How to query and create tables in Oracle through SQL language

Oracle query and create tables

Oracle is a relational database, and users can perform data operations through SQL (Structured Query Language) language. In Oracle, the two most commonly used operations are querying and creating tables. This article will introduce how to query and create tables in Oracle through SQL language.

Query data

Querying is an important function of Oracle database. Through queries, you can get the required data and improve data utilization. In Oracle, query statements are implemented using SELECT statements. For example, to query the names and addresses of all customers from a table named "customers", you can use the following statement:

SELECT name, address FROM customers;

If you want to filter the results , you can use the WHERE clause. For example, to query all customers who live in "New York", you can use the following statement:

SELECT name, address FROM customers WHERE address='New York';

It should be noted that, When querying, you must follow the grammatical rules of the SQL language, including case sensitivity, data type matching, etc.

Create table

In Oracle, creating a table is also a very important operation. Table is the basic unit of database, and data is stored in table. In Oracle, create a table using the CREATE TABLE statement. For example, to create a table named "students" that contains students' names, ages, and cities, you can use the following statement:

CREATE TABLE students (
name varchar(50),
age int,
city varchar(50)
);

When creating a table, you need to pay attention to the table naming rules, column data types, column constraints and other factors. It is necessary to ensure that table names and column names are unique to avoid duplication. The data type of the column should match the data type to be stored to avoid data type mismatch. Table constraints can ensure the integrity and consistency of data, including primary key constraints, foreign key constraints, non-null constraints, unique constraints, etc.

It should be noted that before creating a table, you need to create a database first. When creating a table, you need to specify the database to which the table belongs. At the same time, when creating a table, you need to set parameters such as the size and storage location of the table according to the actual situation.

Summary

In Oracle, querying and creating tables are very common operations. Through queries, you can easily obtain the required data and improve data utilization. By creating tables, data can be stored in the database to ensure data security and integrity. You need to follow the grammatical rules of the SQL language. When using queries and creating tables, you need to pay attention to factors such as grammatical specifications, naming rules, and data types. If you can master these operations proficiently, you can use Oracle database more flexibly.

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