More flexible. Data is stored in separate table. Stored outside the table DML are allowed. VArrays Bounded Individual element cannot be deleted. Stored by Oracle in- line Do not support indexes. Not flexible than nested table. Data is stored as single object in database.
Stored within table. DML are not allowed. Please Turn OFF your ad blocker. Learn More. What is nested table in Oracle and difference between table and nested table? First Prev Next Last. Showing Answers 1 - 7 of 7 Answers. A nested table can be stored as a database column. I cannot think of a good reason to constrain my array size artificially when I don't have to.
In PLSQL code, there is very little difference between a varray and nested table type the fixed order issue isn't an issue with PLSQL nested tables, they are just like varrays -- its only when you SAVE the nested table to a database table that the order might be different when you read it back in In SQL using these in create tables -- well, there I don't really have any advice.
I've used a varray everynow and then but stick to relation constructs pretty much. If I've a need of a nested table construct, I set up a parent child relationship. I cannot compare a record to a table -- they are orthogonal to eachother.
You can have a table of records A record is used to hold a row, you can use a table of records to hold many rows at the same time. They are somewhat apples and oranges. The static cursor will be parsed ONCE per session typically unless it gets flushed out o the ref cursor can point to a different query time it is opened hence the need to parse each time, its not static.
Updating Rows with Records. Restrictions on Record Inserts and Updates. The components of an explicitly listed composite data structure such as a collection constructor or record initializer can be evaluated in any order. If a program determines order of evaluation, then at the point where the program does so, its behavior is undefined.
Table summarizes their similarities and differences. If the number of elements is specified, it is the maximum number of elements in the collection. If the number of elements is unspecified, the maximum number of elements in the collection is the upper limit of the index type. A sparse collection has gaps between elements. An empty collection exists but has no elements. A null collection also called an atomically null collection does not exist.
To change a null collection to an existing collection, you must initialize it, either by making it empty or by assigning a non- NULL value to it for details, see " Collection Constructors " and " Assigning Values to Collection Variables ". It is available only in the block, and is stored in the database only if the block is in a standalone or package subprogram.
Standalone and package subprograms are explained in " Nested, Package, and Standalone Subprograms ". A collection type defined in a package specification is a public item. It is stored in the database until you drop the package. A collection type defined at schema level is a standalone type. A collection type defined in a package specification is incompatible with an identically defined local or standalone collection type see Example and Example To be an ADT attribute data type, a collection type must be a standalone collection type.
For other restrictions, see Restrictions on datatype. For example:. Indexes are stored in sort order, not creation order. Declaring Associative Array Constants. Appropriate Uses for Associative Arrays. Table for a summary of associative array characteristics. This example defines a type of associative array indexed by string, declares a variable of that type, populates the variable with three elements, changes the value of one element, and prints the values in sort order, not creation order.
When declaring an associative array constant, you must create a function that populates the associative array with its initial value and then invoke the function in the constant declaration. For information about constructors, see " Collection Constructors ". In this example, the function does for the associative array what a constructor does for a varray or nested table. Passing Associative Arrays to Remote Databases. Oracle Database Globalization Support Guide for information about linguistic sort parameters.
If you must change these parameter values during your session, restore their original values before operating on associative arrays indexed by string. If your indexes have data types other than VARCHAR2 and its subtypes, ensure that these indexes remain consistent and unique if the values of initialization parameters change. A relatively small lookup table, which can be constructed in memory each time you invoke the subprogram or initialize the package that declares it.
Declare formal subprogram parameters of associative array types. You cannot declare an associative array type at schema level. Therefore, to pass an associative array variable as a parameter to a standalone subprogram, you must declare the type of that variable in a package specification.
Doing so makes the type available to both the invoked subprogram which declares a formal parameter of that type and the invoking subprogram or anonymous block which declares and passes the variable of that type. See Example An associative array is intended for temporary data storage.
To make an associative array persistent for the life of a database session, declare it in a package specification and populate it in the package body.
A varray variable-size array is an array whose number of elements can vary from zero empty to the declared maximum size. The lower bound of index is 1; the upper bound is the current number of elements.
The upper bound changes as you add or delete elements, but it cannot exceed the maximum size. When you store and retrieve a varray from the database, its indexes and element order remain stable. Figure shows a varray variable named Grades , which has maximum size 10 and contains seven elements.
Grades n references the n th element of Grades. The upper bound of Grades is 7, and it cannot exceed The database stores a varray variable as a single object. If a varray variable is less than 4 KB, it resides inside the table of which it is a column; otherwise, it resides outside the table but in the same tablespace. An uninitialized varray variable is a null collection. You must initialize it, either by making it empty or by assigning a non- NULL value to it.
Appropriate Uses for Varrays. Table for a summary of varray characteristics. This example defines a local VARRAY type, declares a variable of that type initializing it with a constructor , and defines a procedure that prints the varray. The example invokes the procedure three times: After initializing the variable, after changing the values of two elements individually, and after using a constructor to the change the values of all elements.
For an example of a procedure that prints a varray that might be null or empty, see Example Because you must store or retrieve all elements at the same time, a varray might be impractical for large numbers of elements.
In the database, a nested table is a column type that stores an unspecified number of rows in no particular order. Using these indexes, you can access the individual rows of the nested table variable. The indexes and row order of a nested table might not remain stable as you store and retrieve the nested table from the database. The amount of memory that a nested table variable occupies can increase or decrease dynamically, as you add or delete elements. An uninitialized nested table variable is a null collection.
Appropriate Uses for Nested Tables. Table for a summary of nested table characteristics. This example defines a local nested table type, declares a variable of that type initializing it with a constructor , and defines a procedure that prints the nested table.
The example invokes the procedure three times: After initializing the variable, after changing the value of one element, and after using a constructor to the change the values of all elements. After the second constructor invocation, the nested table has only two elements.
Referencing element 3 would raise error ORA Conceptually, a nested table is like a one-dimensional array with an arbitrary number of elements. However, a nested table differs from an array in these important ways:. An array has a declared number of elements, but a nested table does not. The size of a nested table can increase dynamically.
An array is always dense. A nested array is dense initially, but it can become sparse, because you can delete elements from it. Figure shows the important differences between a nested table and an array. Nested table data is stored in a separate store table, a system-generated database table. When you access a nested table, the database joins the nested table with its store table. This makes nested tables suitable for queries and updates that affect only some elements of the collection.
You would create a separate lookup table, with multiple entries for each row of the main table, and access it through join queries. A collection constructor constructor is a system-defined function with the same name as a collection type, which returns a collection of that type. This topic applies only to varrays and nested tables. Associative arrays do not have constructors.
In this topic, collection means varray or nested table. If the parameter list is empty, the constructor returns an empty collection. Otherwise, the constructor returns a collection that contains the specified values. You can assign the returned collection to a collection variable of the same type in the variable declaration and in the executable part of a block.
This example invokes a constructor twice: to initialize the varray variable team to empty in its declaration, and to give it new values in the executable part of the block. For an example of a procedure that prints a varray that might be null, see Example Data Type Compatibility. You can assign a collection to a collection variable only if they have the same data type. Having the same element type is not enough. Collection variables group1 and group2 have the same data type, triplet , but collection variable group3 has the data type trio.
The assignment of group1 to group2 succeeds, but the assignment of group1 to group3 fails. To a varray or nested table variable, you can assign the value NULL or a null collection of the same data type. Either assignment makes the variable null. The elements of the two nested tables must have comparable data types. The SQL SET function takes a nested table argument and returns a nested table of the same data type whose elements are distinct the function eliminates duplicate elements.
Although a collection has only one dimension, you can model a multidimensional collection with a collection whose elements are collections. In this example, nva is a two-dimensional varray—a varray of varrays of integers. In this example, ntb1 is a nested table of nested tables of strings, and ntb2 is a nested table of varrays of integers.
In this example, aa1 is an associative array of associative arrays, and ntb2 is a nested table of varrays of strings. To determine if one collection variable is less than another for example , you must define what less than means in that context and write a function that returns TRUE or FALSE.
You cannot compare associative array variables to the value NULL or to each other. Except for Comparing Nested Tables for Equality and Inequality , you cannot natively compare two collection variables with relational operators.
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