What Is Explain Plan In Db2?

The access path for an SQL statement specifies how Db2 accesses the data that the query specifies. It specifies the indexes and tables that are accessed, the access methods that are used, and the order in which objects are accessed. … Db2 selects the access paths for dynamic SQL statements when the statements are issued.

What are functions in Db2?

A function is an operation denoted by a function name followed by zero or more input values that are enclosed in parentheses. It represents a relationship between a set of input values and a set of result values. The input values to a function are called arguments .

What are predicates in Db2?

A predicate specifies a condition that is true, false, or unknown about a given value, row, or group. The following rules apply to predicates of any type: Predicates are evaluated after the expressions that are operands of the predicate. All values that are specified in the same predicate must be compatible.

What is Stage 1 predicates DB2?

Stage 1 page range screening predicates refer to partitioning columns are applied to limit the number of partitions that are accessed. Other stage 1 predicates are applied to the data, after data page access. The stage 2 predicates are applied on the returned data rows.

What are mandatory components of DB2?

The complex DB2 internal structure has been divided into 5 major components / Address Spaces:

  • System Services component / System Services Address Space (Job: DSN1MSTR)
  • Locking Services component/ Locking Services Address Space (Job: IRLMPROC)
  • Database Services component/ Database Services Address Space (DSN1DBM1)

What is VARCHAR in DB2?

Db2 VARCHAR type is used to store variable-length character strings. To define a variable-length character string column, you use the following syntax: column_name VARCHAR(n) In this syntax, n is a positive integer that represents the maximum length of n bytes that the column can store.

How do I merge two columns in DB2?

The DB2 CONCAT function will combine two separate expressions to form a single string expression.


What is column function in DB2?

The DB2 COLUMN functions are also known as aggregate functions. … These functions take the values from a particular column of multiple rows and return a single value.

What is Reorg and Runstats in DB2?

runstats is for collecting indexes and tables statistics information which to enable the DB2 optimizer to generate efficient access plan. reorgs is for reorganizing tables and indexes.

What is Sqlca in DB2?

SQLCA. SQLCA is a SQL communication area through which DB2 passes the feedback of SQL execution to the program. It tells the program whether an execution was successful or not. There are a number of predefined variables under SQLCA like SQLCODE which contains the error code.

What is image copy in DB2?

The image copy allows us to download or copy the DB2 table into a mainframe dataset. There are two types of Image copy i.e. Full image copy and Incremental image copy. The full image copy is used to take the backup of the entire table. The incremental image copy refers to the differential backup.

What is Runstats Db2?

RUNSTATS is a DB2 utility that scans a table space or indexes to gather information about space utilization and index efficiency. The information gathered is stored in the DB2 system tables and used by the SQL optimizer to select the best access paths during the bind process.

What is Db2 package and plan?

A package contains control structures that Db2 uses when it runs SQL statements. An application plan relates an application process to a local instance of Db2 and specifies processing options. Packages are produced during program preparation.

How do I create a Db2 plan?

To create a plan table:

  1. On the DB2 Administration Menu (ADB2) panel, specify option E , and press Enter.
  2. On the EXPLAIN (ADB2E) panel, specify the following options, and press Enter: In the command line, specify CT . …
  3. On the Create PLAN_TABLE (ADB2EC) panel, accept the default values, or specify your own values:

What is coalesce in DB2?

COALESCE DB2 function returns the first non-null value in a list of input expressions. This function takes a comma separated list of arguments which are evaluated in the order in which they are specified and returns the first non-NULL value found.

What is IBM DB2 used for?

DB2 is a database product from IBM. It is a Relational Database Management System (RDBMS). DB2 is designed to store, analyze and retrieve the data efficiently. DB2 product is extended with the support of Object-Oriented features and non-relational structures with XML.

Is null DB2 SQL?

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. … If the value is -2 then the column was set to null as the result of a data conversion error.

How does cursor work in Db2?

DB2 uses a cursor to make the rows, from the results table, available to the application program. A cursor identifies the current row of the results table. When you use a cursor, the program can retrieve each row sequentially from the results table until end-of-data (i.e the not found condition SQLCODE=100).

What are the datatypes in Db2?

How Db2 compares values of different data types

  • String data types. Db2 supports several types of string data: character strings, graphic strings, and binary strings.
  • Numeric data types. …
  • Date, time, and timestamp data types. …
  • XML data type. …
  • Large object data types. …
  • ROWID data type. …
  • Distinct types.

What are Db2 locks?

A database lock is a mechanism utilized by Db2 to govern the access to a database object amongst different transactions. The following is a list of objects that Db2 usually regulates via the usage of locks: – Table. – Table partition.

What is thread in Db2?

A thread is a structure that describes a connection made by an application and traces its progress in the Db2 subsystem. … Distributed database access threads (sometimes called DBATs) are threads that are connected through a network to access data at a Db2 server on behalf distributed requesting systems.

What is index in Db2?

Index is a set of pointers, which can refer to rows in a table, blocks in MDC or ITC tables, XML data in an XML storage object that are logically ordered by the values of one or more keys. It is created on DB2 table columns to speed up the data access for the queries, and to cluster and partition the data efficiently.

What is address space in Db2?

The database services address space is responsible for accessing relational databases controlled by Db2 for z/OS and provides most database-related services. The input and output to database resources is performed on behalf of SQL application programs in this address space.