SQL Questions

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties.

Properties of Sub-Query

- A sub-query must be enclosed in the parenthesis.

- A sub-query must be put in the right hand of the comparison operator, and

- A sub-query cannot contain an ORDER-BY clause.

- A query can contain more than one sub-query.

Types of Sub-Query

- Single-row sub-query, where the sub-query returns only one row.

- Multiple-row sub-query, where the sub-query returns multiple rows,. and

- Multiple column sub-query, where the sub-query returns multiple columns

Use the DBMS_OUTPUT package. Another possible method is to use the SHOW ERROR command.

SELECT "column_name"

FROM "table_name"

WHERE "column_name" IS NULL.

SQL keyword ORDER BY is used to sort the result-set.

SQL JOIN allows access to records of other table based on the given conditions between two tables.

Ex: If we are provided with the department ID of each employee, then we can use the department ID of the employee table to merge with the department ID of the department table to access department names.

UNION operation allows addition of 2 similar data sets to create a resulting set that contains all the data from the source data sets.

Ex: If we are provided with 2 employee tables of the same structure, we can UNION them to create a singular result that will contain all employee from both the table.

Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db and can be used this as the Disaster Recovery plan. The key feature of log shipping is that it will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.

There are many ways to find second highest salary of Employee in SQL, you can either use SQL Join or Subquery to solve this problem. Here is SQL query using Subquery :

SELECT MAX(Salary) from Employee WHERE Salary NOT IN (select MAX(Salary) FROM Employee );