Can Oracle's CTAs bring constraints and other attributes to the new table?

I saw a question today , These mentioned functional attributes are familiar , But just ask , It's a little vague , Practice is the only criterion for testing truth , Only through experiments , To prove our guess ,

Translate the question , What we want to verify is , The primary key on a table 、 Unique constraint 、NOT NULL constraint 、 Foreign key constraints , When in Oracle Pass through CTAS Will a new table be copied when it is created ？

Create test table ,

CREATE TABLE t1(id NUMBER PRIMARY KEY, c1 varchar2(1) NOT NULL, c2 NUMBER, c3 NUMBER UNIQUE);
CREATE TABLE t2(id NUMBER PRIMARY KEY, c1 varchar2(1) NOT NULL);
ALTER TABLE t1 ADD CONSTRAINT fk_t1_t2 FOREIGN KEY (c2) REFERENCES t2(id);

id It's the primary key column ,c1 There is NOT NULL constraint ,c2 There are foreign key constraints ,c3 There is a unique constraint , There is a DBeaver The display problem of the database client , Table constraints 、 In the foreign key view , Are not displayed c2 This foreign key constraint ,

But through the view user_constraints, You can find the created foreign key constraint ,

SQL> exec print_table('select constraint_name, constraint_type from user_constraints where table_name=''T1''');
CONSTRAINT_NAME : FK_T1_T2
CONSTRAINT_TYPE : R
-----------------
CONSTRAINT_NAME : SYS_C007441
CONSTRAINT_TYPE : C
-----------------
CONSTRAINT_NAME : SYS_C007442
CONSTRAINT_TYPE : P
-----------------
CONSTRAINT_NAME : SYS_C007443
CONSTRAINT_TYPE : U
-----------------


PL/SQL procedure successfully completed.

CTAS Create table ,

CREATE TABLE t1_1 AS SELECT * FROM t1;

You can see , The new table only has this non empty constraint , Primary key 、 Unique constraint 、 Foreign key constraints , I didn't bring it with me ,

SQL> exec print_table('select constraint_name, constraint_type, search_condition from user_constraints where table_name=''T1_1''');
CONSTRAINT_NAME : SYS_C007445
CONSTRAINT_TYPE : C
SEARCH_CONDITION : "C1" IS NOT NULL
-----------------


PL/SQL procedure successfully completed.

therefore , The answer is obvious .

however , Why is this phenomenon ？ We from Oracle The official manual , Can see some clues ,《SQL Language Reference》 When it comes to the CTAS The ability to replicate constraints , In addition to the constraint types involved in the above experiments , Other properties that cannot be copied , Are explained here ,

https://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_7002.htm#sthref5328

Oracle Database derives data types and lengths from the subquery. Oracle Database follows the following rules for integrity constraints and other column and table attributes:

> Oracle Database automatically defines on columns in the new table any NOT NULL constraints that have a state of NOT DEFERRABLE and VALIDATE, and were explicitly created on the corresponding columns of the selected table if the subquery selects the column rather than an expression containing the column. If any rows vio‍late the constraint, then the database does not create the table and returns an error.

Explicit NOT NULL Constraints are automatically brought to the new table .

> NOT NULL constraints that were implicitly created by Oracle Database on columns of the selected table (for example, for primary keys) are not carried over to the new table.

implicit NOT NULL Constraints will not be brought to the new table , For example, a primary key .

> In addition, primary keys, unique keys, foreign keys, check constraints, partitioning criteria, indexes, and column default values are not carried over to the new table.

in addition , Primary key , only , Foreign keys ,check constraint , Partition , The default values of indexes and columns will not be brought to the new table .

> If the selected table is partitioned, then you can choose whether the new table will be partitioned the same way, partitioned differently, or not partitioned. Partitioning is not carried over to the new table. Specify any desired partitioning as part of the CREATE TABLE statement before the AS subquery clause.

On the new table, you can choose whether to partition like the old table , Or different partition forms , Or create a non partitioned table . stay AS subquery Specify before the sentence .

> A column that is encrypted using Transparent Data Encryption in the selected table will not be encrypted in the new table unless you define the column in the new table as encrypted at create time.

TDE The column of will not be brought to the new table .

therefore , Common attributes like constraints , There will be these hidden phenomena , The technical field of database is really abstruse , And this may be the charm of Technology , Problems encountered 、 Explore the problem 、 solve the problem , Always enjoy it .

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