In this video of code decode we have covered most asked SQL Interview Questions and answers for java developer with examples for both freshers and experienced.
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SQL interview question and answer part 2 : • SQL Interview Question...
Databases can be found in almost all software applications. SQL is the standard language to query a database. Thus most asked sql interview questions is a must go through before any java interview questions faced in real time
We live in a data-driven world: people search through data to find insights to inform strategy, marketing, operations, and a plethora of other categories. There are a ton of businesses that use large, relational databases, which makes a basic understanding of SQL a great employable skill not only for data scientists, but for almost everyone.
Structured Query Language or SQL is a standard Database language which is used to create, maintain and retrieve the data from relational databases like MySQL, Oracle, SQL Server, PostGres, etc
As the name suggests, it is used when we have structured data (in the form of tables). All databases that are not relational (or do not use fixed structure tables to store data) and therefore do not use SQL, are called NoSQL databases. Examples of NoSQL are MongoDB, DynamoDB, Cassandra, etc
How to find third height Salary is very frequently and most asked sql interview questions
What are Indexes and How to create an index in SQL? you will always face this as most asked sql interview questions
Indexes are database objects which help in retrieving records quickly and more efficiently. Column indexes can be created on both Tables and Views. By declaring a Column as an index within a table/ view, the user can access those records quickly by executing the index. Indexes with more than one column are called Clustered indexes.
Syntax:CREATE INDEX INDEX_NAME ON TABLE_NAME(COL1, COL2);
The syntax to drop an Index is DROP INDEX INDEX_NAME on TABLE_NAME;
Indexes are known to improve the efficiency of SQL Select queries
Suppose we need to search by employee name = Manoj
What goes on behind the scenes is Every single row is checked to see if the employee_name matches with Manoj. This effectively means that the entire table will have to be scanned (known as the full table scan).
An index is a data structure that stores the values for a certain specific column of a table and helps us avoid a full table scan.
Database Indexing in reality, allows us to cut down the number of rows/records that need to be examined when a select query with a where clause is executed.
Few DS are :
B-tree - Database indexes will also store pointers which are simply reference information for the location of the additional information in memory. Basically the index holds the company_id and that particular row’s home address on the memory disk.
The query looks for the specific row in the index; the index refers to the pointer which will find the rest of the information.
Index takes up additional space, so the larger the table, the bigger the index.
Every time you perform an add, delete, or update operation, the same operation will need to be performed on the index as well.
If we drop a table, does it also drop related objects like constraints, indexes, columns, default, views and stored procedures?
Yes, SQL server drops all related objects, which exists inside a table like constraints, indexex, columns, defaults etc.
But dropping a table will not drop views and sorted procedures as they exist outside the table.
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4 июл 2024
