Add Concatenate Strings With A Separator as a Postgres TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1485 TILs and counting..._
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@@ -723,6 +723,7 @@ _1485 TILs and counting..._
 - [Compute Hashes With pgcrypto](postgres/compute-hashes-with-pgcrypto.md)
 - [Compute The Levenshtein Distance Of Two Strings](postgres/compute-the-levenshtein-distance-of-two-strings.md)
 - [Compute The md5 Hash Of A String](postgres/compute-the-md5-hash-of-a-string.md)
+- [Concatenate Strings With A Separator](postgres/concatenate-strings-with-a-separator.md)
 - [Configure The Timezone](postgres/configure-the-timezone.md)
 - [Constructing A Range Of Dates](postgres/constructing-a-range-of-dates.md)
 - [Convert A String To A Timestamp](postgres/convert-a-string-to-a-timestamp.md)

postgres/concatenate-strings-with-a-separator.md

@@ -0,0 +1,41 @@
+# Concatenate Strings With A Separator
+
+I was putting together an example of using a generated column that concatenates
+string values from a few other columns. I used manual concatenation with the
+`||` operator like so:
+
+```sql
+create table folders (
+  id integer generated always as identity primary key,
+  user_id integer not null,
+  name text not null,
+  parent_folder_id integer references folders(id),
+  path text generated always as (
+    user_id::text || ':' || lower(name) || ':' || coalesce(parent_folder_id::text, '0')
+  ) stored
+);
+```
+
+Instead of doing that manual concatenation for the `path` generated column, I
+can use
+[`concat_ws`](https://www.postgresql.org/docs/current/functions-string.html).
+
+```sql
+create table folders (
+  id integer generated always as identity primary key,
+  user_id integer not null,
+  name text not null,
+  parent_folder_id integer references folders(id),
+  path text generated always as (
+    concat_ws(
+      ':',
+      user_id::text,
+      lower(name),
+      coalesce(parent_folder_id::text, '0')
+    )
+  ) stored
+);
+```
+
+The first argument to `concat_ws` is the separator I want to use. The remaining
+arguments are the strings that should be concatenated with that separator.