Oracle 12c automatically creates an index for which type of constraints?a. NOT NULLb. PRIMARY KEYc. FOREIGN KEYd. UNIQUE KEYe. none of the abovef. only a and bg. only b and d
SQL
SQL stands for Structured Query Language, is a form of communication that uses queries structured in a specific format to store, manage & retrieve data from a relational database.
Queries
A query is a type of computer programming language that is used to retrieve data from a database. Databases are useful in a variety of ways. They enable the retrieval of records or parts of records, as well as the performance of various calculations prior to displaying the results. A search query is one type of query that many people perform several times per day. A search query is executed every time you use a search engine to find something. When you press the Enter key, the keywords are sent to the search engine, where they are processed by an algorithm that retrieves related results from the search index. Your query's results are displayed on a search engine results page, or SER.
Oracle 12c automatically creates an index for which type of constraints?
a. NOT NULL
b. PRIMARY KEY
c. FOREIGN KEY
d. UNIQUE KEY
e. none of the above
f. only a and b
g. only b and d
Primary key:
- Primary key constraint gives uniqueness to an index.
- It uniquely defines a record and it has a single field or combination of fields.
- For primary key constraints Oracle 12c creates an index automatically.
Unique key:
- It has same properties like primary key.
- These two keys are created for a column. By using unique key and primary key the user need not to perform full table scan, a value in a table can find without full table scan.
- Unique key creates an index in Oracle 12c automatically.
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