Database/SQL Flashcards
What is a DataBase?
A database is a collection of information that is organized so that it can be easily accessed, managed and updated.
What is a Relational Database?
A relational database is a type of database. It uses a structure that allows us to identify and access data in relation to another piece of data in the database. Often, data in a relational database is organized into tables. Tables can have hundreds, thousands, sometimes even millions of rows of data. These rows are often called records.
Tables can also have many columns of data. Columns are labeled with a descriptive name (say, age for example) and have a specific data type
What is a RDBMS?
A relational database management system (RDBMS) is a program that allows you to create, update, and administer a relational database. Most relational database management systems use the SQL language to access the database.
What is SQL?
SQL (Structured Query Language) is a programming language used to communicate with data stored in a relational database management system. SQL syntax is similar to the English language, which makes it relatively easy to write, read, and interpret.
Many RDBMSs use SQL (and variations of SQL) to access the data in tables. For example, SQLite is a relational database management system. SQLite contains a minimal set of SQL commands (which are the same across all RDBMSs). Other RDBMSs may use other variants.
Why do we need SQL?
Allows users to access data in the relational database management systems.
Allows users to describe the data.
Allows users to define the data in a database and manipulate that data.
Allows to embed within other languages using SQL modules, libraries & pre-compilers.
Allows users to create and drop databases and tables.
Allows users to create view, stored procedure, functions in a database.
Allows users to set permissions on tables, procedures and views.
What is a Primary Key?
A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values.
A table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key.
If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).
What is a Foreign Key?
A foreign key is a key used to link two tables together. This is sometimes also called as a referencing key.
A Foreign Key is a column or a combination of columns whose values match a Primary Key in a different table.
The relationship between 2 tables matches the Primary Key in one of the tables with a Foreign Key in the second table.
What are some SQL statements?
DDL - Data Definition Language - CREATE, ALTER, DROP
DML - Data Manipulation Language - SELECT, INSERT, UPDATE, DELETE
DCL - Data Control Language - GRANT, REVOKE
TCL - Transaction Control Language - SAVEPOINT, ROLLBACK, COMMIT
What is SQL Where?
The SQL WHERE clause is used to specify a condition while fetching the data from a single table or by joining with multiple tables. If the given condition is satisfied, then only it returns a specific value from the table. You should use the WHERE clause to filter the records and fetching only the necessary records.
The WHERE clause is not only used in the SELECT statement, but it is also used in the UPDATE, DELETE statement.
What is Insert Query?
The SQL INSERT INTO Statement is used to add new rows of data to a table in the database.
INSERT INTO TABLE_NAME (column1, column2, column3,…columnN) VALUES (value1, value2, value3,…valueN);
What is SQL Join?
The SQL Joins clause is used to combine records from two or more tables in a database. A JOIN is a means for combining fields from two tables by using values common to each.
INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL JOIN
