DataBase Administrator (DBA) Interview Questions and Answers
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106. Explain UNION, MINUS, UNION ALL and INTERSECT?
The UNION command is used to select related information from two tables, much like the JOIN command. However, when using the UNION command all selected columns need to be of the same data type.The UNION ALL command is equal to the UNION command, except that UNION ALL selects all values.INTERSECT - Return only those rows that are in *both* SELECT statements.MINUS - Return the rows that are in the first SELECT but not the second.
107. What are the types of SQL statement?
4 TYPES OF SQL STATEMENTS ARE THERE
108. What is a pseudo column. Give some examples?
pseudo columns are used to access object content and other information
109. What is difference between CHAR and VARCHAR2?
The difference between a CHAR and a VARCHAR is that a CHAR(n) will ALWAYS be N bytes long, it will be blank padded upon insert to ensure this. A varchar2(n) on the other hand will be 1 to N bytes long, it will NOT be blank padded
110. What do you know about subqueries?
A subquery is a query within a query. In Oracle, you can create subqueries within your SQL statements. These subqueries can reside in the WHERE clause, the FROM clause, or the SELECT clause.
111. What is a database link?
It is a named object that describes a ‘path’ from one database to another.
112. How to drop the index ?
drop index index-name;.
113. What are the different types of SQL statements?
SQL statements are divided into five categories:
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