Oracle SQL to find tables hierarchy in a schema - sql

Question

I have a need to import some data for a given input from multiple table's and schema's based on a key.
For-Ex: I have ACCOUNT_ID COLUMN which is common to multiple tables (tables are interdependent with FK). I want to import data for a specific account from all the tables from multiple schema's and generate a SQL script.
But the challenge is, I need to identify parent table's first and then their child table's (tied with FK) in the order so that when I run the script, it shouldn't error out with integrity violation errors.
One way is to disable all the constraints, generate the script, run and then enable the constraints.
But I am trying to find if there's a better way of doing this. And enabling/disabling the constraints may not be a good solution for me.
Appreciate any inputs on this issue.

Answer 1

You say that your tables create a hierarchy based on foreign keys, so that for example T1 references T2, and T2 references T3 and so on.
In this case you need a hierarchical query.
First create a view that shows references between tables:
select c.table_name, uc.table_name as referenced_table_name
from user_constraints c
join USER_CONS_columns uc ON c.r_constraint_name = uc.constraint_name
where c.constraint_type = 'R'
For example in this case:
CREATE TABLE ttt1(
ACCOUNT_ID int primary key,
somecolumn varchar2(100)
);
CREATE TABLE ttt21(
id int primary key,
ACCOUNT_ID int referencing ttt1( ACCOUNT_ID ),
somecolumn varchar2(100)
);
CREATE TABLE ttt22(
id int primary key,
ACCOUNT_ID int referencing ttt1( ACCOUNT_ID ),
somecolumn varchar2(100)
);
CREATE TABLE ttt211(
id int primary key,
ACCOUNT_ID int referencing ttt21( id ),
somecolumn varchar2(100)
);
CREATE TABLE ttt2111(
id int primary key,
ACCOUNT_ID int referencing ttt211( id ),
somecolumn varchar2(100)
);
CREATE TABLE ttt2112(
id int primary key,
ACCOUNT_ID int referencing ttt211( id ),
somecolumn varchar2(100)
);
the view gives:
TABLE_NAME REFERENCED_TABLE_NAME
---------- -------------------------
TTT22 TTT1
TTT211 TTT21
TTT21 TTT1
TTT2111 TTT211
TTT2112 TTT211
And now, with the help of this view, you can create a hierarchical query:
WITH my_view AS(
select c.table_name, uc.table_name as referenced_table_name
from user_constraints c
join USER_CONS_columns uc ON c.r_constraint_name = uc.constraint_name
where c.constraint_type = 'R'
) SELECT level, m.referenced_table_name
FROM my_view m
START WITH referenced_table_name not in (select table_name from my_view )
CONNECT BY prior table_name = referenced_table_name;
which gives the following output:
LEVEL REFERENCED_TABLE_NAME
---------- -------------------------
1 TTT1
2 TTT21
3 TTT211
3 TTT211
1 TTT1
A LEVEL column gives an order in which tables must be imported - first you need to process all tables at level 1, then at level 2 and so on and so on.