Add note that IMPORT INTO invalidates FKs

Closes cockroachdb#7278.

Author: Lauren

v19.2/import-into.md

@@ -10,6 +10,7 @@ toc: true
 
 - `IMPORT INTO` only works for existing tables. For information on how to import data into new tables, see [`IMPORT`](import.html).
 - `IMPORT INTO` cannot be used within a [transaction](transactions.html) or during a [rolling upgrade](upgrade-cockroach-version.html).
+- `IMPORT INTO` invalidates all [foreign keys](foreign-key) on the target table. To validate the foreign key(s), use the [`VALIDATE CONSTRAINT`](validate-constraint.html) statement.
 - `IMPORT INTO` cannot be used to insert data into a column for an existing row. To do this, use [`INSERT`](insert.html).
 
 ## Required privileges

v20.1/import-into.md

@@ -10,6 +10,7 @@ The `IMPORT INTO` [statement](sql-statements.html) imports CSV data into an [exi
 
 - `IMPORT INTO` only works for existing tables. For information on how to import data into new tables, see [`IMPORT`](import.html).
 - `IMPORT INTO` cannot be used within a [transaction](transactions.html) or during a [rolling upgrade](upgrade-cockroach-version.html).
+- `IMPORT INTO` invalidates all [foreign keys](foreign-key) on the target table. To validate the foreign key(s), use the [`VALIDATE CONSTRAINT`](validate-constraint.html) statement.
 - `IMPORT INTO` cannot be used to insert data into a column for an existing row. To do this, use [`INSERT`](insert.html).
 
 ## Required privileges

v20.2/import-into.md

@@ -10,9 +10,9 @@ The `IMPORT INTO` [statement](sql-statements.html) imports CSV data into an [exi
 
 - `IMPORT INTO` only works for existing tables. For information on how to import data into new tables, see [`IMPORT`](import.html).
 - `IMPORT INTO` cannot be used within a [transaction](transactions.html) or during a [rolling upgrade](upgrade-cockroach-version.html).
+- `IMPORT INTO` invalidates all [foreign keys](foreign-key) on the target table. To validate the foreign key(s), use the [`VALIDATE CONSTRAINT`](validate-constraint.html) statement.
 - `IMPORT INTO` cannot be used to insert data into a column for an existing row. To do this, use [`INSERT`](insert.html).
 
-
 ## Required privileges
 
 Only members of the `admin` role can run `IMPORT INTO`. By default, the `root` user belongs to the `admin` role.