oracle query primary key

Oracle is a commonly used relational database management system that supports the efficient operation of large enterprise-level applications. When using Oracle to query, it is often necessary to query the primary key of the table to ensure the uniqueness and integrity of the data. This article will introduce how to query the primary key in Oracle.

1. What is a primary key

In a relational database, each table has a primary key, which is used to identify and uniquely distinguish each row of data in the table. The primary key has the characteristics of uniqueness, non-nullity and stability in the table. A primary key can be a single column or a combination of columns, and primary key values ​​cannot be changed or deleted. In Oracle, primary keys are usually created automatically, or they can be created manually using the ALTER TABLE statement.

2. Query the primary key of the table

To query the primary key of the table, you can use the following two methods:

1. Query the ALL_CONS_COLUMNS table

In Oracle , the system automatically generates many tables to store various types of metadata information. ALL_CONS_COLUMNS is such a table, which contains information about all columns, including the table to which the column belongs, the name of the column, the data type of the column, the length of the column, etc. If a column is a primary key, there is corresponding information about that column in the table.

You can use the following query statement to obtain the primary key information of the table from the ALL_CONS_COLUMNS table:

SELECT *
FROM ALL_CONS_COLUMNS
WHERE TABLE_NAME='表名' AND CONSTRAINT_NAME='主键名';

Among them, the table name and primary key name are the names of the table and primary key that need to be queried.

2. Query ALL_CONSTRAINTS table

Another way to query the primary key of a table is to query the ALL_CONSTRAINTS table. The ALL_CONSTRAINTS table contains all constraint information in the Oracle database, including the primary key, unique key, foreign key, etc. of the table.

You can use the following query statement to obtain the primary key information of the table from the ALL_CONSTRAINTS table:

SELECT CONSTRAINT_NAME
FROM ALL_CONSTRAINTS
WHERE TABLE_NAME='表名' AND CONSTRAINT_TYPE='P';

Among them, the table name is the name of the table that needs to be queried. CONSTRAINT_TYPE='P' means querying primary key information.

3. Summary

To query the primary key of a table in Oracle, you can use the ALL_CONS_COLUMNS table or ALL_CONSTRAINTS table. No matter which method is used, you can quickly find the primary key of the table and perform related operations to ensure the integrity and accuracy of the data. At the same time, for programmers facing complex data models, mastering the method of querying primary keys is also an essential skill.

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