The JOIN operator is used to merge related data from different tables and associate rows in the tables by specifying join conditions. Common JOIN types include INNER JOIN (returns matching rows), LEFT JOIN (returns all left table rows), RIGHT JOIN (returns all right table rows), and FULL JOIN (returns all table rows). JOIN queries should be capitalized and specify the join columns. Performance is an important factor to consider when writing JOIN queries.
Usage of JOIN in SQL
JOIN is used in SQL to combine related data from different tables operator. It allows you to extract data from multiple tables and relate them based on their common columns.
Syntax
<code>SELECT column_list FROM table1 JOIN table2 ON join_condition;</code>
Where:
column_list
is the column to be retrieved from the joined table. table1
and table2
are the tables to be joined. join_condition
Specifies the condition used to join rows in the table. Common JOIN types
table1
, and a subset of matching rows in table2
. table2
, and a subset of matching rows in table1
. Usage Example
For example, the following query uses INNER JOIN to get from the customers
table and the orders
table Customer's Orders:
<code>SELECT * FROM customers INNER JOIN orders ON customers.customer_id = orders.customer_id;</code>
This query will return a table with the following columns:
customer_id
customer_id column will be in the two tables rows are associated. INNER JOIN ensures that only orders from customers that appear in both tables are returned.
Note
.
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