Which two statements are true about constraints? （）A、The UNIQUE constraint does not permit a null value for the column.B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.D、The NOT NULL constraint ensures that null values are not permitted for the column.
Which two statements are true about constraints? （）
- A、The UNIQUE constraint does not permit a null value for the column.
- B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.
- C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.
- D、The NOT NULL constraint ensures that null values are not permitted for the column.
相关考题：
The InnoDB engine has a feature known as clustered indexes.Which three statements are true about clustered indexes as used in InnoDB?() A.A primary key must exist for creation of a clustered indexB.A clustered index allows fulltext searching within InnoDBC.The first unique index is always used as a clustered index and not a primary keyD.A clustered index provides direct access to a page containing row dataE.If no indexes exist, a hidden clustered index is generated based on row IDsF.A primary key is used as a clustered indexG.A clustered index is a grouping of indexes from different tables into a global index for faster searching
Which of the following scenarios will ensure that the value of the NEXT_STEPNO column in a given row of table TABLEX exists as a value of column STEPNO (usually in another row) in the same table?() A.Define a UNIQUE constraint on the columns NEXT_STEPNO and STEPNO.B.Define a CHECK constraint on the NEXT_STEPNO column (NEXT_STEPNO = STEPNO).C.Define column STEPNO as the primary key of TABLEX and column NEXT_STEPNO as a foreign key referencing column STEPNO of the same table.D.Define column NEXT_STEPNO as the primary key of TABLEX and column STEPNO as a foreign key referencing column NEXT_STEPNO in the same table.
Given the following requirements:Create a table to contain employee data, with a unique numeric identifier automatically assigned when a row is added, has an EDLEVEL column that permits only the values ‘C‘, ‘H‘ and ‘N‘, and permits inserts only when a corresponding value for the employee‘s department exists in the DEPARTMENT table.Which of the following CREATE statements will successfully create this table?（）A.CREATE TABLE emp ( empno SMALLINT NEXTVAL GENERATED ALWAYS AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1), PRIMARY KEY emp_pk (empno), FOREIGN KEY emp_workdept_fk ON (workdept) REFERENCES department (deptno), CHECK edlevel_ck VALUES (edlevel IN (‘C‘,‘H‘,‘N‘)), );B.CREATE TABLE emp ( empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK edlevel VALUES (‘C‘,‘H‘,‘N‘) );C.CREATE TABLE emp ( empno SMALLINT NEXTVAL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1) CHECK IN (‘C‘,‘H‘,‘N‘)), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY department (deptno) REFERENCES (workdept) );D.CREATE TABLE emp ( empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK (edlevel IN (‘C‘,‘H‘,‘N‘)) );
Which of the following scenarios will ensure that the value of the NEXT_STEPNO column in a given row of table TABLEX exists as a value of column STEPNO (usually in another row) in the same table?（）A、Define a UNIQUE constraint on the columns NEXT_STEPNO and STEPNO.B、Define a CHECK constraint on the NEXT_STEPNO column (NEXT_STEPNO = STEPNO).C、Define column STEPNO as the primary key of TABLEX and column NEXT_STEPNO as a foreign key referencing column STEPNO of the same table.D、Define column NEXT_STEPNO as the primary key of TABLEX and column STEPNO as a foreign key referencing column NEXT_STEPNO in the same table.
在设计数据库时，要充分考虑数据的完整性或准确性。下面关于primary key和unique的描述错误的是（）A、设为unique的列的值是不能重复的，用来唯一区别unique列的值B、primary key列不可以有null值，而unique列是可以有null的C、primary key列和unique列都不可以有null值D、primary key用来在表中设置主键，主键列的值是可以重复的，用来唯一标识表中的每一条记录
Given the following requirements: Create a table to contain employee data, with a unique numeric identifier automatically assigned when a row is added, has an EDLEVEL column that permits only the values 'C', 'H' and 'N', and permits inserts only when a corresponding value for the employee's department exists in the DEPARTMENT table. Which of the following CREATE statements will successfully create this table?（）A、CREATE TABLE emp ( empno SMALLINT NEXTVAL GENERATED ALWAYS AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1), PRIMARY KEY emp_pk (empno), FOREIGN KEY emp_workdept_fk ON (workdept) REFERENCES department (deptno), CHECK edlevel_ck VALUES (edlevel IN ('C','H','N')), );B、CREATE TABLE emp ( empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK edlevel VALUES ('C','H','N') );C、CREATE TABLE emp ( empno SMALLINT NEXTVAL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1) CHECK IN ('C','H','N')), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY department (deptno) REFERENCES (workdept) );D、CREATE TABLE emp ( empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK (edlevel IN ('C','H','N')) );
When defining a referential constraint between the parent table T2 and the dependent table T1, which of the following is true?（）A、The list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.B、The list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.C、The list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.D、The list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.
Evaluate the CREATE TABLE statement： CREATE TABLE products （product_id NUMBER （6） CONSTRAINT prod_id_pk PRIMARY KEY， product_name VARCHAR2 （15））； Which statement is true regarding the PROD_ID_PK constraint？（）A、 It would be created only if a unique index is manually created first.B、 It would be created and would use an automatically created unique index.C、 It would be created and would use an automatically created nonunique index.D、 It would be created and remains in a disabled state because no index is specified in the command.
For which two constraints does the Oracle Server implicitly create a unique index?（）A、NOT NULLB、PRIMARY KEYC、FOREIGN KEYD、CHECKE、UNIQUE
Which two statements are true about the primary key constraint in a table？ （）A、It is not possible to disable the primary key constraint.B、It is possible to have more than one primary key constraint in a single table.C、The primary key constraint can be referred by only one foreign key constraint.D、The primary key constraint can be imposed by combining more than one column.E、The non-deferrable primary key constraint creates an unique index on the primary key column if it is not already indexed.
Which two statements are true about a bitmap index？ （）A、It is recommended for the columns that have unique values.B、It can be converted to a B-tree index by using the ALTER INDEX command.C、It has a bitmap segment for each distinct value in the key column， containing a string of bits in which each bit represents the presence or absence of a key column value.D、Updating the key column locks the whole bitmap segment that contains the bit for the key value to be updated.
Examine the command that is used to create a table： SQL CREATE TABLE orders（oid NUMBER（6） PRIMARY KEY， odate DATE， ccode NUMBER（6）， oamt NUMBER（10，2）） TABLESPACE users； Which two statements are true about the effect of the above command） （）A、A CHECK constraint is created on the OID column.B、A NOT NULL constraint is created on the OID column.C、The ORDERS table is the only object created in the USERS tablespace.D、The ORDERS table and a unique index are created in the USERS tablespace.E、The ORDERS table is created in the USERS tablespace and a unique index is created on the OIDcolumn in the SYSTEM tablespace.
Which statement is true about loading data using the conventional path of SQL*Loader（）A、Redo is not generated while performing conventional path loads.B、Only PRIMARY KEY， UNIQUE KEY， and NOT NULL constraints are checked.C、No exclusive locks are acquired when the conventional path loads are performed.D、Instead of performing transactions， SQL*Loader directly writes data blocks to the data files.E、INSERT triggers are disabled before the conventional path load and reenabled at the end of the load.
Which statements are correct regarding indexes？ （）A、 When a table is dropped， the corresponding indexes are automatically dropped.B、 For each DML operation performed， the corresponding indexes are automatically updated.C、 Indexes should be created on columns that are frequently referenced as part of an expression.D、 A non-deferrable PRIMARY KEY or UNIQUE KEY constraint in a table automatically creates a uniqueindex.
Which statement is true about loading data using the conventional path of SQL*Loader（）A、Redo is not generated while performing conventional path loads.B、Only PRIMARY KEY， UNIQUE KEY， and NOT NULL constraints are checked.C、No exclusive locks are acquired when the conventional path loads are performed.D、Instead of performing transactions， SQL*Loader directly writes data blocks to the data files.E、INSERT triggers are disabled before the conventional path load and reenabled at the end of the load
The InnoDB engine has a feature known as clustered indexes. Which three statements are true about clustered indexes as used in InnoDB?（）A、A primary key must exist for creation of a clustered indexB、A clustered index allows fulltext searching within InnoDBC、The first unique index is always used as a clustered index and not a primary keyD、A clustered index provides direct access to a page containing row dataE、If no indexes exist, a hidden clustered index is generated based on row IDsF、A primary key is used as a clustered indexG、A clustered index is a grouping of indexes from different tables into a global index for faster searching
多选题Examine the command that is used to create a table： SQL CREATE TABLE orders（oid NUMBER（6） PRIMARY KEY， odate DATE， ccode NUMBER （6）， oamtNUMBER（10，2）） TABLESPACE users； Which two statements are true about the effect of the above command（）AA CHECK constraint is created on the OID column.BA NOT NULL constraint is created on the OID column.CThe ORDERS table is the only object created in the USERS tablespace.DThe ORDERS table and a unique index are created in the USERS tablespace.EThe ORDERS table is created in the USERS tablespace and a unique index is created on the OID columnin the SYSTEM tablespace.
多选题The InnoDB engine has a feature known as clustered indexes. Which three statements are true about clustered indexes as used in InnoDB?（）AA primary key must exist for creation of a clustered indexBA clustered index allows fulltext searching within InnoDBCThe first unique index is always used as a clustered index and not a primary keyDA clustered index provides direct access to a page containing row dataEIf no indexes exist, a hidden clustered index is generated based on row IDsFA primary key is used as a clustered indexGA clustered index is a grouping of indexes from different tables into a global index for faster searching
单选题Evaluate the CREATE TABLE statement： CREATE TABLE products （product_id NUMBER （6） CONSTRAINT prod_id_pk PRIMARY KEY， product_name VARCHAR2 （15））； Which statement is true regarding the PROD_ID_PK constraint？（）A It would be created only if a unique index is manually created first.B It would be created and would use an automatically created unique index.C It would be created and would use an automatically created nonunique index.D It would be created and remains in a disabled state because no index is specified in the command.
单选题View the Exhibit and examine the structure of the EMP table. You executed the following command to add a primary key to the EMP table： ALTER TABLE emp ADD CONSTRAINT emp_id_pk PRIMARY KEY （emp_id） USING INDEX emp_id_idx； Which statement is true regarding the effect of the command？（）A The PRIMARY KEY is created along with a new index.B The PRIMARY KEY is created and it would use an existing unique index.C The PRIMARY KEY would be created in a disabled state because it is using an existing index.D The statement produces an error because the USING clause is permitted only in the CREATE TABLE command.
多选题Which two statements are true about a bitmap index？ （）AIt is recommended for the columns that have unique values.BIt can be converted to a B-tree index by using the ALTER INDEX command.CIt has a bitmap segment for each distinct value in the key column， containing a string of bits in which each bit represents the presence or absence of a key column value.DUpdating the key column locks the whole bitmap segment that contains the bit for the key value to be updated.
多选题Which two statements are true about constraints? （）AThe UNIQUE constraint does not permit a null value for the column.BA UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.CThe PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.DThe NOT NULL constraint ensures that null values are not permitted for the column.
单选题Given the following requirements: Create a table to contain employee data, with a unique numeric identifier automatically assigned when a row is added, has an EDLEVEL column that permits only the values 'C', 'H' and 'N', and permits inserts only when a corresponding value for the employee's department exists in the DEPARTMENT table. Which of the following CREATE statements will successfully create this table?（）ACREATE TABLE emp ( empno SMALLINT NEXTVAL GENERATED ALWAYS AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1), PRIMARY KEY emp_pk (empno), FOREIGN KEY emp_workdept_fk ON (workdept) REFERENCES department (deptno), CHECK edlevel_ck VALUES (edlevel IN ('C','H','N')), );BCREATE TABLE emp ( empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK edlevel VALUES ('C','H','N') );CCREATE TABLE emp ( empno SMALLINT NEXTVAL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1) CHECK IN ('C','H','N')), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY department (deptno) REFERENCES (workdept) );DCREATE TABLE emp ( empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK (edlevel IN ('C','H','N')) );
多选题Which two statements are true about the primary key constraint in a table？ （）AIt is not possible to disable the primary key constraint.BIt is possible to have more than one primary key constraint in a single table.CThe primary key constraint can be referred by only one foreign key constraint.DThe primary key constraint can be imposed by combining more than one column.EThe non-deferrable primary key constraint creates an unique index on the primary key column if it is not already indexed.
多选题Which statements are correct regarding indexes？ （）AWhen a table is dropped， the corresponding indexes are automatically dropped.BFor each DML operation performed， the corresponding indexes are automatically updated.CIndexes should be created on columns that are frequently referenced as part of an expression.DA non-deferrable PRIMARY KEY or UNIQUE KEY constraint in a table automatically creates a uniqueindex.
多选题For which two constraints does the Oracle Server implicitly create a unique index? （）ANOT NULLBPRIMARY KEYCFOREIGN KEYDCHECKEUNIQUE
单选题When defining a referential constraint between the parent table T2 and the dependent table T1, which of the following is true?（）AThe list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.BThe list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.CThe list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.DThe list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.