【PostgreSQL】psqlのクエリバッファをg系メタコマンドで活用する

testdb=# SELECT id, name FROM users WHERE id = 1
testdb-# \g
 id | name
----+-------
  1 | alice
(1 row)

testdb=# SELECT * FROM users LIMIT 1;
 id | name  |       email
----+-------+-------------------
  1 | alice | alice@example.com
(1 row)

testdb=# \g /tmp/result.txt

$ cat /tmp/result.txt
 id | name  |       email
----+-------+-------------------
  1 | alice | alice@example.com
(1 row)

testdb=# SELECT id, name FROM users WHERE id = 1
testdb-# \gx
-[ RECORD 1 ]
id   | 1
name | alice

testdb=# SELECT * FROM users LIMIT 1
testdb-# \gdesc
 Column |  Type
--------+---------
 id     | integer
 name   | text
 email  | text
(3 rows)

testdb=# SELECT count(*) AS user_count, max(id) AS max_id FROM users;
testdb=# \gset
testdb=# \echo :user_count
2
testdb=# \echo :max_id
2

testdb=# SELECT * FROM users WHERE id = :max_id;
 id | name |      email
----+------+-----------------
  2 | bob  | bob@example.com
(1 row)

testdb=# SELECT count(*) AS cnt FROM users;
testdb=# \gset user_
testdb=# \echo :user_cnt
2

testdb=# SELECT 'SELECT count(*) FROM ' || tablename || ';'
testdb-# FROM pg_tables
testdb-# WHERE schemaname = 'public' AND tablename IN ('users', 'orders');
         ?column?
------------------------------
 SELECT count(*) FROM orders;
 SELECT count(*) FROM users;
(2 rows)

testdb=# \gexec
 count
-------
     3
(1 row)

 count
-------
     2
(1 row)