How to insert long-format data into two separate tables using SQL? - sql

Question

I have selected the following data that I want to insert into the database.
Letter
Value
A
1
A
2
B
3
B
4
Since there is a repetition of "A" and "B" in this format, I want to split data into two separate tables: table1 and table2.
table1:
ID
Letter
1
A
2
B
ID here is automatically inserted by database (using a sequence).
table2:
table1_id
Value
1
1
1
2
2
3
2
4
In this particular example, I don't gain anything on storage but it illustrates in the best way what problem I have encountered.
How can I use SQL or PL/SQL to insert data into table1 and table2?

Answer 1

First populate table1 from the source
insert table1(Letter)
select distinct Letter
from srcTable;
Then load data from the source decoding letter to id
insert table2(table1_id, Value)
select t1.id, src.value
from srcTable src
join table1 t1 on t1.Letter = src.Letter;

Answer 2

You may use multitable insert with workaround to get stable nextval on sequence. Since nextval is evaluated on each row regardless of when condition, it is not sufficient to use it inside values.
insert all
when rn = 1 then into l(id, val) values(seq, letter)
when rn > 0 then into t(l_id, val) values(seq, val)
with a(letter, val) as (
select 'A', 1 from dual union all
select 'A', 2 from dual union all
select 'B', 3 from dual union all
select 'B', 4 from dual union all
select 'C', 5 from dual
)
, b as (
select
a.*,
l.id as l_id,
row_number() over(partition by a.letter order by a.val asc) as rn
from a
left join l
on a.letter = l.val
)
select
b.*,
max(decode(rn, 1, coalesce(
l_id,
extractvalue(
/*Hide the reference to the sequence due to restrictions
of multitalbe insert*/
dbms_xmlgen.getxmltype('select l_sq.nextval as seq from dual')
, '/ROWSET/ROW/SEQ/text()'
) + 0
))
) over(partition by b.letter) as seq
from b
select *
from l
ID | VAL
-: | :--
1 | A
2 | B
3 | C
select *
from t
L_ID | VAL
---: | --:
1 | 1
1 | 2
2 | 3
2 | 4
3 | 5
db<>fiddle here

Answer 3

Principally you need to produce and ID value for the table1 to be inserted into table2. For this, You can use INSERT ... RETURNING ID INTO v_id statement after creating the tables containing some constraints especially unique ones such as PRIMARY KEY and UNIQUE
CREATE TABLE table1( ID INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY, letter VARCHAR2(1) NOT NULL );
ALTER TABLE table1 ADD CONSTRAINT uk_tab1_letter UNIQUE(letter);
CREATE TABLE table2( ID INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY, table1_id INT, value INT );
ALTER TABLE table2 ADD CONSTRAINT fk_tab2_tab1_id FOREIGN KEY(table1_id) REFERENCES table1 (ID);
and adding exception handling in order not to insert repeating letters to the first table. Then use the following code block ;
DECLARE
v_id table1.id%TYPE;
v_letter table1.letter%TYPE := 'A';
v_value table2.value%TYPE := 1;
BEGIN
BEGIN
INSERT INTO table1(letter) VALUES(v_letter) RETURNING ID INTO v_id;
EXCEPTION WHEN OTHERS THEN NULL;
END;
INSERT INTO table2(table1_id,value) SELECT id,v_value FROM table1 WHERE letter = v_letter;
COMMIT;
END;
/
and run by changing the initialized values for v_letter&v_value as 'A'&2, 'B'&1,'B'&2 ..etc respectively.
Alternatively you can convert the code block to a stored procedure or function such as
CREATE OR REPLACE PROCEDURE Pr_Ins_Tabs(
v_letter table1.letter%TYPE,
v_value table2.value%TYPE
) AS
v_id table1.id%TYPE;
BEGIN
BEGIN
INSERT INTO table1(letter) VALUES(v_letter) RETURNING ID INTO v_id;
EXCEPTION WHEN OTHERS THEN NULL;
END;
INSERT INTO table2(table1_id,value) SELECT id,v_value FROM table1 WHERE letter = v_letter;
COMMIT;
END;
/
in order to revoke resiliently such as
BEGIN
Pr_Ins_Tabs('A',2);
END;
/
Demo
PS. If your DB verion is prior to 12c, then create sequences(seq1&seq2) and use seq1.nextval&seq2.nextval within the Insert statements as not possible to use GENERATED ALWAYS AS IDENTITY clause within the table creation DDL statements.