Adding ' notation' and 'Executing multiple statements' sub-sections.

README.md

@@ -170,6 +170,42 @@ $ migrate -source="github://user:personal-access-token@owner/repo/path#ref" -dat
 
 More information about this functionality and a full list of the supported remote resources can be [found here](https://github.com/golang-migrate/migrate#migration-sources).
 
+### $N notation
+
+A nice feature of the PostgreSQL placeholder parameter **$N** notation is that you can use the same parameter value in multiple places in your SQL statement. For example, it's perfectly acceptable to write code like :
+
+```go
+// This SQL statement uses the $1 parameter twice, and the value `123` will be used in both locations where $1 appears
+stmt := "UPDATE foo SET bar = $1 + $2 WHERE bar = $1"
+err := db.Exec(stmt, 123, 456)
+if err != nil {
+	// ...
+}
+```
+
+### Executing multiple statements
+
+Occasionally, you might find yourself in the position where you want to execute more than one SQL statement in the same database call, like this :
+
+```go
+stmt := `
+    UPDATE foo SET bar = true;
+    UPDATE foo SET bar = false;`
+
+err := db.Exec(stmt)
+if err != nil {
+	// ...
+}
+```
+
+Having multiple statements in the same call is supported by the **pq** driver, so long as the statements do not contain any placeholder parameters. If they do contain placeholder parameters, then you'll receive the following error message at runtime:
+
+```bash
+pq: cannot insert multiple commands into a prepared statement
+```
+
+To work around this, you will need to either split out the statements into separate database calls, or if that's not possible, you can create a [custom function](https://www.postgresql.org/docs/current/xfunc-sql.html) in PostgreSQL which acts as a wrapper around the multiple SQL statements that you want to run.
+
 ## Additional Information
 
 ### How different Go Types are encoded