Step-by-Step Guide

Here is a step-by-step tutorial to create a table and perform queries in the QueryTool with SQL from scratch regardless of your database (Resources), since SQL is a standard language used to interact with relational databases, and both databases of data follow the SQL conventions and standards:

Step 1: Create a Table

To start, you need to create a table in your database. Let's imagine we want to create a table called "Users" with the columns "ID", "Name", and "Age". We will use the following SQL code to create it.

CREATE TABLE Users (
  ID INT PRIMARY KEY,
  Name VARCHAR(50),
  Age INT
);

In this example, we are defining an "ID" column of type integer (INT) as the primary key (PRIMARY KEY), a column "Name" of type string (VARCHAR) with a maximum length of 50 characters, and a column " Age" of type integer (INT).

Step 2: Insert data into the table

Once you have the table created, you can insert data into it using the INSERT INTO clause. Here is an example to insert a user into the table:

INSERT INTO Users (ID, Name, Age) VALUES (1, 'Juan', 25);

This code will insert a user with ID 1, name "John" and age 25 into the "Users" table.

Step 3: Consult data from the table

Now that you have data in your table, you can perform queries to retrieve specific information. Here are some examples:

• Select all records in the table:

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  SELECT * FROM Users;
  

• Select only the name and age of users over 18 years old:

  SQL

  SELECT Name, Age FROM Users WHERE Age > 18;
  

Step 4: Update records in the table

If you need to update any data in the table, you can use the UPDATE clause. For example, if you want to update the age of a user with ID 1:

UPDATE Users SET Age = 30 WHERE ID = 1;

This will update the age of the user with ID 1 to 30.

Step 5: Delete records from the table

If you want to delete records from the table, you can use the DELETE clause. For example, if you want to remove all users older than 40:

DELETE FROM Users WHERE Age > 40;

This will remove all records from the "Users" table where the age is greater than 40.

Operators and Unions between tables

Comparison operators:

Comparison operators are used in WHERE clauses to set more specific filter conditions. Some examples of comparison operators are:

• Equality (=): selects records that match a specific value.
• Not equal to (!= or <>): Selects records that do not match a specific value.
• Greater than (>), less than (<), greater than or equal to (>=), less than or equal to (<=): select records that meet the established comparison conditions.

Example:

SELECT * FROM Users WHERE Age >= 30;

This query will select all users whose age is greater than or equal to 30.

Logical operators

Logical operators are used to combine conditions in WHERE clauses. The most common operators are:

• AND: selects records that meet all the specified conditions.
• OR: selects records that meet at least one of the specified conditions.
• NOT: reverses the condition.

Example:

SELECT * FROM Users WHERE Age >= 30 AND City = 'Madrid';

This query will select all users whose age is greater than or equal to 30 and who live in the city of Madrid.

Aggregation functions

Aggregation functions are used to perform calculations on sets of data and return a single result. Some common aggregation functions are:

• COUNT: returns the number of selected rows.
• SUM: returns the sum of the values ​​in a column.
• AVG: returns the average of the values ​​in a column.
• MAX: returns the maximum value of a column.
• MIN: returns the minimum value of a column.

Example:

SELECT COUNT(*) AS TotalUsers FROM Users;

This query will return the total number of users in the "Users" table.

Joins / union of two or more tables

Joins allow you to combine data from two or more tables based on a column in common between them. Some common types of joins are:

• INNER JOIN: returns the records that have matches in both tables.
• LEFT JOIN: returns all the records from the left table and the matching records from the right table.
• RIGHT JOIN: returns all the records from the right table and the matching records from the left table.
• FULL JOIN: returns all records when there are matches in any of the tables.

Example:

SELECT Users.Name, Orders.Product
FROM Users
INNER JOIN Orders ON Users.ID = Orders.UserID;

This query will join the "Users" table with the "Orders" table based on the "ID" column of the "Users" table and the "UserID" column of the "Orders" table, returning the name of the user and the product of each order.

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Start with simple queries:

When you're learning SQL, start with simple queries and gradually work your way up to more
complex. This will allow you to better understand the basic syntax and structures of queries before tackling more complicated tasks.

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Break your queries into smaller steps:

If you have a complex query, break it down into smaller steps and test each step separately. This will help you identify any errors or problems in a specific area of ​​the query and make it easier to debug.

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SQL

Remember that these are just basic examples to get started with SQL queries. There are many more advanced operations and features that you can explore as you become more familiar with the language.

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Keep learning with the SingleStore Documentation

You can find more information at SIngleStore.

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Keep learning with the MySQL Documentation

You can find more information in MySQL.