You can’t have LOB data types (CLOB, BLOB, BFILE) ordered. Oracle will trigger an error when you try to order on LOB fields Same with grouping. You can’t apply GROUP BY on LOB fields. It will raise the same error.
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When you modify existing column with DEFAULT value, then modification to add a DEFAULT value takes effect only from subsequent insertions to the table. Let’s have a look at EMP table below. All DEFAULT values are set to NULL at this point Let’s modify EMP .COMMISION_PCT DEFAULT value to 0.777 Now, the EMP .COMMISION_PCT […]
To suppress duplicates in a SELECT statement both clauses DISTINCT and UNIQUE can be used, though only DISTINCT is mentioned more widely than UNIQUE. Both clauses are valid and work. ( see below ) DISTINCT UNIQUE
It is normal if some or all grouping attributes will not be present in SELECT statement. The grouping will work anyway. SELECT statement is for presentation, while actual grouping is done by GROUP BY. An example below demonstrated a typical case for usage SELECT attributes and GROUP BY attributes. Both […]
Pay attention, TO_NUMBER needs a dot, not a comma On the exam, you will be limited in time and may not pay attention to details. And may lose some points therefore on simple questions like that. You will have a good portion of questions which requires attention rather than knowledge or […]
An inline view is a SELECT statement in the FROM-clause of another SELECT statement. In the query below the INLINE VIEW is : (SELECT AVG(salary) avg_salary from employees ) Inline views are commonly used to simplify complex queries by removing join operations and condensing several separate queries into a single query. So, the purpose of INLINE VIEW is to […]
A non-equijoin is represented by the use of an operator other than equality operator. A non-equijoin is used when no corresponding columns exist between the tables in the query, but rather a relationship exists between two columns having compatible data types. Several conditions can be used to define a non-equijoin, […]
This is a tricky behavior of SUM() function which is going to be tested for sure on the exam; We perceive the main purpose of SUM() function as a summation of all elements it may be applied on. But two almost identical SUM() function usages will give you the different results, […]
This is a typical situation that can confuse an average student on the exam. We all know that using a subquery that returns multiple rows if forbidden with parent query if parent query refer subquery with any of those =, >, >=, <, <=, <>, != If we use =, […]