PostgreSQL and sequence

psql_sequence.sql

# Create test table
CREATE TABLE mytable (
	id bigint not null generated by default as identity primary key,
	value1 varchar,
	value2 varchar
);

# Add data (bad!)
INSERT INTO mytable(id, value1, value2) VALUES
(1,'Daniele','Teti'),
(2,'Peter','Parker'),
(3,'Bruce','Banner');

# Add data (valid)
INSERT INTO mytable(value1, value2)	 VALUES ('Jake', 'The Cat');
# but error
# ERROR:  duplicate key value violates unique constraint "mytable_pkey"
# DETAIL:  Key (id)=(1) already exists.

# Get last max id
WITH test1 AS (
SELECT id AS last_value_order FROM public.mytable ORDER BY id DESC LIMIT 1
), test2 AS (
SELECT last_value AS last_value_seq FROM public.mytable_id_seq
), test3 AS (
SELECT max(id) AS last_value_max FROM public.mytable
) SELECT last_value_order, last_value_seq, last_value_max FROM test1, test2, test3;

# Result
+------------------+----------------+----------------+
| last_value_order | last_value_seq | last_value_max |
+------------------+----------------+----------------+
|                3 |              1 |              3 |
+------------------+----------------+----------------+
(1 row)

# last_value_seq <> last_value_order and last_value_max

# Fixed
SELECT 
	'SELECT setval(pg_get_serial_sequence(''' 
        || pg_class.relname || ''',''' || attname || '''), (SELECT max(' 
        || attname || ') FROM ' || pg_class.relname || '));' sql_stm
FROM 
	pg_attribute JOIN pg_class ON pg_attribute.attrelid = pg_class.oid 
WHERE 
	attnum > 0 and attidentity = 'd' AND pg_class.relname = 'mytable';

# Exec
SELECT setval(pg_get_serial_sequence('mytable','id'), (SELECT max(id) FROM mytable));

# Get last max id
WITH test1 AS (
SELECT id AS last_value_order FROM public.mytable ORDER BY id DESC LIMIT 1
), test2 AS (
SELECT last_value AS last_value_seq FROM public.mytable_id_seq
), test3 AS (
SELECT max(id) AS last_value_max FROM public.mytable
) SELECT last_value_order, last_value_seq, last_value_max FROM test1, test2, test3;

# Result
+------------------+----------------+----------------+
| last_value_order | last_value_seq | last_value_max |
+------------------+----------------+----------------+
|                3 |              3 |              3 |
+------------------+----------------+----------------+

# Good!

# Get next id
SELECT last_value + CASE WHEN is_called THEN 1 ELSE 0 END AS next_id FROM public.mytable_id_seq;

# Result
+---------+
| next_id |
+---------+
|       4 |
+---------+

# Select all data
SELECT * FROM public.mytable;
+----+---------+--------+
| id | value1  | value2 |
+----+---------+--------+
|  1 | Daniele | Teti   |
|  2 | Peter   | Parker |
|  3 | Bruce   | Banner |
+----+---------+--------+
(3 rows)

# Add 1 row
INSERT INTO mytable(value1, value2)	 VALUES ('Jake', 'The Cat');

# Good

# Select all data
SELECT * FROM public.mytable;
+----+---------+---------+
| id | value1  | value2  |
+----+---------+---------+
|  1 | Daniele | Teti    |
|  2 | Peter   | Parker  |
|  3 | Bruce   | Banner  |
|  4 | Jake    | The Cat |
+----+---------+---------+
(4 rows)

# Get last max id
WITH test1 AS (
SELECT id AS last_value_order FROM public.mytable ORDER BY id DESC LIMIT 1
), test2 AS (
SELECT last_value AS last_value_seq FROM public.mytable_id_seq
), test3 AS (
SELECT max(id) AS last_value_max FROM public.mytable
) SELECT last_value_order, last_value_seq, last_value_max FROM test1, test2, test3;

# Result
+------------------+----------------+----------------+
| last_value_order | last_value_seq | last_value_max |
+------------------+----------------+----------------+
|                4 |              4 |              4 |
+------------------+----------------+----------------+

# Good and bye!