SQL (Structured Query Language ) is language created for querying from database.
Assume you have a database. You want to insert new stuff, update it, select some stuff or maybe delete it overtime.
Easy explained, the database consists of several tables, for example table of students:
id | name | surname | date_of_birth | has_bicycle |
1 | John | Smith | 1995/05/15 | true |
2 | Alex | Hunnybun | 2004/01/19 | false |
3 | Carol | Gladden | 2005/10/13 | true |
The first column is unique id of record in the table (it is not number of the row as we can delete second row and row with id 3 will be second then).
Let’s start with selection. The basic syntax is:
/* comment in sql */
/* basic syntax ended with ; */ SELECT columns FROM table;
/* examples */
/* 1 */ SELECT id FROM students;
/* 2 */ SELECT name, surname FROM students;
/* 3 */ SELECT id, name, surname, date_of_birth, has_bicycle FROM students;
/* 4 */ SELECT * FROM students;
The first query SELECT id FROM students will return whole column with ids. The last 2 queries are the same, * character means everything (every column). The result of query number 2 will be:
name | surname |
John | Smith |
Alex | Hunnybun |
Carol | Gladden |