

Well, it doesn't, really ;-)

I've googled a bit and AFAIU, LAST_INSERT_ID() is "connection-aware" in the sense that the same connection must be used if it is to work properly. However, I thought that by assigning the connection object to con I was making sure that indeed the same connection is used in each of the statements above.

Well, apparently not ;-) Can anyone help me out with some explanations and/or workarounds? Using something like select max(<ID>) from <TABLE> isn't going to cut it, though, as I'm running multiple threads that simultaneously write to the DB, thus messing up ID retrieval if done that way.

Thanks!

Findings as of 2012-04-20

Thanks to Quassnoi I was able to track down the problem a bit more. Seems like RMySQL functions don't really care about the explicit conn argument that much but open new connections in the background every time you connect to the DB. Probably some good reasons for this, too. Yet, does anyone know how to avoid this?
Just contacted Jeffrey Horner (maintainer of the RMySQL package). Seems like this is a Windows problem. Worked for him on Linux :-/

Connection details

As suggested by Jeff

> dbGetInfo(con)
$host
[1] "localhost"

$user
[1] "your_user"

$dbname
[1] "your_db"

$conType
[1] "localhost via TCP/IP"

$serverVersion
[1] "5.5.20"

$protocolVersion
[1] 10

$threadId
[1] 673489

$rsId
$rsId[[1]]
<MySQLResult:(6640,171,3)> 


> dbGetInfo(dbDriver("MySQL"))
$drvName
[1] "MySQL"

$connectionIds
$connectionIds[[1]]
<MySQLConnection:(6640,149)> 

$connectionIds[[2]]
<MySQLConnection:(6640,112)> 

$connectionIds[[3]]
<MySQLConnection:(6640,171)> 


$fetch_default_rec
[1] 500

$managerId
<MySQLDriver:(6640)> 

$length
[1] 16

$num_con
[1] 3

$counter
[1] 179

$clientVersion
[1] "5.5.20"

> dbListConnections(dbDriver("MySQL"))
[[1]]
<MySQLConnection:(6640,149)> 

[[2]]
<MySQLConnection:(6640,112)> 

[[3]]
<MySQLConnection:(6640,171)>

回答1:

I found a working solution here. It's also mentioned in stephan mc's reply, but as the second option. The first one didn't work for me, so I figured this might be worth highlighting more.

Anyways, the trick is to run dbClearResult() between the INSERT and SELECT LAST_INSERT_ID():

> library("RMySQL")
> con <- dbConnect(MySQL())
> dbSendQuery(con, "DROP TABLE IF EXISTS t;")
> dbSendQuery(con, "CREATE TABLE t (i INT NOT NULL AUTO_INCREMENT PRIMARY KEY);")
> res <- dbSendQuery(con, "INSERT INTO t VALUES (NULL);")

# doesn't work:
> dbGetQuery(con, "SELECT LAST_INSERT_ID();")
  LAST_INSERT_ID()
1                0

# works:
> dbClearResult(rs)
> dbGetQuery(con, "SELECT LAST_INSERT_ID();")
  LAST_INSERT_ID()
1                1

回答2:

You're inserting NULL values into the Primary Key column. Since you can't have two rows with the same PK, you're probably not actually inserting any real data (which is also probably an error you want to catch). Try:

dbSendQuery(con, "INSERT INTO t VALUES(5);")

Executing that should give you two different values for last_insert_id.

Edit: misunderstood. See here for the details on LAST_INSERT_ID. Revised answer: if you don't specify a value in an AUTO_INCREMENT column, then you should get a LAST_INSERT_ID value returned. In that case, try:

INSERT INTO t DEFAULT VALUES

回答3:

We found a very interesting solution:

res <- dbSendQuery(con, "INSERT INTO t VALUES (5);")
res <- dbSendQuery(con, "SELECT LAST_INSERT_ID();")
fetch(res)

If it does not work, use a dbClearResult(res) before sending the last id request. For us it worked out.

来源：https://stackoverflow.com/questions/10246412/last-insert-id-always-returns-0-rmysql-separate-connection-issue

标签

mysql

rmysql

last-insert-id