What is explain in Db2 mainframe?

What is explain in Db2 mainframe?

EXPLAIN indicates whether Db2 used an index to access data, whether sorts were performed, whether parallel processing was used, and so on. As you gain experience working with Db2, you can use the plan table to give optimization hints to Db2 that influence access path selection.

What is explain statement in Db2?

The EXPLAIN statement obtains information about access path selection for an explainable statement . A statement is explainable if it is a SELECT, MERGE, TRUNCATE, or INSERT statement, or the searched form of an UPDATE or DELETE statement.

How do I run a Db2 Explain Plan?

Perform the following steps to generate the query plan:

1. Log into DB2 server as instance owner.
2. Ensure that tables exist or just recreate them. Details can be found in DB2 infocenter.
3. Save the problematic SQL statement in a file, for example, sql1.sql .
4. Use the db2exfmt command to generate a query plan:

What is explain table in Db2?

EXPLAIN tables contain information about SQL statements and functions that run on Db2 for z/OS®. You can create and maintain a set of EXPLAIN tables to capture and analyze information about the performance of SQL statements and functions that run on Db2 for z/OS.

What do you need to do before you do explain in DB2?

Before you can use EXPLAIN, you must create a plan table to hold the results of EXPLAIN. Populate the plan table. You can populate the plan table by executing the SQL statement EXPLAIN. You can also populate a plan table when you bind or rebind a plan or package by specifying the option EXPLAIN(YES).

What is DB2 bind process?

The DBRM contains the SQL statements that the DB2 precompiler has extracted from the application program. In the bind process, the SQL statements in the DBRM are put into an operational (“bound”) form, by being translated into the control structures that DB2 uses when it runs SQL statements.

How will you explain query tool?

The Query Tool is a powerful, feature-rich environment that allows you to execute arbitrary SQL commands and review the result set. You can access the Query Tool via the Query Tool menu option on the Tools menu, or through the context menu of select nodes of the Browser tree control.

Which method is used in a DB2 execute query?

executeQuery method. To retrieve data from a table using a SELECT statement with parameter markers, you use the PreparedStatement. executeQuery method.

How do I write a query in DB2?

Db2 SELECT

1. SELECT select_list FROM table_name;
2. SELECT title FROM books;
3. SELECT title, isbn FROM books;
4. SELECT book_id, title, total_pages, rating, isbn, published_date, publisher_id FROM books;
5. SELECT * FROM books;
6. SELECT expression FROM sysibm.sysdummy1;
7. SELECT CURRENT_DATE FROM sysibm.sysdummy1;

What is cursor in Db2?

Db2 has a mechanism called a cursor . Using a cursor is like keeping your finger on a particular line of text on a printed page. In Db2, an application program uses a cursor to point to one or more rows in a set of rows that are retrieved from a table.

What is Db2 error?

The DB2 error states that DB2 failed to insert the new record into the due to a primary key constraint violation. This means that there is already a record in the TI_APGROUP_0 table that has the same CATENTRY_ID value as the record you are attempting to insert.

What is null indicator in Db2?

The null indicator is used by DB2 to track whether its associated column is null or not. A positive value or a value of 0 means the column is not null and any actual value stored in the column is valid.

What is query explain with example?

Query is another word for question. In fact, outside of computing terminology, the words “query” and “question” can be used interchangeably. For example, if you need additional information from someone, you might say, “I have a query for you.” In computing, queries are also used to retrieve information.

What is an explain in DB?

The EXPLAIN keyword is used throughout various SQL databases and provides information about how your SQL database executes a query. In MySQL, EXPLAIN can be used in front of a query beginning with SELECT , INSERT , DELETE , REPLACE , and UPDATE .

What SQL is used in Db2?

Db2 transforms each SQL statement, that is, the specification of a result table, into a sequence of operations that optimize data retrieval. This transformation occurs when the SQL statement is prepared . This transformation is also known as binding . All executable SQL statements must be prepared before they can run.

WHAT IS NULL value in Db2?

A null value is a special value that Db2 interprets to mean that no data is present. If you do not specify otherwise,Db2 allows any column to contain null values. Users can create rows in the table without providing a value for the column.