Basic SQL

You are starting on an exciting path with plenty of new concepts, especially If you are new to the world of databases. Get ready to discover a language that is simple to learn, but at the same time very powerful for querying the database. In this tutorial you use SQL to query databases. A database query is an expression written in SQL language that describes the data you want to obtain from the database. For example, you could write an SQL query to return the names and emails of customers who have not sent orders for more than 6 months.

This article covers two new SELECT clauses:

In this lesson we cover the types of conditions you can put in the [WHERE clause](/sql-tutorial/basic-sql/sql-select-from-where-statement/) of any [SQL SELECT query](/sql-tutorial/basic-sql/sql-select-from-where-statement/). There are several combinations based on the comparison operator and the data type of the columns in the operation.

In this lesson we cover more complex filters than those you learned in [Using The WHERE Clause With Comparison Operators](/sql-tutorial/basic-sql/sql-where-comparison-operators) by using logical operators like `AND`, `OR` and `NOT`.

In this lesson we explore more complex filtering operators than those covered in the previous lessons: [SQL logical operators](/sql-tutorial/basic-sql/sql-where-logical-operators) and [SQL comparison operators](/sql-tutorial/basic-sql/sql-where-comparison-operators).

In this lesson we cover the `NULL` value concept and the SQL `IS NULL` operator. Both are simple but powerful concepts to add into your set of SQL tools. Continue learning new SQL concepts to create more complex `WHERE` conditions.

A SQL _data type_ defines a set of valid values for a given column. In a SQL database, every table column has a data type.

The SQL `CASE` clause can be used in `SELECT`, `DELETE`, `UPDATE` and even in the `INSERT` statement. In SQL, use columns in many different clauses like the `WHERE`, the `SELECT` list, the `ORDER BY`, or the [GROUP BY](/sql-tutorial/intermediate-sql/sql-group-by-clause/). What about the cases where the data is not coming from the same column?