Gathering Column Information from Oracle Data Dictionary Views

A core part of managing database objects in Oracle is understanding the structure of each table—its columns, data types, nullability rules, storage characteristics, and statistical properties. Oracle stores this metadata in data dictionary views, which provide a consistent and authoritative way to look inside your schema or across the entire database.

In Oracle 23c/23ai, data dictionary access continues to follow the same core pattern used in earlier releases: use USER_* views to inspect your own objects, ALL_* views to inspect objects you have privileges on, and DBA_* views for full administrative visibility. For table columns specifically, the most important view is USER_TAB_COLUMNS.

USER_TAB_COLUMNS – Core View for Column Metadata

USER_TAB_COLUMNS provides a detailed description of each column in the tables you own. The following list summarizes the most frequently used metadata elements:

These fields allow you to reconstruct the logical structure of your table using only the metadata provided by Oracle’s catalog. They are foundational for schema analysis, report generation, automated code generation, and data governance.

Column Statistics: USER_TAB_COL_STATISTICS

In addition to structural metadata, Oracle maintains column-level statistics in USER_TAB_COL_STATISTICS. These statistics are used by the Cost-Based Optimizer (CBO) to generate efficient execution plans.

Statistical metadata commonly includes:

• Number of distinct values
• Count of NULL values
• Minimum and maximum column values
• Density and histogram information

Modern Oracle databases no longer use the old ANALYZE command for gathering statistics. Instead, statistics are collected automatically or manually using DBMS_STATS. This provides more accurate, efficient, and optimizer-friendly results.

Joining USER_TABLES and USER_TAB_COLUMNS

When gathering information about multiple tables, you often need to combine table-level and column-level metadata. The example below demonstrates joining USER_TABLES with USER_TAB_COLUMNS to list each table and its columns:

SELECT t.table_name,
       c.column_name
FROM   user_tables t
JOIN   user_tab_columns c
       ON t.table_name = c.table_name
ORDER  BY t.table_name, c.column_id;

This returns all tables owned by your user along with their columns, ordered in the same sequence as they appear in the table definition.

Additional Data Dictionary Views for Column Analysis

Beyond the basic views, Oracle provides other useful metadata sources:

• ALL_TAB_COLUMNS – includes columns in tables you have privileges on.
• DBA_TAB_COLUMNS – catalog-wide view for DBAs.
• DBA_TAB_COL_USAGE – indicates how columns are used in predicates and joins, useful for index tuning.
• USER_LOBS – for CLOB/BLOB/JSON and other LOB metadata.

These views allow you to perform everything from schema documentation to impact analysis during development or migration.

Mapping Table Characteristics Across Data Dictionary Views