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Filter Records

The WHERE clause is used to filter records.

It is used to extract only those records that fulfill a specified condition.

If we want to return only the records where city is London, we can specify that in the WHERE clause:

Example

SELECT * FROM customers
WHERE city = 'London';

Text Fields vs. Numeric Fields

PostgreSQL requires quotes around text values.

However, numeric fields should not be enclosed in quotes:

Example

SELECT * FROM customers
WHERE customer_id = 19;

Quotes around numeric fields will not fail, but it is good practice to always write numeric values without quotes.

Greater than

Use the > operator to return all records where customer_id is greater than 80:

Example

SELECT * FROM customers
WHERE customer_id > 80;

Quotes around numeric fields will not fail, but it is good practice to always write numeric values without quotes.

PostgreSQL Exercises

Test Yourself With Exercises

Exercise:

Write the correct SQL statement to select all records from the customers table where the city value is "Berlin":

SELECT * FROM customers
;

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