160-anti-join-cost-comparisons.Rmd

# Anti-join cost comparisons {#chapter_anti-join-cost-comparisons}

```{r setup, echo=FALSE, message=FALSE, warning=FALSE}
# These packages are called in almost every chapter of the book:
library(tidyverse)
library(DBI)
library(RPostgres)
library(glue)
library(here)
require(knitr)
library(dbplyr)
library(sqlpetr)
```


Verify Docker is up and running:
```{r}
sp_check_that_docker_is_up()
```

Verify pet DB is available, it may be stopped.

```{r}
sp_show_all_docker_containers()
```

Start up the `docker-pet` container

```{r}
sp_docker_start("sql-pet")
```

Now connect to the database with R

```{r}
# need to wait for Docker & Postgres to come up before connecting.

con <- sp_get_postgres_connection(
  user = Sys.getenv("DEFAULT_POSTGRES_USER_NAME"),
  password = Sys.getenv("DEFAULT_POSTGRES_PASSWORD"),
  dbname = "dvdrental",
  seconds_to_test = 30, connection_tab = TRUE
)
```

```{r collapse=TRUE}
source(file=here('book-src/sql_pet_data.R'),echo=TRUE)
```

Explain plans [here](https://robots.thoughtbot.com/reading-an-explain-analyze-query-plan)

## SQL anti join Costs

```{r}
sql_aj1 <- dbGetQuery(
  con,
  "explain analyze
   select 'aj' join_type, customer_id, first_name, last_name, c.store_id,count(*) ajs
   from customer c left outer join store s on c.store_id = s.store_id
  where s.store_id is null
  group by customer_id, first_name, last_name, c.store_id
order by c.customer_id;"
)

sql_aj2 <- dbGetQuery(
  con,
  "explain analyze
   select 'aj' join_type, customer_id, first_name, last_name, c.store_id,count(*) ajs
   from customer c 
  where c.store_id NOT IN (select store_id from store)
  group by  customer_id, first_name, last_name, c.store_id
order by c.customer_id;"
)

sql_aj3 <- dbGetQuery(
  con,
  "explain analyze
   select 'aj' join_type, customer_id, first_name, last_name, c.store_id,count(*) ajs
   from customer c 
  where not exists (select s.store_id from store s where s.store_id = c.store_id)
 group by customer_id, first_name, last_name, c.store_id
order by c.customer_id
"
)
```

##### SQL Costs

```{r}
print(glue("sql_aj1 loj-null costs=", sql_aj1[1, 1]))
print(glue("sql_aj2 not in costs=", sql_aj2[1, 1]))
print(glue("sql_aj3 not exist costs=", sql_aj3[1, 1]))
```

## dplyr Anti joins  

In this next section we look at two methods to implemnt an anti join in dplyr.

```{r}
customer_table <- tbl(con, "customer") # DBI::dbReadTable(con, "customer")
rental_table <- tbl(con, "rental") # DBI::dbReadTable(con, "rental")

# Method 1.  dplyr anti_join
daj1 <-
  anti_join(customer_table, rental_table, by = "customer_id", suffix = c(".c", ".r")) %>%
  select(c("first_name", "last_name", "email")) %>%
  explain()
```

```{r}
customer_table <- tbl(con, "customer") # DBI::dbReadTable(con, "customer")
rental_table <- tbl(con, "rental") # DBI::dbReadTable(con, "rental")

# Method 2.  dplyr loj with NA
daj2 <-
  left_join(customer_table, rental_table, by = c("customer_id", "customer_id"), suffix = c(".c", ".r")) %>%
  filter(is.na(rental_id)) %>%
  select(c("first_name", "last_name", "email")) %>%
  explain()
```

<!-- 


### dplyr Costs

```
<PLAN>
Hash Anti Join  (cost=510.99..529.72 rows=1 width=45)
  Hash Cond: ("TBL_LEFT".customer_id = "TBL_RIGHT".customer_id)
  ->  Seq Scan on customer "TBL_LEFT"  (cost=0.00..14.99 rows=599 width=49)
  ->  Hash  (cost=310.44..310.44 rows=16044 width=2)
        ->  Seq Scan on rental "TBL_RIGHT"  (cost=0.00..310.44 rows=16044 width=2)
```

```
<PLAN>
Hash Right Join  (cost=22.48..375.33 rows=1 width=45)
  Hash Cond: ("TBL_RIGHT".customer_id = "TBL_LEFT".customer_id)
  Filter: ("TBL_RIGHT".rental_id IS NULL)
  ->  Seq Scan on rental "TBL_RIGHT"  (cost=0.00..310.44 rows=16044 width=6)
  ->  Hash  (cost=14.99..14.99 rows=599 width=49)
        ->  Seq Scan on customer "TBL_LEFT"  (cost=0.00..14.99 rows=599 width=49)
```
-->


In this example, the dplyr anti_join verb is *`r 529.72/375.33` to `r 510.99/22.48`* times more expensive than the left outer join with a null condition.


```{r}
sql_aj1 <- dbGetQuery(
  con,
  "explain analyze select c.customer_id,count(*) lojs
   from customer c left outer join rental r on c.customer_id = r.customer_id
  where r.customer_id is null
  group by c.customer_id
order by c.customer_id;"
)
sp_print_df(sql_aj1)
sql_aj1

sql_aj3 <- dbGetQuery(
  con,
  "explain analyze 
select c.customer_id,count(*) lojs
   from customer c 
  where not exists (select customer_id from rental r where c.customer_id = r.customer_id)
 group by c.customer_id
"
)

print(glue("sql_aj1 loj-null costs=", sql_aj1[1, 1]))
print(glue("sql_aj3 not exist costs=", sql_aj3[1, 1]))
```
## Cleaning up

Always have R disconnect from the database when you're done and stop the Adventureworks Container
```{r}

dbDisconnect(con)
sp_docker_stop("adventureworks")

```