JOIN
JOIN is used to combine rows from two or more tables based on a related column between them. It allows you to extract data from multiple tables and present it as a single result set.
There are several types of JOIN clauses:
- INNER JOIN: Returns only the rows that have matching values in both tables.
- LEFT JOIN: Returns all the rows from the left table and the matching rows from the right table.
- RIGHT JOIN: Returns all the rows from the right table and the matching rows from the left table.
- FULL OUTER JOIN: Returns all the rows from both tables.
Examples
Here are some examples of using JOIN clauses:
sql
-- Select all rows from the system_metrics table and idc_info table where the idc_id matches
SELECT a.*
FROM system_metrics a
JOIN idc_info b
ON a.idc = b.idc_id;
-- Select all rows from the idc_info table and system_metrics table where the idc_id matches, and include null values for idc_info without any matching system_metrics
SELECT a.*
FROM idc_info a
LEFT JOIN system_metrics b
ON a.idc_id = b.idc;
-- Select all rows from the system_metrics table and idc_info table where the idc_id matches, and include null values for idc_info without any matching system_metrics
SELECT b.*
FROM system_metrics a
RIGHT JOIN idc_info b
ON a.idc = b.idc_id;-- Select all rows from the system_metrics table and idc_info table where the idc_id matches
SELECT a.*
FROM system_metrics a
JOIN idc_info b
ON a.idc = b.idc_id;
-- Select all rows from the idc_info table and system_metrics table where the idc_id matches, and include null values for idc_info without any matching system_metrics
SELECT a.*
FROM idc_info a
LEFT JOIN system_metrics b
ON a.idc_id = b.idc;
-- Select all rows from the system_metrics table and idc_info table where the idc_id matches, and include null values for idc_info without any matching system_metrics
SELECT b.*
FROM system_metrics a
RIGHT JOIN idc_info b
ON a.idc = b.idc_id;