SQL INTERVIEW QUESTION & ANSWERS
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| 46. | What is multiple column subquery? |
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| A multiple column subquery returns more than one column. In a multiple column subquery, the resulting rows of the subquery are evaluated pair wise (that is column to column and row to row comparisons) in the main query. |
| 47. | What is correlated subqueries? |
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| A correlated subquery is the SELECT statement that is nested inside another query containing the reference of one or more columns in the outer query. |
| 48. | What is the difference between nextval and currval? |
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| The NEXTVAL pseudocolumn increments the current value of a sequence and returns the next value of the sequence. The CURRVAL pseudocolumn returns the current value of a sequence. |
| 49. | What is deadlocks? |
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| A deadlock occurs when two transactions hold locks and each is waiting for a lock held by the other session. In the sample sessions below, two users hold clashing locks. Oracle detects this deadlock condition (usually within a couple of seconds) and raises an exception in one of the sessions. |
| Posted by Dinesh Sati. (Oct 05, 2013) | |
When two process are waiting for same object (updating same row) which is held by any other process is called deadlock condition. |
| 50. | What is the difference between Apache and Oracle HTTP server? |
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| Oracle HTTP server is the customized form of the Apache. Oracle has customized the Apache Web server as per its own requirement which is known as the Oracle HTTP server. |