SQL – SELECT Database, USE Statement
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To work with a database in SQL, we need to first select the database we want to work with. After selecting the database, we can perform various operations on it such as creating tables, inserting data, updating data, and deleting data.
The USE DATABASE Statement
The SQL USE DATABASE statement is used to select a database from a list of databases available in the system. Once a database is selected, we can perform various operations on it such as creating tables, inserting data, updating data, and deleting data.
Syntax
Following is the syntax of the USE DATABASE statement in SQL −
USE DatabaseName;
Here, the DatabaseName is the name of the database that we want to select. The database name is always unique within the RDBMS.
Example
First of all we will create a database using the following SQL CREATE DATABASE query −
CREATE DATABASE testDB;
Now, we can list all the available databases as follws −
SHOW DATABASES;
The output will be displayed as −
| Database |
|---|
| master |
| performance_schema |
| information_schema |
| mysql |
| testDB |
Example: Select/Switch Database
Following query is used to select/switch the current database to testDB −
USE testDB;
Output
Database changed
Once we finish switching to the database testDB we can perform operations such as creating a table, and inserting data in that table as shown below −.
CREATE TABLE CALENDAR(MONTHS DATE NOT NULL);
Now, let us insert some records in the CALENDAR table using SQL INSERT statements as shown in the query below −
INSERT INTO CALENDAR(MONTHS) VALUES(''2023-01-01'');
INSERT INTO CALENDAR(MONTHS) VALUES(''2023-02-01'');
INSERT INTO CALENDAR(MONTHS) VALUES(''2023-03-01'');
INSERT INTO CALENDAR(MONTHS) VALUES(''2023-04-01'');
INSERT INTO CALENDAR(MONTHS) VALUES(''2023-12-01'');
Let”s verify the operation by listing all the records from CALENDAR table using SQL SELECT statement as shown below −
SELECT * FROM CALENDAR;
Output
The output will be displayed as −
| MONTHS |
|---|
| 2023-01-01 |
| 2023-02-01 |
| 2023-03-01 |
| 2023-04-01 |
| 2023-12-01 |
Selecting a Non Existing Database
An attempt to select a non-existent database will result in an error. In the following query we are trying to switch to the database which does not exist −
Example
USE unknownDatabase;
Output
On executing the above query, the output will be displayed as −
ERROR 1049 (42000): Unknown database ''unknownDatabase''
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