Impala CREATE VIEW Statement – Complex & Security Consideration

While it comes to create a view in Impala, we use Impala CREATE VIEW Statement. There is much more to learn about Impala CREATE VIEW Statement. So, let’s learn about it from this article. Apart from its introduction, it includes its syntax, type as well as its example, to understand it well.

Impala CREATE VIEW Statement

Basically, to create a shorthand abbreviation for a more complicated query, we use Impala CREATE VIEW Statement. However, this query can include joins, expressions, reordered columns, column aliases, and other SQL features. This involvement makes a query hard to understand or maintain.

To be more specific, it is purely a logical construct (an alias for a query) with no physical data behind it.
In other words, we can say a view is nothing more than a statement of Impala query language.

That is stored in the database with an associated name. In addition, it is a composition of a table in the form of a predefined SQL query.

Moreover, it carries all the rows of a table or selected ones. It is possible to create it from one or many tables.
There are following options, views offer to users −

• To structure data in a way that users or classes of users find them natural or intuitive.
• Also, restrict access to the data. Like a user can see and modify exactly what they need and no more.
• To generate reports, we can summarize data from various tables, with View.

a. Syntax of CREATE View Statements 

So, the syntax for using Impala CREATE VIEW Statement is-

CREATE VIEW [IF NOT EXISTS] view_name [(column_list)]
AS select_statement

b. Statement type

Impala CREATE VIEW Statement is of DDL Type.

c. Usage of CREATE View Statements

There are several conditions, in which Impala CREATE VIEW statement can be very useful, such as:

• While we want to turn even the most lengthy and complicated SQL query into a one-liner we can use it. For that, we can issue simple queries against the view from applications, scripts, or interactive queries in impala-shell.

For example:

CREATE VIEW [IF NOT EXISTS] view_name [(column_list)]
 AS select_statement

Note The more benefit there is to simplify the original query if it is more complicated and hard-to-read.

• In order to hide the underlying table and column names or to minimize maintenance problems if those names change we re-create the view using the new names, and all queries that use the view rather than the underlying tables keep running with no change.
• While we want to make the optimized queries available to all applications or we want to experiment with optimization techniques we use them.
• Also, when we need to simplify a whole class of related queries. Especially complicated queries involving joins between multiple tables, complicated expressions in the column list, and another SQL syntax that makes the query difficult to understand and debug.

Moreover, we can use the WITH clause as an alternative to creating a view for queries that require repeating complicated clauses over and over again. Like in the select list, ORDER BY, and GROUP BY clauses.

d. Cancellation

It is not possible to cancel it. That implies it Cannot be canceled.

e. HDFS permissions

However, we do not require any HDFS permissions since this statement does not touch any HDFS files or directories.

Complex Type Considerations

We typically use join queries to refer to the complex values, if our tables contain any complex type columns. Such as ARRAY, STRUCT, or MAP.

Also, to hide the join notation, making such tables seem like traditional denormalized tables, and making those tables queryable by business intelligence tools that do not have built-in support for those complex types, we can use views.

However, make sure we cannot directly issue SELECT col_name against a column of complex type. Also, it is not possible to use a view or a WITH clause to “rename” a column by selecting it with a column alias.

Security Considerations in Impala Create View 

Basically, Impala can redact sensitive information when displaying the statements in log files and other administrative contexts if these statements contain any sensitive literal values. Like credit card numbers or tax identifiers.

Examples of Create View in Impala 

For example:

-- Create a view that is exactly the same as the underlying table.
create view v1 as select * from t1;
-- Create a view that includes only certain columns from the underlying table.
create view v2 as select c1, c3, c7 from t1;
-- Create a view that filters the values from the underlying table.
create view v3 as select distinct c1, c3, c7 from t1 where c1 is not null and c5 > 0;
-- Create a view that that reorders and renames columns from the underlying table.
create view v4 as select c4 as last_name, c6 as address, c2 as birth_date from t1;
-- Create a view that runs functions to convert or transform certain columns.
create view v5 as select c1, cast(c3 as string) c3, concat(c4,c5) c5, trim(c6) c6, "Constant" c8 from t1;
-- Create a view that hides the complexity of a view query.
create view v6 as select t1.c1, t2.c2 from t1 join t2 on t1.id = t2.id;

Afterward, to create a series of views and then drop them, see the example below. Basically, how views are associated with a particular database, we can understand with this example.

Also, both the view definitions and the view names for CREATE VIEW and DROP VIEW can refer to a view in the current database or a fully qualified view name.

For example:

-- Create and drop a view in the current database.
CREATE VIEW few_rows_from_t1 AS SELECT * FROM t1 LIMIT 10;
DROP VIEW few_rows_from_t1;
-- Create and drop a view referencing a table in a different database.
CREATE VIEW table_from_other_db AS SELECT x FROM db1.foo WHERE x IS NOT NULL;
DROP VIEW table_from_other_db;
USE db1;
-- Create a view in a different database.
CREATE VIEW db2.v1 AS SELECT * FROM db2.foo;
-- Switch to the other database and drop the view.
USE db2;
DROP VIEW v1;
USE db1;
-- Create a view in a different database.
CREATE VIEW db2.v1 AS SELECT * FROM db2.foo;
-- Drop a view in the other database.
DROP VIEW db2.v1;

So, this was all in Impala Create View Statements. Hope you like our explanation.

Conclusion – Impala Create View Statements

As a result, we have seen the whole concept of Impala CREATE VIEW Statement. Still, if any doubt occurs in how to create the view in Impala, feel free to ask in the comment section.