What is difference between Varray and nested table in Oracle?
Differences Between Varrays And Nested Tables
A Varray which is stored in a database maintains its subscripts and sequence. It is always maintained as a single object. Whereas, the nested tables are used when the count of the number of elements is not restricted.
What is nested table in Oracle with example?
Within the database, nested tables can be considered one-column database tables. Oracle stores the rows of a nested table in no particular order. But, when you retrieve the nested table into a PL/SQL variable, the rows are given consecutive subscripts starting at 1. That gives you array-like access to individual rows.
Can we use ORDER BY and group by Together in Oracle?
The Oracle documentation says that an expression can be used but the expression must be based on the columns in the selection list.
Does the order of columns in WHERE clause matter in Oracle?
No, that order doesn’t matter (or at least: shouldn’t matter). Any decent query optimizer will look at all the parts of the WHERE clause and figure out the most efficient way to satisfy that query.
What is the difference between index by table and nested tables?
Nested table collections are an extension of the index-by tables. The main difference between the two is that nested tables can be stored in a database column but index-by tables cannot.
Why should we use Dbms_utility Format_error_backtrace?
Description The DBMS_UTILITY. format_error_backtrace function, added in Oracle Database 10g Release 2, is a critical subprogram to call when logging exceptions. It returns a string that traces the error back to the line on which it was raised!
What is the use of nested table?
A nested table is represented in the case table as a special column that has a data type of TABLE. For any particular case row, this kind of column contains selected rows from the child table that pertain to the parent table. The data in a nested table can be used for prediction or for input, or for both.
Can you use ORDER BY and GROUP BY in same query?
Both GROUP BY and ORDER BY are clauses (or statements) that serve similar functions; that is to sort query results. However, each of these serve very different purposes; so different in fact, that they can be employed separately or together.
How do you use GROUP BY and ORDER BY together?
only selects rows from table that match a row from the subquery (this operation — where a join is performed, but no columns are selected from the second table, it’s just used as a filter — is known as a “semijoin” in case you were curious) orders the rows.
Does the order of the WHERE clause make a difference?
In theory, there is no difference. Occasionally, especially with the simpler optimizers, there are differences in the query plan depending on the order of the clauses in the WHERE clause. There’s a moderately strong argument that such differences are symptomatic of a bug. Similar comments apply to join order, too.
Does the order of table matter?
Generally, no, the order of the tables in the JOIN will not affect the overall results of the query. As long as you specify what columns to select, the results should appear essentially the same, just that the rows will be ordered according to the appearance in the first table.
What is difference between collections and records in Oracle?
To create a collection variable, you either define a collection type and then create a variable of that type or use %TYPE . In a record, the internal components can have different data types, and are called fields.
Can we delete element from Varray in Oracle?
You cannot delete individual elements from a VARRAY collection type.
What is Dbms_utility Format_error_stack?
Originally FORMAT_ERROR_STACK was meant to replace SQLERRM, because the latter would mutilate error messages longer than 512 characters. DBMS_UTILITY. FORMAT_ERROR_BACKTRACE on the other hand contained and still contains the calling path that lead to an exception.
What is Dbms_utility Format_call_stack?
DBMS_UTILITY.FORMAT_CALL_STACK. Description Use the DBMS_UTILITY. FORMAT_CALL_STACK function to answer the question “How did I get here?”. Note that this function only shows you the name of the program unit (e.g., package name) and not the name of the subprogram in that program unit.
What is meant by nested table?
nesting table in American English. noun. one of a set of usually three or four small tables that are graduated in size so that they may be stacked on top of one another. Also called: stack table.
Which comes first ORDER BY or GROUP BY?
Group By in SQL:
It is used to arrange similar data into the group. The GROUP BY clause follows the WHERE clause and comes before the ORDER BY clause.
Which is better ORDER BY or GROUP BY?
Key Differences between GROUP BY and ORDER BY
The Group By clause is used to group data based on the same value in a specific column. The ORDER BY clause, on the other hand, sorts the result and shows it in ascending or descending order. It is mandatory to use the aggregate function to use the Group By.
Can we use ORDER BY and GROUP BY in same query SOQL?
Field that are aggregated cannot be used in GROUP BY or ORDER BY.
Which comes first ORDER BY or WHERE?
The ORDER BY clause must come after the WHERE, GROUP BY, and HAVING clause if present in the query. Use ASC or DESC to specify the sorting order after the column name.
Does ORDER BY go before WHERE?
ORDER BY is always put at the very end of the query.
Clauses like FROM , WHERE , GROUP BY , HAVING , etc. should be put before the ORDER BY keyword. To sort the output in ascending order, you may put the keyword ASC after the column name. However, that’s optional, since it will sort in ascending by default.
What order should tables be joined?
The join order is the order in which the tables are joined together in a multi-table SQL statement. Ideally, a plan should start with the join that eliminates the most data to minimize the amount of data carried into the subsequent joins.
Does the order of tables matter in inner join?
The order doesn’t matter for INNER joins. As long as you change your selects from SELECT * to SELECT a.
What is Pragma Autonomous_transaction?
The AUTONOMOUS_TRANSACTION pragma changes the way a subprogram works within a transaction. A subprogram marked with this pragma can do SQL operations and commit or roll back those operations, without committing or rolling back the data in the main transaction.
How many types of tables are there in Oracle?
The most common type of table in an Oracle database is a relational table, which is structured with simple columns similar to the employees table. Two other table types are supported: object tables and XMLType tables. Any of the three table types can be defined as permanent or temporary.