Data in oracle query table

Oracle database is a very popular relational database management system that can store and manage data. In Oracle, data is stored in tables, and querying tables can obtain the desired data. This article will introduce in detail how to query table data in Oracle databases.

1. Understand the Oracle table

The Oracle table is a two-dimensional table, which consists of several columns and several rows. Each column has its own field name and data type. Each row contains a record, called "row data".

In Oracle, tables can be created through SQL statements. For example, use the following SQL statement to create a table named employee:

CREATE TABLE employee (
  id        NUMBER(10) PRIMARY KEY,
  name      VARCHAR2(50),
  age       NUMBER(3),
  salary    NUMBER(10,2),
  hire_date DATE
);

This statement creates a table named employee and defines 5 columns (id, name, age, salary, and hire_date). Columns correspond to different data types.

2. Use the SELECT statement to query table data

Querying table data is one of the most common operations in the Oracle database. Oracle provides the SELECT statement for retrieving data from tables.

The following is an example of a simple SELECT statement:

SELECT * FROM employee;

This statement selects all columns and all rows in the employee table. The results show each row of data in the table.

If you only need to query the data of a specific column, you can use the following SELECT statement:

SELECT id, name, salary FROM employee;

This statement only returns the id, name and salary columns in the employee table.

You can also use the SELECT statement to filter the data in the table. For example, only return information about employees whose salary is greater than 10,000:

SELECT * FROM employee WHERE salary > 10000;

This statement only returns information about employees whose salary is greater than 10,000.

3. Use the ORDER BY statement to sort table data

If you want to sort the query results, you can use the ORDER BY statement. For example, sort by salary from high to low:

SELECT * FROM employee ORDER BY salary DESC;

This statement sorts the data in the employee table from high to low by salary and returns all column and row data.

4. Use the LIKE statement to fuzzy query table data

If you want to fuzzy query the data in the table, you can use the LIKE statement. For example, to search for employees whose names begin with "J":

SELECT * FROM employee WHERE name LIKE 'J%';

This statement will return information about all employees whose names begin with "J".

5. Use the GROUP BY statement to group query table data

If you want to group and summarize the query results, you can use the GROUP BY statement. For example, to display the average salary of employees in units of departments:

SELECT department, AVG(salary) FROM employee GROUP BY department;

This statement calculates the average salary of employees according to departments, and returns the results in units of departments.

6. Use the JOIN statement to jointly query table data

If you need to jointly query data in multiple tables, you can use the JOIN statement. For example, query employee information and department information:

SELECT employee.name, department.name
FROM employee
JOIN department ON employee.department_id = department.id;

This statement jointly queries the employee table and department table, and returns the employee name and department name.

7. Summary

Using the SELECT statement to query data in the Oracle table is one of the most basic operations in the Oracle database. In addition, although common data operations can be completed using the above statements, Oracle database also supports more data operations, such as INSERT, UPDATE, and DELETE operations. By learning the above content, you can become more proficient in operating data in Oracle database tables and better manage your data.

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