Joining Tables in SQL Without the JOIN Keyword
As someone who is getting into database development, you’ve probably heard of the JOIN keyword in SQL. Joining tables is fundamental in database design, and it comes in handy when you need to fetch data from multiple tables.
But did you know that you can perform the same operation without using the JOIN keyword? In this article, we are going to delve into two alternative methods of joining tables in SQL.
Method 1: Using Comma in FROM Clause and WHERE for Joining Condition
The comma is one of the most fundamental SQL operators. It is used to separate items in a list, and in SQL, it separates columns and table names in the FROM clause.
The first method for joining tables in SQL without using the JOIN keyword involves using the comma in the FROM clause and the WHERE clause to specify the joining condition. Suppose we have two tables, `customers` and `orders`, and we need to get a list of customers who have placed orders.
The two tables have a common column, which is `customer_id`. Here’s how we can join the two tables using the comma:
“`
SELECT *
FROM customers, orders
WHERE customers.customer_id = orders.customer_id;
“`
In this example, we specified the tables we wanted to join in the FROM clause and separated them with a comma.
We also specified the joining condition in the WHERE clause, where we used the common column in both tables, `customer_id`. Why use this method of joining tables?
– It is simple and easy to understand, especially for beginners who may not be too familiar with the JOIN keyword. – In some cases, it may provide better performance than using the JOIN keyword, especially when joining small tables.
However, there are a few caveats to using this method:
– It can be confusing when joining more than two tables. – If the joining condition is not specified correctly, we can get cross-join results that can slow down the performance of queries.
Method 2: Using UNION / UNION ALL
The second method for joining tables in SQL without using the JOIN keyword involves using the UNION or UNION ALL operators. These operators are set operators that combine the results of two or more SELECT statements into a single result set.
Suppose we have two tables, `employees1` and `employees2`, which have the same structure, and we need to get a list of all employees in both tables. Here’s how we can use UNION to achieve this:
“`
SELECT *
FROM employees1
UNION
SELECT *
FROM employees2;
“`
In this example, we used two SELECT statements separated by the UNION operator to combine the results into a single result set. The UNION operator returns distinct rows from both SELECT statements, which means that any duplicate rows are eliminated.
We can also use the UNION ALL operator to combine the results of two or more SELECT statements, including duplicate rows. Here’s how it works:
“`
SELECT *
FROM employees1
UNION ALL
SELECT *
FROM employees2;
“`
The use of UNION ALL combines the results of both SELECT statements, including duplicate rows. Why use this method of joining tables?
– It is useful when joining tables that have different structures. – We can combine any number of SELECT statements using the UNION and UNION ALL operators.
– The use of the UNION operator eliminates duplicate rows from the result set, which can be useful in some cases. However, there are a few caveats to using this method:
– It can be tricky to find the right SELECT statements to combine, especially when dealing with large tables.
– The UNION operator can be slower than using the JOIN keyword, especially when joining large tables.
Syntax for Method 1
If you want to use Method 1 to join tables in SQL, here’s the syntax:
“`
SELECT *
FROM table1, table2, …, tablen
WHERE table1.column = table2.column AND table2.column = … AND tablen.column = table1.column;
“`
In this syntax, we specified the tables to join in the FROM clause, where we separated them with a comma.
We also specified the joining condition in the WHERE clause, where we used the common columns in each table.
Conclusion
Joining tables in SQL is fundamental in database design. While the JOIN keyword is the primary method for joining tables, there are alternative methods that you can use.
In this article, we discussed two alternative methods of joining tables in SQL without using the JOIN keyword. The first method involves using the comma in the FROM clause and the WHERE clause to specify the joining condition, while the second method involves using the UNION or UNION ALL operators to combine the results of SELECT statements.
By using these alternative methods of joining tables, you can write more efficient SQL code and solve complex database problems.
Joining Tables in SQL Without the JOIN Keyword: Examples and Queries
In the previous section, we discussed two alternative methods for joining tables in SQL without using the JOIN keyword. In this section, we will provide examples and queries for both methods.
Method 1: Using Comma in FROM Clause and WHERE for Joining Condition
Let’s illustrate this method using the example of joining an `artist` table and an `album` table. The `artist` table contains information about different music artists, such as their names, and unique artist IDs, while the `album` table contains data about different albums, such as their titles, release dates, and album IDs. The two tables have a common column, which is `artist_id`.
Our goal is to join the two tables based on the `artist_id` column. To join these two tables using Method 1, we can use the following SELECT statement:
“`
SELECT artist.name, album.title
FROM artist, album
WHERE artist.artist_id = album.artist_id;
“`
In this example, we specified the two tables to join in the FROM clause, separating them by a comma.
We then specified the joining condition in the WHERE clause, where we used the common column, `artist_id`, in both tables. Once we execute this query, we will get a result set that lists the names of artists and the titles of their albums, as shown below:
| Name | Title |
|—————-|—————————–|
| Adele | 19 |
| Adele | 21 |
| Maroon 5 | Songs about Jane |
| Maroon 5 | It won’t be soon before long|
| Taylor Swift | Fearless |
| Taylor Swift | Speak now |
This query retrieved the names of the artists and their album titles, effectively joining the `artist` and `album` tables.
Query for Method 1
To perform this method of joining tables, you can use the following query:
“`
SELECT column_name(s)
FROM table1, table2, …, tablen
WHERE table1.column = table2.column AND table2.column = … AND tablen.column = table1.column;
“`
In this query, you can specify the columns you want to retrieve in the SELECT statement and the tables to join in the FROM clause, separating them with a comma.
You then specify the joining condition in the WHERE clause, where you use the common columns in each table to join them. Method 2: Using UNION / UNION ALL
Let’s illustrate the second method using the example of joining two tables that have different structures.
Suppose we have two tables, `employee_info` and `employee_salaries`, with different columns. The `employee_info` table contains information about employees, such as their names, age, and job titles, while the `employee_salaries` table contains data about their salaries, such as their salary amounts and pay scales.
Our goal is to combine these two tables to get a single result set. To join these two tables using Method 2, we can use the following SELECT statement:
“`
SELECT name, age, job_title, salary_amount
FROM employee_info
UNION
SELECT NULL, NULL, NULL, salary_amount
FROM employee_salaries;
“`
In this example, we used UNION to combine the results of two SELECT statements, each retrieving different columns from the two tables. The columns in each SELECT statement must be the same in number and type.
The NULL keywords are placeholders for the missing columns in the second SELECT statement. Once we execute this query, we will get a result set that lists the name, age, job title, and salary amount of each employee, as shown below:
| Name | Age | Job Title | Salary Amount |
|——-|—–|—————–|—————|
| John | 28 | Senior Engineer | 7000.00|
| Mary | 33 | Manager | 10000.00|
| Peter | 25 | Junior Engineer | 5000.00|
| | | | 9000.00|
| | | | 8000.00|
Note that the first three rows correspond to the `employee_info` table, while the last two rows correspond to the `employee_salaries` table.
Query for Method 2
To perform this method of joining tables using UNION/UNION ALL, you can use the following query:
“`
SELECT column_name(s)
FROM table1
UNION / UNION ALL
SELECT column_name(s)
FROM table2;
“`
In this query, you can specify the columns you want to retrieve in each SELECT statement. The UNION operator combines the results of both SELECT statements, returning distinct rows, while UNION ALL combines the results, including duplicate rows.
Conclusion
In conclusion, the JOIN keyword is the primary method for joining tables in SQL, but there are alternative methods that you can use as well. The first method involves using the comma in the FROM clause and the WHERE clause to specify the joining condition, while the second method involves using the UNION or UNION ALL operators to combine the results of SELECT statements.
Each method has its own advantages and disadvantages, depending on the specific needs of your query and database design. With a little practice, you can become proficient in using both the JOIN keyword and these alternative methods when joining tables in SQL.
Joining Tables in SQL Without the JOIN Keyword: Results and Syntax
In the previous sections, we discussed two alternative methods of joining tables in SQL without using the JOIN keyword. In this section, we will explore the results and syntax of these methods in more detail.
Method 1: Using Comma in FROM Clause and WHERE for Joining Condition
Let’s continue with the example of Method 1, where we join the `artist` table and the `album` table based on the common `artist_id` column. Suppose we want to retrieve additional information about the albums, such as the recording year and the musicians who contributed to them.
We can modify our previous query to include these additional columns as follows:
“`
SELECT artist.name, album.title, album.recording_year, album.musicians
FROM artist, album
WHERE artist.artist_id = album.artist_id;
“`
In this example, we added two new columns from the `album` table, `recording_year` and `musicians`, to our result set. Once we execute this query, we will get a combined result set that includes information from both tables.
| Name | Title | Year | Musicians |
|—————-|—————————–|——|————————————————–|
| Adele | 19 | 2008 | Adele Adkins |
| Adele | 21 | 2011 | Adele Adkins |
| Maroon 5 | Songs about Jane | 2002 | Adam Levine, Jesse Carmichael, Ryan Dusick |
| Maroon 5 | It won’t be soon before long| 2007 | Adam Levine, Jesse Carmichael, Mickey Madden, etc|
| Taylor Swift | Fearless | 2008 | Taylor Swift |
| Taylor Swift | Speak now | 2010 | Taylor Swift |
Notice that the result set includes information from both tables, joined based on the common `artist_id` column.
Syntax for Method 1
The syntax for Method 1 is straightforward, as we can see below:
“`
SELECT column_name(s)
FROM table1, table2, …, tablen
WHERE table1.column = table2.column AND table2.column = … AND tablen.column = table1.column;
“`
In this syntax, we can specify the columns we want to retrieve in the SELECT statement, followed by a list of tables separated by commas.
We then use the WHERE clause to specify the joining condition, where we use the common column in both tables. Method 2: Using UNION / UNION ALL
Now let’s consider the syntax for Method 2.
Suppose we have two tables, `table1` and `table2`, with different structures. We can use the following syntax to join the tables:
“`
SELECT matching columns
FROM table1
UNION / UNION ALL
SELECT matching columns
FROM table2;
“`
In this syntax, we can specify the matching columns we want to retrieve in each SELECT statement, making sure that they have the same data types. We then use the UNION or UNION ALL operator to combine the results of both SELECT statements.
For example, suppose we have two tables, `clients_2019` and `clients_2020`, with different structures:
`clients_2019`:
| ID | Name | Email | Category |
|——|——-|—————|———|
| 1001 | John | [email protected]| A |
| 1002 | Mary | [email protected]| B |
| 1003 | Peter | [email protected]| A |
`clients_2020`:
| ID | Name | Email | Category |
|——|——-|——————–|———|
| 2001 | Alice | [email protected] | A |
| 2002 | Bob | [email protected] | C |
| 2003 | John | [email protected] | A |
We can use Method 2 to retrieve a list of all clients, combining the data from both tables:
“`
SELECT ID, Name, Email, Category
FROM clients_2019
UNION
SELECT ID, Name, Email, Category
FROM clients_2020;
“`
The result set will include all clients from both tables, as shown below:
| ID | Name | Email | Category |
|——|——-|——————–|———|
| 1001 | John | [email protected] | A |
| 1002 | Mary | [email protected] | B |
| 1003 | Peter | [email protected] | A |
| 2001 | Alice | [email protected] | A |
| 2002 | Bob | [email protected] | C |
| 2003 | John | [email protected] | A |
Note that the UNION operator eliminates the duplicate row of John because it returned only distinct rows while UNION ALL would have kept the duplicates.
Conclusion
In this section, we examined the results and syntax of Method 1 and Method 2. In Method 1, we can join tables by using the comma in the FROM clause and the WHERE clause to specify the joining condition.
In Method 2, we can join tables by using the UNION or UNION ALL operators to combine the results of SELECT statements. In both cases, the syntax is straightforward and easy to understand.
Depending on the structure and requirements of your tables, you can choose the method that is more suitable for your needs. By mastering both methods, you can become more proficient in SQL and improve the efficiency of your queries.
Joining Tables in SQL Without the JOIN Keyword: Method 2 Examples and Queries
In the previous sections, we discussed two alternative methods of joining tables in SQL without using the JOIN keyword. Here, we will explain an example and query for Method 2 using the UNION operator.
Method 2: Using UNION / UNION ALL
Suppose we have two tables, the `customer` table, and the `supplier` table. Both tables contain common data about customers and suppliers, such as their names, addresses, and contact information, but the structure of the tables is slightly different, and there is no common column between them.
Our goal is to combine the data from both tables and return a list of all customers and suppliers. To join these two tables using Method 2 with the UNION operator, we can use the following SELECT statement:
“`
SELECT first_name, last_name, address, phone, email
FROM customer
UNION
SELECT supplier_name AS first_name, ” AS last_name, address, phone, email
FROM supplier;
“`
In this example, we selected five columns from the `customer` table, and five columns from the `supplier` table, each with a different column name. When selecting columns with different names from each table, we can use aliases to make the column names the same.
We also included an empty string as the `last_name` value for the suppliers to match the number of columns and data types. Then, we used the UNION operator to combine the results of