Add Label Dollar-Quoted Strings With A Tag as a Postgres TIL

postgres/label-dollar-quoted-strings-with-a-tag.md

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+# Label Dollar-Quoted Strings With A Tag
+
+In [Escaping String Literals with Dollar
+Quoting](escaping-string-literals-with-dollar-quoting.md), I showed how
+PostgreSQL supports escaped string literals so that you don't have to put
+backslashes everywhere. This is done by opening and closing the string with
+`$$`.
+
+What if your string literal is going to contain a sequence of two `$` symbols?
+Or a better hypothetical, what if you want to convey some information about
+what the string represents?
+
+For either of these, the _tagged_ dollar-quoting is a great fit.
+
+```sql
+> select $JSON${"name": "Sally's Bistro", "price": "$$$"}$JSON$::jsonb;
+                   jsonb
+--------------------------------------------
+ {"name": "Sally's Bistro", "price": "$$$"}
+(1 row)
+
+> select $JSON${"name": "Sally's Bistro", "price": "$$$"}$JSON$::jsonb->'name' as name;
+       name
+------------------
+ "Sally's Bistro"
+(1 row)
+```
+
+The tagged dollar-quoting allows me to write a string that can be cast to
+`jsonb` without having to think about which characters need to be escaped. In
+the second example, I'm able to interact with it like any `jsonb` entity.
+
+Here, our tag is `JSON`. It helps convey that the string literal represents
+JSON. A tag "follows the same rules as an unquoted identifier, except that it
+cannot contain a dollar sign." The tag goes between the dollar signs and is
+case-sensitive.
+
+[source](https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING)