Add Concatenate Strings With A Separator as a Postgres TIL

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

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+# 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.