Add Prepare, Execute, and Deallocate Statements as a postgres til

postgres/prepare-execute-and-deallocate-statements.md

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+# Prepare, Execute, and Deallocate Statements
+
+In PostgreSQL, you can prepare a named statement to be executed later using
+[`prepare`](https://www.postgresql.org/docs/current/static/sql-prepare.html).
+
+```sql
+> prepare column_names (text) as  select column_name from information_schema.columns where table_name = $1;
+PREPARE
+```
+
+These statements are kept around for the duration of the session. To see the
+available statements, check out the `pg_prepared_statements` view.
+
+```sql
+> select * from pg_prepared_statements;
+     name     |                                  statement                                  |         prepare_time          | parameter_types | from_sql
+--------------+-----------------------------------------------------------------------------+-------------------------------+-----------------+----------
+ column_names | prepare column_names (text) as                                             +| 2017-03-10 15:01:09.154528-06 | {text}          | t
+              |   select column_name from information_schema.columns where table_name = $1; |                               |                 |
+```
+
+To run a prepared statement, use `execute` with the name of the statement
+and any arguments.
+
+```sql
+> execute column_names('users');
+   column_name
+-----------------
+ id
+ email
+ password_digest
+ created_at
+ updated_at
+ first_name
+ last_name
+```
+
+You can also delete a statement with
+[`deallocate`](https://www.postgresql.org/docs/current/static/sql-deallocate.html)
+if you'd like.
+
+```sql
+> deallocate column_names;
+DEALLOCATE
+```