Structured Query Language

Structured Query Language (SQL) is one of the languages used to view or change data in databases. The statements used in this language are called SQL queries.

Basic use of SQL queries is to:

• Get data from the database (the SELECT command)
• Add data to the database (the INSERT command)
• Change data in the database (the UPDATE command)
• Remove data from the database (the DELETE command)
• Set up the database to hold data (the CREATE and ALTER commands)

Examples

This is a simple SQL Query which is used to show all values stored in column named 'my_column' from the data table named 'my_table'.

SELECT my_column FROM my_table;

Here is an example of inserting new information into a table called 'people.' The query first specifies the table as 'people', then the columns in which data is going to be inserted into, and the data that is going into these columns. As a result, data will be added into the columns in the same order the column names are listed in the first brackets: (first_name, last_name, age, favorite_food).

INSERT INTO people (first_name, last_name, age, favorite_food) VALUES ("Bob", "Page", "42", "Hamburgers");

In the example below the columns aren't listed. This would result in an attempt to add the data into the table in the order the values are listed.

INSERT INTO people VALUES ("Bob", "Page", "42", "Hamburgers");

Doing the above (without naming the columns) might result in inputting the data in an incorrect column or the statement might not run correctly - when the value types are mismatched (for example trying to input a word into a column storing only numbers).