Which of the following is a Data Definition Language (DDL) command in SQL?
- A.INSERT
- B.CREATE
- C.SELECT
- D.UPDATE
Correct answer
Explanation
The correct answer is B, CREATE. The Data Definition Language deals with the structure of the database rather than with the data inside it, and CREATE is its basic command, used to build a table, a view or the database itself; ALTER, DROP, TRUNCATE and RENAME belong to the same group. Option A is wrong because INSERT adds new rows to an existing table and is therefore a Data Manipulation Language command. Option C is wrong because SELECT reads rows and returns a result set, which is again manipulation of data, not definition of structure; some books place it in a separate Data Query Language. Option D is wrong because UPDATE changes values already stored in rows and is also DML. Remember the split by what changes: structure means DDL, contents mean DML, rights mean DCL with GRANT and REVOKE.
Read the full article: Databases and DBMS: Models, Keys, SQL and Normalisation
Practice Questions
View allWhich of the following is the oldest database model?
- A.Hierarchical
- B.Object oriented
- C.Deductive
- D.Relational
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The hierarchical model is the first data model used in commercial database software; IBM built its Information Management System on it in the 1960s for the Apollo programme.
Read the full explanation →Who proposed the relational model of databases?
- A.Charles Babbage
- B.Edgar Frank Codd
- C.Dennis Ritchie
- D.James Gosling
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Codd, a British computer scientist working at IBM, set out the relational model in a paper published in 1970, proposing that all data be held in simple two-dimensional tables and joined by matching values rather than by fixed pointers.
Read the full explanation →In relational database terminology, a row of a table is called a:
- A.Attribute
- B.Domain
- C.Tuple
- D.Relation
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In the vocabulary of the relational model a table is a relation, and one complete horizontal entry of that table, such as all the details of a single student, is a tuple; the ordinary words for it are row and record.
Read the full explanation →Which SQL command removes all the rows of a table but keeps the table structure, and is classified as a DDL command?
- A.DELETE
- B.DROP
- C.TRUNCATE
- D.ERASE
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TRUNCATE empties a table in one operation, leaving the columns, data types and constraints in place so that the table can be filled again at once; because it changes the object rather than selected rows it is grouped with the Data Definition Language and it is much faster than deleting…
Read the full explanation →Which key uniquely identifies each record in a table and can never contain a null value?
- A.Foreign key
- B.Alternate key
- C.Primary key
- D.Super key
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The designer picks one candidate key as the primary key of a table, and the database then enforces two rules on it: its value must be different in every row, and it can never be left null, since a missing value would make a row impossible to identify.
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