From 48d2ecffa048fcf213378fcdb8f56dd34b7afad1 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Thu, 16 May 2024 14:49:37 -0500
Subject: [PATCH] Add Get Row Count For Most Recent Query as a Postgres TIL

---
 README.md                                     |  3 +-
 .../get-row-count-for-most-recent-query.md    | 63 +++++++++++++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)
 create mode 100644 postgres/get-row-count-for-most-recent-query.md

diff --git a/README.md b/README.md
index e05ab4a..2d75177 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1430 TILs and counting..._
+_1431 TILs and counting..._
 
 ---
 
@@ -734,6 +734,7 @@ _1430 TILs and counting..._
 - [Generate Series Of Numbers](postgres/generate-series-of-numbers.md)
 - [Generating UUIDs With pgcrypto](postgres/generating-uuids-with-pgcrypto.md)
 - [Get A Quick Approximate Count Of A Table](postgres/get-a-quick-approximate-count-of-a-table.md)
+- [Get Row Count For Most Recent Query](postgres/get-row-count-for-most-recent-query.md)
 - [Get The Size On Disk of An Index](postgres/get-the-size-on-disk-of-an-index.md)
 - [Get The Size Of A Database](postgres/get-the-size-of-a-database.md)
 - [Get The Size Of A Table](postgres/get-the-size-of-a-table.md)
diff --git a/postgres/get-row-count-for-most-recent-query.md b/postgres/get-row-count-for-most-recent-query.md
new file mode 100644
index 0000000..6f11000
--- /dev/null
+++ b/postgres/get-row-count-for-most-recent-query.md
@@ -0,0 +1,63 @@
+# Get Row Count For Most Recent Query
+
+Anytime you execute a query in `psql`, there is a _row count_ associated with
+that query. This is most naturally understood with a `select` query where a
+discreet number of rows are returned. We typically see the row count (e.g. `(19
+rows)`) right below the result set.
+
+You can always reference the row count of the most recent query with [the
+`:ROW_COUNT`
+variable](https://www.postgresql.org/docs/current/app-psql.html#APP-PSQL-VARIABLES-ROW-COUNT).
+Here we use `\echo` to print it out.
+
+```sql
+> select generate_series(2,20);
+ generate_series
+-----------------
+               2
+               3
+               4
+               5
+               6
+               7
+               8
+               9
+              10
+              11
+              12
+              13
+              14
+              15
+              16
+              17
+              18
+              19
+              20
+(19 rows)
+
+Time: 12.338 ms
+> \echo :ROW_COUNT
+19
+```
+
+For some queries, like one that induces a pager (e.g. `less`) to be used,
+you'll lose track of the row count once the pager closes. This is where being
+able to reference the row count without rerunning the query is most useful.
+
+```sql
+> select generate_series(2,2000);
+Time: 9.815 ms
+> \echo :ROW_COUNT
+1999
+```
+
+Notice, we can also get a row count from other kinds of queries like this
+`insert` statement.
+
+```sql
+> insert into users (id) values (50001), (50002), (50003);
+INSERT 0 3
+Time: 2.804 ms
+> \echo :ROW_COUNT
+3
+```