Queries

Perform more complex queries by learning essential query keywords and functionality

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Key Concepts

Review core concepts you need to learn to master this subject

SELECT Statement

AS Clause

DISTINCT Clause

WHERE Clause

LIKE Operator

_ Wildcard

% Wildcard

NULL Values

`SELECT` Statement

SELECT *
FROM movies;

The SELECT * statement returns all columns from the provided table in the result set. The given query will fetch all columns and records (rows) from the movies table.

Queries

Lesson 1 of 1

1
Introduction
In this lesson, we will be learning different SQL commands to query a single table in a database. One of the core purposes of the SQL language is to retrieve information stored in a database. …
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2
Select
Previously, we learned that SELECT is used every time you want to query data from a database and * means all columns. Suppose we are only interested in two of the columns. We can select individu…
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3
As
Knowing how SELECT works, suppose we have the code below: SELECT name AS ‘Titles’ FROM movies; Can you guess what AS does? AS is a keyword in SQL that allows you to rename a column or table u…
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4
Distinct
When we are examining data in a table, it can be helpful to know what distinct values exist in a particular column. DISTINCT is used to return unique values in the output. It filters out all dup…
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5
Where
We can restrict our query results using the WHERE clause in order to obtain only the information we want. Following this format, the statement below filters the result set to only include top rate…
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6
Like I
LIKE can be a useful operator when you want to compare similar values. The movies table contains two films with similar titles, ‘Se7en’ and ‘Seven’. How could we select all movies that start w…
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7
Like II
The percentage sign % is another wildcard character that can be used with LIKE. This statement below filters the result set to only include movies with names that begin with the letter ‘A’: SELEC…
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8
Is Null
By this point of the lesson, you might have noticed that there are a few missing values in the movies table. More often than not, the data you encounter will have missing values. Unknown values a…
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9
Between
The BETWEEN operator is used in a WHERE clause to filter the result set within a certain range. It accepts two values that are either numbers, text or dates. For example, this statement filters …
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10
And
Sometimes we want to combine multiple conditions in a WHERE clause to make the result set more specific and useful. One way of doing this is to use the AND operator. Here, we use the AND operat…
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11
Or
Similar to AND, the OR operator can also be used to combine multiple conditions in WHERE, but there is a fundamental difference: - AND operator displays a row if all the conditions are true. - …
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12
Order By
That’s it with WHERE and its operators. Moving on! It is often useful to list the data in our result set in a particular order. We can sort the results using ORDER BY, either alphabetically or…
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13
Limit
We’ve been working with a fairly small table (fewer than 250 rows), but most SQL tables contain hundreds of thousands of records. In those situations, it becomes important to cap the number of rows…
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14
Case
A CASE statement allows us to create different outputs (usually in the SELECT statement). It is SQL’s way of handling if-then logic. Suppose we want to condense the ratings in movies to three le…
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15
Review
Congratulations! We just learned how to query data from a database using SQL. We also learned how to filter queries to make the information more specific and useful. Let’s summarize: - SELECT i…
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