Q61. Function to count results?
`COUNT()`. `COUNT(*)` counts rows. `COUNT(column)` counts non-NULL values. ```sql SELECT COUNT(*) FROM orders; -- Total orders SELECT COUNT(shipped_date) FROM orders; -- ...
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Q62. Which are aggregate functions?
**Aggregate functions** perform a computation on a set of values across multiple rows and return a single summarizing value: ### Core Standard Aggregate Functions: 1. **`...
Q63. Return number of records in Customers?
To return the total count of rows in the `Customers` table, use **`COUNT(*)`**: ```sql SELECT COUNT(*) AS total_customers FROM Customers; ``` ### `COUNT(*)` vs `COUNT(col...
Q64. Sorting direction keywords?
In the SQL `ORDER BY` clause, sorting direction is controlled by two keywords: 1. **`ASC` (Ascending)**: Sorts from lowest to highest (1 to 9, A to Z, oldest date to newe...
Q65. Default sort order if not specified?
If no direction keyword is specified in an `ORDER BY` clause, the default sort order is **`ASC` (Ascending)**: ```sql -- These two queries produce identical ordering: SEL...
Q66. Top 3 students by mark?
```sql -- MySQL / PostgreSQL SELECT name, mark FROM Students ORDER BY mark DESC LIMIT 3; -- SQL Server SELECT TOP 3 name, mark FROM Students ORDER BY mark DESC; -- Oracle...
Q67. Sort Customers descending by FirstName?
To sort the `Customers` table in descending alphabetical order (Z to A) by `FirstName`, append `ORDER BY FirstName DESC`: ```sql SELECT * FROM Customers ORDER BY FirstNam...
Q68. Correct GROUP BY syntax?
```sql SELECT name, COUNT(name) FROM customers GROUP BY name; ``` In standard SQL (and MySQL 5.7+ with `ONLY_FULL_GROUP_BY`), any non-aggregated column in SELECT must app...
Q69. WHERE vs HAVING?
| WHERE | HAVING | |-------|--------| | Filters **rows** | Filters **groups** | | Executes **before** GROUP BY | Executes **after** GROUP BY | | Cannot use aggregates | C...
Q70. What is JOIN used for?
A **`JOIN`** clause in SQL combines rows from two or more tables based on a related column between them (typically a Foreign Key referencing a Primary Key). ### The Need ...