Question

我想限制实体中的行数。例如，我创建了一个表系列（id，name），我希望在族表中不能插入超过5行。任何有此建议的人都将不胜感激。

Answer 1

对于聚合或来自多个表的数据的约束，可以创建帮助器MATERIALIZED VIEW：

HUSQVIK@HQ_PDB_TCP> CREATE TABLE family (id NUMBER PRIMARY KEY, name VARCHAR2(255));

Table created.

HUSQVIK@HQ_PDB_TCP> CREATE MATERIALIZED VIEW LOG ON family WITH ROWID INCLUDING NEW VALUES;

Materialized view log created.

CREATE MATERIALIZED VIEW family_count
REFRESH FAST ON COMMIT
AS SELECT count(*) family_count FROM family;

Materialized view created.

HUSQVIK@HQ_PDB_TCP> ALTER MATERIALIZED VIEW family_count ADD CONSTRAINT max_family_count CHECK (family_count <= 5);

Materialized view altered.

HUSQVIK@HQ_PDB_TCP> INSERT INTO family (id, name) values (1, 'Family 1');

1 row created.

HUSQVIK@HQ_PDB_TCP> INSERT INTO family (id, name) values (2, 'Family 2');

1 row created.

HUSQVIK@HQ_PDB_TCP> INSERT INTO family (id, name) values (3, 'Family 3');

1 row created.

HUSQVIK@HQ_PDB_TCP> INSERT INTO family (id, name) values (4, 'Family 4');

1 row created.

HUSQVIK@HQ_PDB_TCP> INSERT INTO family (id, name) values (5, 'Family 5');

1 row created.

HUSQVIK@HQ_PDB_TCP> COMMIT;

Commit complete.

HUSQVIK@HQ_PDB_TCP> INSERT INTO family (id, name) values (6, 'Family 6');

1 row created.

HUSQVIK@HQ_PDB_TCP> COMMIT;
COMMIT
*
ERROR at line 1:
ORA-12008: error in materialized view refresh path
ORA-02290: check constraint (HUSQVIK.MAX_FAMILY_COUNT) violated

甲骨文限制实体中的行数

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