How to extract create statements from different tables of MySQL DBs? - mysql

Question

I would like to extract all Create Statements in my 50 MySQL Databases via SHOW CREATE TABLE db.table or SHOW CREATE TABLE db1.mytableor SHOW CREATE TABLE db2.sometableor SHOW CREATE TABLE db3.mytable1. Thus each of the DBs has some tables inside db1(table,mytable...) db2(table1,sometable) and so on
To illustrate the DBs via a example query:
SELECT *
FROM db.table1 m
LEFT JOIN db1.sometable o ON m.id = o.id
LEFT JOIN db2.sometables t ON p.id=t.id
LEFT JOIN db3.sometable s ON s.column='john'
library(RMySQL)
library(DBI)
con <- dbConnect(RMySQL::MySQL(),
username = "",
password = "",
host = "",
port = 3306,
dbname= mydbname)# when using dbs<-dbGetQuery(con ,"SHOW DATABASES") I have to ## dbname= mydbname## to get all DBs
Using dbs<-dbGetQuery(con ,"SHOW DATABASES")I can extract all 50 Databases in the dbConnection as character vector. I would like loop over each DB in the dbsand apply SHOW CREATE TABLE to each row/db. I suppose I have to parse the each row/db into dbname= mydbnameand dbs<-dbGetQuery(con ,"SHOW CREATE TABLE"). But I just cant figure out how to make the loops
I tried:
apply(dbs, 1, function(row) {
dbname <- row[]
for (i in 1:length(dbname)) {
create<-dbGetQuery(con,"SHOW CREATE TABLE") }
})
But that doesnt seem right. I suppose I have to include the con into the loop somehow. Otherwise I'll get:
Error in .local(drv, ...) : object 'dbname' not found
So I tried:
apply(dbs, 1, function(row) {
dbname <- row[]
for (i in 1:length(dbname)) {
con <- dbConnect(RMySQL::MySQL(),
username = "",
password = "",
host = "",
port = 3306,
dbname= [i])
create<-dbGetQuery(con,"SHOW CREATE TABLE") }})
I suppose that comes close to the solution but I miss something:
dbs<-dbGetQuery(con,"show databases")
library(foreach)
foreach(i = 1:(length(dbs))%dopar%{
query<-paste("SHOW CREATE TABLE",dbs[i])
creates<-dbGetQuery(con,query)
})

Answer 1

Consider this approach of importing a data frame of each database (leaving out the system ones, INFORMATION_SCHEMA and MYSQL) and their corresponding tables. Then, run SHOW CREATE TABLE statements. Finally, merge the original dataframe with binded dataframe of create statements.
Now, the one caveat is tables that repeat names across databases. To return distinct values of such combinations, the aggregate() by head function is used.
con <- dbConnect(RMySQL::MySQL(),
username = "****", password = "****",
host = "****", port = 3306,
dbname= "****")
dbtbls <- dbGetQuery(con, "SELECT `TABLE_SCHEMA` AS `Database`,
`TABLE_NAME` AS `Table`
FROM `INFORMATION_SCHEMA`.`TABLES`
WHERE `TABLE_TYPE` = 'BASE TABLE'
AND `TABLE_SCHEMA` NOT LIKE '%SCHEMA%'
AND `TABLE_SCHEMA` NOT LIKE '%MYSQL%' ")
# LIST OF SQL STATEMENTS
sql <- paste0("SHOW CREATE TABLE ", dbtbls$Database, ".", dbtbls$Table)
# LIST OF DATAFRAMES
createstmts <- lapply(sql, function(x) dbGetQuery(con, x))
dbDisconnect(con)
# ROW BIND LIST INTO ONE DATAFRAME TO MERGE WITH ORIGINAL
stmtsdf <- do.call(rbind, createstmts)
finaldf <- merge(dbtbls, stmtsdf, by='Table')
# RETURN DISTINCT RECORDS
finaldf <- aggregate(.~Database+Table, finaldf, FUN=head, 1)

Answer 2

mysqldump --no-data
does exactly what you are asking for. (There may be other parameters desirable to avoid/include CREATE DATABASE, etc.)
If the requirement is to subsequently pull the CREATEs into R, then I ask whether this is a one-time task, or a recurring task. For one-time, I would suggest that, overall, the mysqldump approach might be simpler.

Answer 3

First, you can just simply use
for (i in 1:length(dbs)) { }
Or you can look into apply functions, particularly, sapply. There you can do parsing per dbConnection string, connect and get all tables as list or vector. Then you can loop inside those to get create table statements.
So, it is basically apply inside apply.
For a good explanation of apply functions, you can look into http://www.r-bloggers.com/using-apply-sapply-lapply-in-r/