Join 2 tables in sql without common column
Can You Join Two Tables With Common Column? With Code Examples Show
In this tutorial, we will try to find the solution to Can You Join Two Tables With Common Column? through programming. The following code illustrates this. SELECT s.last_name, s.first_name, FROM enrollment e JOIN student s ON s.id=e.student_id JOIN payment p ON p.course_code=e.course_code AND p.student_id=e.student_id; We have demonstrated, with a plethora of illustrative examples, how to tackle the Can You Join Two Tables With Common Column? problem. Can you join two tables with different columns?Merging tables by columns. Multiple tables can be merged by columns in SQL using joins. Joins merge two tables based on the specified columns (generally, the primary key of one table and a foreign key of the other).13-Sept-2021 There are few ways to combine the two tables without a common column including Cross Join (Cartesian Product) and UNION. This is not a join but can be useful for merging tables in SQL.24-Jan-2022 How do I combine two tables in the same column in SQL?The UNION operator is used to combine the result-set of two or more SELECT statements.
How do you associate two tables together?The join is done by the JOIN operator. In the FROM clause, the name of the first table ( product ) is followed by a JOIN keyword then by the name of the second table ( category ). This is then followed by the keyword ON and by the condition for joining the rows from the different tables.16-Sept-2020 How do I join two tables with the same column names?When two tables use the same column name(s), use table_name. column_name or table_alias. column_name format in SELECT clause to differentiate them in the result set. Use INNER JOIN whenever possible because OUTER JOIN uses a lot more system resources and is much more slower. How can I join two tables without joining?How to Join Tables in SQL Without Using JOINs
Can two tables without primary key?A primary key is not required. A foreign key is not required either. You can construct a query joining two tables on any column you wish as long as the datatypes either match or are converted to match.24-Apr-2011 Does join table need primary key?A table must have exactly one primary key to qualify as relational, but that key can be composed of multiple columns. A foreign key, by contrast, is one or more fields or columns that corresponds to the primary key of another table. Foreign keys are what make it possible to join tables to each other.18-Jun-2018 What is the difference between join and UNION?There is a major difference between JOIN and UNION in SQL. Using the JOIN clause, we combine the attributes of two given relations and, as a result, form tuples. Whereas we use the UNION clause when we want to combine the results obtained from two queries. They both combine data differently. How do I join two tables vertically in SQL?SQL UNION combines two separate SQL queries into one result set. A JOIN statement adds additional table columns to a result set (horizontally), UNION combines row results from one table with rows of another table (vertically). In order to perform a UNION the columns of table 1 must match those of table 2. This article discusses about merging multiple tables by rows and columns using SQL along with a few examplesImage by authorIn practice, it is very rare to have an SQL query involving a single table. We may need to merge multiple tables by rows (records) or columns (fields) to get the desired result. In this article, we’ll discuss the operators/commands in SQL that enable use to merge tables by rows or columns. Merging tables by columnsMultiple tables can be merged by columns in SQL using joins. Joins merge two tables based on the specified columns (generally, the primary key of one table and a foreign key of the other). Below is the generic syntax of SQL joins. SELECT In the above syntax, table_1 and table_2 are the two tables with the key column (matching column in both the tables), id. We use the keyword USING only when the key column has the same name in both the tables. Otherwise, we need to explicitly mention the key columns of both the tables as shown below. SELECT In the above syntax, t1 is an alias of table_1 and t2 is of table_2. When the names of the key columns are not same in both the tables, we need to match them using the ON keyword as shown above. We’ll now discuss a few important joins in SQL. Inner JoinInner join merges two tables by columns and returns only the matching records (based on the specified columns) in both the tables. In the below query result, we can see that only the records with common id in both left_table and right_table are returned. SELECT
Or SELECT Inner Join (Image by author)Left JoinLeft join merges two tables by columns and returns all the records in the left table but only the matching records (based on the specified columns) from the right table. In the below query result, we can see the records with common id in both the tables along with all the records of the left_table. Records in the right_table with no matching idin the left_table have NULL. SELECT Or SELECT Left Join (Image by author)Right JoinRight join merges two tables by columns and returns all the records in the right table but only the matching records (based on the specified columns) from the left table. In the below query result, we can see the records with common id in both the tables along with all the records of the right_table. Records in the left_table with no matching idin the right_table have NULL. SELECT Or SELECT Right Join (Image by author)
Full JoinFull join can be considered as a combination of left and right joins. Full join merges two tables by columns and returns all the records in both the left and right tables. In the below query result, we can see that all the records of both the tables are returned. Records with no matching id in the other table have NULL. SELECT Or SELECT Full Join (Image by author)
Cross JoinCross join returns the cartesian product of two tables. Cartesian product of two sets A = {1, 2}, B = {3, 4} is A x B = {(1, 3), (1, 4), (2, 3), (2, 4)}. We need not specify a key column in cross joins. SELECT Cross Join (Image by author)Semi JoinSemi join is technically not an SQL join but works like a join. Semi join returns the matching records in the left table based on a key column in the right table. Semi join doesn’t include the columns of the right table in the query result. In the below example, we want to return the records from the left_tablewith matchingidin theright_table. In other words, we want the records in theleft_tablewhoseidis present in theright_table. SELECT Semi Join (Image by author)Anti JoinAnti join is also technically not an SQL join but works like a join. Anti join returns the non-matching records in the left table based on a key column in the right table. Anti join also doesn’t include the columns of the right table in the query result. In the below example, we want to return the records from the left_tablewhose id doesn’t match with the idoftheright_table. In other words, we want the records in theleft_tablewhoseidis not present in theright_table. SELECT Anti Join (Image by
author)Self JoinSelf join enables us to join a table with itself. In the below query, we need to find the records with the same left value. For this, we have joined the table with itself and filtered the records with same left value but different id. SELECT Self join (Image by author)Merging tables by rowsUnionUnion merges two tables by rows, provided the data types of the columns of one table matches with that of the other. We cannot merge a table having column data types as integer and text with a table having column data types as text and integer. However, we can merge two tables even if the column names of one table doesn’t match with that of the other. Union returns only the unique records of both the tables. ( Union
(Image by author)Union AllSimilar to Union, Union All also merges tables by rows. Unlike Union, Union All retains the duplicate records of both the tables. In the below query result, we have merged the id of left_table and right_table. We can see a few duplicates in the result. ( Union All (Image by author)IntersectIntersect returns the common records of both the tables. In the below query result, we can see the common ids of left_table and right_table. ( Intersect (Image by author)EXCEPTExcept returns the records from the first table (left table) which are not present in the second table (right table). In the below query result, we can see the ids of left_table which aren’t present in the right_table. Except (Image by author)Example QueriesWe’ll use the dvd_rental database downloaded from here and restore it. Below is the documentation to restore a database in PostgreSQL. 1. Top 5 frequent rentersIn this example, we need to find the top 5 customers who rented the most. For this, we’ll
SELECT Image by author2. Top & bottom 5 customers by revenue generatedIn this example, we’ll use common table expressions (CTE). With CTEs, we can create temporary table that exist for a particular query. Below is the official Postgres documentation on CTEs. In this example, we need to find out top and bottom 5 customers who generated the most revenue. For this, we’ll 1. Create a CTE named revenue_per_customer by
2. Select top 5 customers by revenue from the above CTE by
3. Select bottom 5 customers by revenue from the above CTE by
4. Merging the above two results using UNION. WITH revenue_per_customer ASImage by author We can also get the above query result using window functions. Below is the official Postgres documentation on window functions. To find out the top and bottom 5 customers who generated the most revenue using window functions, we’ll 1. Create a CTE named total_amt_rank by
2. Select top 5 customers by revenue by selecting the customers whose total_amount_rankis BETWEEN 1 and 5 from the above CTE. 3. Select bottom 5 customers by revenue from the above CTE by
4. Merging the above two results using UNION. WITH total_amt_rank AS Image by author3. Top 5 countries having the highest rentalsIn this example, we need to find the top 5 countries with the highest rentals. For this, we’ll
SELECT Image by authorThere are a few addresses and cities with no customers. Using inner join omits such records. In the below query, we’ll look at how the result will include addresses without customers on using left join. 4. City/address with no customers?There are a few cities and addresses without any customers (these may be store addresses). Using inner joins would have omitted them from the results as there are no matching entries in the other table. For example, a city named London in Canada has no matching city_id in the address table. Using inner join would have omitted London in Canada from the result. Similarly, four addresses in Canada and Australia have no matching address_id in the customer table. SELECT Image by author5. Countries with no customerIn this example, we’ll find the countries with no customers by 1. Creating a subquery to find the countries with at least one customer by
2. Selecting countryfromcountrytable where country_idis not present in the country_idof the above subquery. SELECT Image by author6. Are there any stores in Australia?In the above example, we saw that Australia has no customers. In this example, we’ll see are there any stores in Australia by
Left join ensures that countries with no cities and cities with no stores are also included in the query result. SELECT Image by authorThere is one store in Australia. In fact, there are just two stores in the whole database. We’ll view them using the below query. SELECT * FROM store; Image by author7. Languages with no filmsIn this example, we’ll see if there are any languages with no films by
SELECT Image by authorWe see a few languages with no films in the database. We’ll make sure that it’s not an error by selecting the films with language_id in (2,3,4,5,6) from the film table. The query result should return no records. SELECT Image by author8. Popularity of films by category in IndiaIn this example, we’ll find the number of rentals per film category in India by joining the required tables as discussed in the earlier examples and
SELECT Image by author9. Films with only a single actorIn this example, we‘ll find the films with a single actor by
SELECT Image
by author10. Number of films of an actor by categoryIn this example, we’ll find the number of films of an actor by film category by
WITHImage by author 11. Popular categories of an actorIn the above example, we found the number of films of an actor by film category. In this example, we’ll find the popular categories of an actor (i.e. the categories in which an actor has the most films) by
WITHImage by author This brings this article to an end. We’ve discussed ways of merging tables by rows or columns using SQL along with a few examples using the dvd_rental database. These are the fundamental concepts that are used in almost every query we write in SQL. We may not frequently use a few of them in practice, but knowing them is necessary. Can we join 2 tables without common column?There are few ways to combine the two tables without a common column including Cross Join (Cartesian Product) and UNION. This is not a join but can be useful for merging tables in SQL.
Can we join two tables on two columns SQL?The SQL JOIN is one of the basic tools for data analysts working with SQL. Relational databases are built in a way such that analytical reports usually require combining information from several tables. You'll be joining tables, sometimes by one column and other times by two or more columns.
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