SQL Where

What the WHERE clause does

Most tables hold far more data than you need for any single question. The WHERE clause lets you narrow a result set down to just the rows that satisfy a condition you describe. When SQL evaluates a query, it looks at each row, tests it against the condition, and keeps only the rows where the condition is true. Rows that do not match are quietly left out of the result.

SELECT CustomerName, City, Country
FROM Customers
WHERE Country = 'Germany';

In the query above, only customers whose Country column holds the text 'Germany' are returned. Notice that the text value is wrapped in single quotes. In standard SQL, text (string) values are always enclosed in single quotes, while numeric values are written on their own without quotes.

SELECT CustomerName, CustomerID
FROM Customers
WHERE CustomerID = 42;

Comparison operators you can use

The WHERE clause is not limited to checking for an exact match. You can compare values in several ways using the operators below. Each operator returns true or false for every row, and the row is kept only when the result is true.

SELECT ProductName, Price
FROM Products
WHERE Price >= 50;

• The condition after WHERE can reference any column in the table, even columns you are not selecting.
• String comparisons are case-sensitive or case-insensitive depending on your database's collation settings.
• You can combine several conditions in one WHERE clause using AND, OR, and NOT, which are covered in a later lesson.
• WHERE also works with UPDATE and DELETE statements to control exactly which rows are changed or removed.