Joints and Aggregation

Sources

1. SQL Joints (Lecture Slides)
2. SQL Aggregation (Lecture Slides)

Joints

Joins combine rows from different tables through related columns. They allow for the retrieval and presentation of related data.

NOTE

Types of Joints

1. Inner Join: Only returns rows with matching values.
2. Left (Outer) Join: Returns all rows from the left table and the matching rows from the right table. If no matches, NULL in the right table.
3. Right (Outer) Join: Returns all rows from the right table and the matching rows from the left table. If no matches, NULL in the left table.
4. Full (Outer) Join: Returns all rows from both table. Returns NULL in either when one is not matching with any.
5. Cross Join: Returns the combinations of all rows in both tables.

Aggregation

Aggregate functions perform calculations on a set of values and generates a result.

NOTE

Types of Aggregation

1. COUNT(): Counts the number of rows.
2. SUM(): Provides the sum of a numeric column.
3. AVG(): Provides the average of a numeric column.
4. MIN(): Finds the minimum in a column.
5. MAX(): Finds the maximum in a column.
6. GROUP BY(): Groups rows with the same values in a specified column.