Postgres 15

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select version();

version

PostgreSQL 15beta3 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-10), 64-bit

SELECT 1

CREATE TABLE foo (
    id INT PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
    name TEXT DEFAULT md5(random()::text)
);

CREATE TABLE

insert into foo (id)
  OVERRIDING USER VALUE
select null
from generate_series(1, 3) as gs(i) ;   -- add 3 rows

select * from foo ;

INSERT 0 3

id
name

1
302e3ff639345fc7c518dcd1b0f582d3

2
efb27034dab7993125841fd5c24d4897

3
ccd0f401e352541b16785c9b47fd9264

SELECT 3

MERGE INTO
  foo AS tgt
USING
  generate_series(1, 5) AS src   -- add 5 more rows
ON
  FALSE
WHEN NOT MATCHED THEN
  INSERT DEFAULT VALUES ;

select * from foo ;

MERGE 5

id
name

1
302e3ff639345fc7c518dcd1b0f582d3

2
efb27034dab7993125841fd5c24d4897

3
ccd0f401e352541b16785c9b47fd9264

4
eee08eff992da75e0c132eb597a1bc9c

5
cf6fadab281f9eb9de4b27e89710ac6c

6
b8051b666f7a5ccfd1fbc67831498f77

7
baa38d6950fe1a29729f3089568b3342

8
bbf8fa4277fe11feb335028df578850e

SELECT 8

MERGE INTO
  foo AS tgt
USING
  generate_series(1, 5) AS src   -- add 5 more rows
ON
  FALSE
WHEN NOT MATCHED THEN   
  INSERT (id) VALUES (DEFAULT);

select * from foo ;

MERGE 5

id
name

1
302e3ff639345fc7c518dcd1b0f582d3

2
efb27034dab7993125841fd5c24d4897

3
ccd0f401e352541b16785c9b47fd9264

4
eee08eff992da75e0c132eb597a1bc9c

5
cf6fadab281f9eb9de4b27e89710ac6c

6
b8051b666f7a5ccfd1fbc67831498f77

7
baa38d6950fe1a29729f3089568b3342

8
bbf8fa4277fe11feb335028df578850e

9
ff3139194daced847bae2b5199204c43

10
29885d25541bdd061c32517cbeef49dd

11
af0d4959b0f6098cbff5fedc17cbd646

12
db377312ebb33fed5526fb9fc54813c5

13
62c8baecff14e5532fd4b0e7d61051d6

SELECT 13

insert into foo
select
from generate_series(1, 2) as gs(i) ;

select * from foo ;

INSERT 0 2

id
name

1
302e3ff639345fc7c518dcd1b0f582d3

2
efb27034dab7993125841fd5c24d4897

3
ccd0f401e352541b16785c9b47fd9264

4
eee08eff992da75e0c132eb597a1bc9c

5
cf6fadab281f9eb9de4b27e89710ac6c

6
b8051b666f7a5ccfd1fbc67831498f77

7
baa38d6950fe1a29729f3089568b3342

8
bbf8fa4277fe11feb335028df578850e

9
ff3139194daced847bae2b5199204c43

10
29885d25541bdd061c32517cbeef49dd

11
af0d4959b0f6098cbff5fedc17cbd646

12
db377312ebb33fed5526fb9fc54813c5

13
62c8baecff14e5532fd4b0e7d61051d6

14
821475a44d81fd9abdfac37d1e3a0e1a

15
53e44cf5fdc7fd0cfdf7978619d11be5

SELECT 15
id	name
1	302e3ff639345fc7c518dcd1b0f582d3
2	efb27034dab7993125841fd5c24d4897
3	ccd0f401e352541b16785c9b47fd9264