Quick Answer: Which Statement Is Wrong About Primary Key Constraint In SQL?

What does constraint mean?


The definition of a constraint is something that imposes a limit or restriction or that prevents something from occurring.

An example of a constraint is the fact that there are only so many hours in a day to accomplish things.

YourDictionary definition and usage example..

Which statement is wrong about primary key constraint in SQL *?

Q. 1. Which statement is wrong about PRIMARY KEY constraint in SQL? Primary keys must contain UNIQUE values.

What is the meaning of like ‘% 0 0 %’?

What is the meaning of LIKE ‘%0%0%’ A. Feature begins with two 0’s. Feature ends with two 0’s. Feature has more than two 0’s.

Can a table have no primary key?

Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.

What does like mean?

(Entry 1 of 9) transitive verb. 1a : to feel attraction toward or take pleasure in : enjoy likes baseball. b : to feel toward : regard how would you like a change.

What operator tests column for the absence of data?

Answer: The operator that tests column for the absence of data is an option “B) is NULL operator”. The reason for this answer is because the NULL operator is used in the database for representing that a particular field is empty.

Can a foreign key be null?

A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts. … A table can have many foreign keys.

Which statement is true for a primary key constraint?

The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).

Which of the following is a constraint?

How many types of constraints are present in SQL Server? Explanation: Constraints are Primary key, Foreign Key, Unique Key, Not Null, Check, Default.

Which SQL keyword is used to retrieve a maximum value?

Which SQL keyword is used to retrieve a maximum value? Explanation: The MAX() function returns the largest value of the selected column.

Which SQL keyword is used to retrieve only unique values?

DISTINCT keywordThe distinct keyword is used with SELECT statement to retrieve unique values from the table.

Which is not a DDL command?

In SQL, which of the following is not a data definition language commands? Explanation: With RENAME statement you can rename a table. RENAME, REVOKE and GRANT are DDL commands and UPDATE is DML command.

Which SQL statement is used to update data in a database?

The UPDATE statement updates data values in a database. UPDATE can update one or more records in a table. Use the WHERE clause to UPDATE only specific records.

Can primary key be changed?

A table’s primary key should be explicitly defined in the CREATE TABLE statement. … 1: You can change the primary key of an existing table with an ALTER TABLE … ALTER PRIMARY KEY statement, or by using DROP CONSTRAINT and then ADD CONSTRAINT in the same transaction. For more information, see Details.

Can a primary key be a foreign key?

Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.

Which is correct statement about primary key of a table?

A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values. A table can have only one primary key, which may consist of single or multiple fields.

What is a primary key with example?

A primary key is either an existing table column or a column that is specifically generated by the database according to a defined sequence. For example, students are routinely assigned unique identification (ID) numbers, and all adults receive government-assigned and uniquely-identifiable Social Security numbers.

What is the use of primary key?

A primary key is used to ensure data in the specific column is unique. You can only set constraints with primary keys, by setting a foreign key to another column which creates a relationship with the column that has the primary key set. A prime use of a primary key is in the case of a users table.

Which sorts rows in SQL?

The SQL ORDER BY Keyword The ORDER BY keyword is used to sort the result-set in ascending or descending order. The ORDER BY keyword sorts the records in ascending order by default. To sort the records in descending order, use the DESC keyword.

What is a constraint in DBMS?

Constraints are the rules enforced on the data columns of a table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database. … PRIMARY Key − Uniquely identifies each row/record in a database table.

How do I write a constraint in SQL?

The following constraints are commonly used in SQL:NOT NULL – Ensures that a column cannot have a NULL value.UNIQUE – Ensures that all values in a column are different.PRIMARY KEY – A combination of a NOT NULL and UNIQUE. … FOREIGN KEY – Uniquely identifies a row/record in another table.More items…