Joins are used to retrieve rows from two or more tables, based on a related column between those tables.įor example : SELECT e.empno as employee_id, e.ename as employee_name, d.dname as department_name, d. This can be done using JOIN methods, or you can use a second SELECT statement inside your main SELECT query-a subquery. To retrieve information from more than one table, you need to join those tables together. We can use ‘AS’ for alias or used to assign temporarily a new name to a table column.įor example : SELECT empno as employee_id, ename as employee_name, job as job_title To retrieve specific information from a single table, we can simply define the specific column names and apply conditions for the table : To retrieve all the information from single table you can use the following format : Retrieving methods from database From a single table Note: You can get sample table structures along with data which is used in throughout the article from the link below: : optional parameters used for any further restrictions on the data. : the tables from which to retrieve the data. : specifies the column names that need to be retrieved from that particular table or tables. The SELECT statement can be divided into three main parts: To retrieve data from any specific table, we have to use the SELECT statement. Data can be stored in the following hierarchy : PostgreSQL is based on the Relational Database Management System (RDBMS). In this tutorial, we have introduced you to the chinook SQLite sample database and showed you how to connect to it using the sqlite3 tool.SUMMARY: This article covers the SELECT statement in PostgreSQL and how to use it to query data from single and multiple tables: tablesĬustomers invoice_items playlist_track Code language: SQL (Structured Query Language) ( sql ) tables to view all the tables available in the sample database. You should see the following command: sqlite> Code language: Shell Session ( shell ) c:\sqlite>sqlite3 c:\sqlite\db\chinook.db Code language: Shell Session ( shell ) Second, use the following command to connect to the chinook sample database located in the db folder, which is a subfolder of the sqlite folder. If you don’t have zip software installed, you can download a free zip software such as 7-zip.įirst, use the command line program and navigate to the SQLite directory where the sqlite3.exe file is located: c:\sqlite> Code language: Shell Session ( shell ) The sample database file is ZIP format, therefore, you need to extract it to a folder, for example, C:\sqlite\db. Follow us on Facebook and Twitter for latest update. In case you want to have the database diagram for reference, you can download both black
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