Postgres Insert N Rows in a Loop for All Values in a Selected Column

Question

Suppose I have users stored as

select * from users_t where user_name like 'ABC%';

id   user_name  
1    ABC1
2    ABC2
..   ..

Now I need to loop through all user_name's and make that number of INSERTs into a different table, RECALLS_T. All the other columns are hard-coded constants that I define.

Assume the following table, with a Sequence called RECALLS_T_ID_SEQ on the ID:

id  created_by_user_name  field1   field2
1   ABC1                  Const1   Const2
2   ABC2                  Const1   Const2
..   ..                   ..       ..

How do I insert these in a Postgres loop?

ADDITIONAL QUESTION Also, what if I need to insert X (say 5) Recalls for each User entry? Suppose it's not a 1:1 mapping, but 5:1, where 5 is a hard-coded loop number.

klin · Accepted Answer · 2019-10-23 20:39:12Z

3

You can use the select in the insert statement:

insert into recalls_t (created_by_user_name, field1, field2)
select user_name, 'Const1', 'Const2'
from users_t 
where user_name like 'ABC%';

Use the function generate_series() to insert more than one row for each entry from users_t. I have added the column step to illustrate this:

insert into recalls_t (created_by_user_name, field1, field2, step)
select user_name, 'Const1', 'Const2', step
from users_t 
cross join generate_series(1, 3) as step
where user_name like 'ABC%'
returning *

 id | created_by_user_name | field1 | field2 | step 
----+----------------------+--------+--------+------
  1 | ABC1                 | Const1 | Const2 |    1
  2 | ABC2                 | Const1 | Const2 |    1
  3 | ABC1                 | Const1 | Const2 |    2
  4 | ABC2                 | Const1 | Const2 |    2
  5 | ABC1                 | Const1 | Const2 |    3
  6 | ABC2                 | Const1 | Const2 |    3
(6 rows)

Live demo in Db<>fiddle.

edited Oct 23, 2019 at 20:39

answered Oct 22, 2019 at 18:43

klin

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1 Comment

gene b. Over a year ago

Thanks; also, what if I need to insert X (say 5) Recalls for each User entry? Suppose it's not a 1:1 mapping, but 5:1, where 5 is a hard-coded loop number.

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