Db2: Show Information

Introduction

This tutorial covers various ways to retrieve information about databases, tables, and other entities in IBM Db2. Displaying information is essential for database administrators and developers to understand the structure and characteristics of the database.

Showing Information in IBM Db2

Syntax

To show information in IBM Db2, you can use SQL queries and administrative commands specific to Db2. Here are some common examples:

-- Show all databases
LIST DATABASES;

-- Show tables in a specific database
SELECT TABNAME FROM SYSCAT.TABLES WHERE TABSCHEMA = 'your_schema';

-- Show columns of a table
SELECT COLNAME, TYPENAME FROM SYSCAT.COLUMNS WHERE TABNAME = 'your_table';

-- Show indexes on a table
SELECT INDNAME, UNIQUERULE FROM SYSCAT.INDEXES WHERE TABNAME = 'your_table';

Example

Consider a scenario where you want to show information about tables and columns in a specific database:

-- Show tables in the 'sales' schema
SELECT TABNAME FROM SYSCAT.TABLES WHERE TABSCHEMA = 'sales';

-- Show columns of the 'orders' table
SELECT COLNAME, TYPENAME FROM SYSCAT.COLUMNS WHERE TABNAME = 'orders';

Output

The output will include a list of tables in the specified schema and the columns of the specified table, along with their data types.

Explanation

In this example, we use SQL queries against Db2 system catalog tables (SYSCAT.TABLES and SYSCAT.COLUMNS) to retrieve information about tables and columns. Db2 system catalog tables store metadata about the database.

Use

• Database Administration: Database administrators use information queries to understand the structure of the database and optimize performance.
• Developers: Developers use information queries to retrieve details about tables and columns when working with databases in their applications.

Important Points

• Ensure proper permissions to access system catalog tables.
• Db2 provides a set of system catalog tables (SYSCAT schema) for querying metadata.
• Use filters in queries (WHERE clauses) to narrow down the information based on your needs.

Summary

Showing information in IBM Db2 is a fundamental aspect of database management and development. By querying system catalog tables, you can retrieve valuable metadata about databases, tables, columns, and other entities. This information is crucial for understanding the structure of the database and making informed decisions during database administration and development.