How to query table fields in oracle

Oracle is a relational database management system, and querying table fields is one of the most basic operations of the Oracle database. This article will introduce you to the knowledge about how Oracle queries table fields and help you better manage and operate the database.

1. Use the SELECT statement to query table fields

The SELECT statement is one of the most commonly used statements in Oracle. It can be used to query the data and table structure in the table. When querying table fields, we can use the following statement:

SELECT column1, column2, column3, ... FROM table_name;

Among them, column1, column2, column3, etc. represent the field names in the table, and multiple field names are separated by commas. table_name represents the name of the data table to be queried.

For example, if we want to query the three fields employee_id, first_name and last_name in the employees table, we can use the following statement:

SELECT employee_id, first_name, last_name FROM employees;

The query results are as shown below:

II . Use the DESC command to query table fields

In addition to using the SELECT statement, we can also use the DESC command to query table fields. The DESC command can query the detailed structure information of the table, including table name, column name, data type, length, default value, etc.

The usage method is as follows:

DESC table_name;

Among them, table_name represents the name of the data table to be queried.

For example, if we want to query the detailed field information of the employees table, we can use the following command:

DESC employees;

The query results are as shown below:

3. Use the USER_TAB_COLUMNS table to query the table Field

USER_TAB_COLUMNS is a table that comes with the Oracle database. This table records detailed field information of all tables created by users. We can obtain the field information of a certain table by querying the information of the USER_TAB_COLUMNS table.

The usage is as follows:

SELECT column_name, data_type, data_length, nullable FROM user_tab_columns WHERE table_name='your_table_name';

Among them, column_name represents the field name, data_type represents the field data type, data_length represents the field data length, and nullable represents whether the field can be empty. your_table_name represents the name of the data table to be queried.

For example, if we want to query all field information in the employees table, we can use the following command:

SELECT column_name, data_type, data_length, nullable FROM user_tab_columns WHERE table_name='employees';

The query results are as shown below:

Summary

This article introduces three methods of Oracle query table fields, including using the SELECT statement, DESC command and USER_TAB_COLUMNS table. Through these three methods, you can easily query the field information of Oracle database tables and better manage and operate the database.

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