SQL

What is a Join in SQL?

A SQL join clause combines records from two or more tables in a relational database. It creates a set that can be saved as a table or used as it is. A JOIN is a means for combining fields from two tables (or more) by using values common to each.

TABLE

A Table in RDBMS refers to data arranged in rows and columns, which defines a database entity.

column

Database tables are made of different columns (fields) corresponding to the attributes of the object described by the table.

WHAT IS STRUCTURED DATA AND UNSTRUCTURED DATA

For the most part, structured data refers to information with a high degree of organization, such that inclusion in a relational database is seamless and readily searchable by simple, straightforward search engine algorithms or other search operations; whereas unstructured data is essentially the opposite

What is inner join and outer join?

Inner join. A join is combining the rows from two tables. An inner join attempts to match up the two tables based on the criteria you specify in the query, and only returns the rows that match. If a row from the first table in the join matches two rows in the second table, then two rows will be returned in the results.

FROM

Lists the tables that contain the fields listed in the SELECT clause.

What is the difference between SQL and PL/SQL?

PL/SQL is a dialect of SQL that adds procedural features of programming languages in SQL. It was developed by Oracle Corporation in the early 90's to enhance the capabilities of SQL.

Query

Queries are the main way to make a request for information from a database. Queries consist of questions presented to the database in a predefined format, in most cases SQL (Structured Query Language) format.

What is the difference between SQL and MySQL or SQL Server?

SQL or Structured Query Language is a language; language that communicates with a relational database thus providing ways of manipulating and creating databases. MySQL and Microsoft's SQL Server both are relational database management systems that use SQL as their standard relational database language.

COMMIT

The COMMIT command in SQL marks the finalization of a database transaction.

INSERT

The INSERT is a SQL command used to add a new record to a table within a database.

JOIN

The JOIN is a SQL command used to retrieve data from 2 or more database tables with existing relationship based upon a common attribute.

NULL

The NULL SQL keyword is used to represent a missing value.

ROLLBACK

The ROLLBACK is a SQL command which cancels/undoes the proposed changes in a pending database transaction and marks the end of the transaction.

SELECT

The SELECT is a SQL command, which is the primary means for retrieving data from a RDBMS.

ROW(see record)

The record is a complete set of information presented within a RDBMS. Records are composed of different fields (columns) in a table and each record is represented with a separate row in this table.

What is the difference between a "where" clause and a "having" clause?

Where" is a kind of restiriction statement. You use where clause to restrict all the data from DB.Where clause is using before result retrieving. But Having clause is using after retrieving the data.Having clause is a kind of filtering command.

*

in SQL language, a star refers to all fields in a table.

Index

structure provided by an RDBMS in order to improve and optimize data processing. This is not a traditional relational database logical structure, it only comes with a few programs such as Access.

ORDER BY

when querying data with a SELECT statement, we can use this statement to organize by a certain category i.e. ORDER BY title; to return us the results listed in alphabetical order. Include keywords ASC (asciending) and DESC (descending) after the column name to specify how you want them alphabetized.

JOIN (INNER JOIN)

when you need information from two or more tables, you can combine them into a single table using JOIN.