Structured Query Language (SQL).pptx
- 1. 1 Structured Query Language (SQL) What is SQL? Is a language of database, it includes database creation, deletion, fetching rows and modifying rows etc. SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in relational database.
- 2. 2 Why SQL? • Allows users to access data in relational database management systems. • Allows users to describe the data. • Allows users to define the data in database and manipulate that data. • 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
- 3. 3 SQL Syntax • SQL is followed by unique set of rules and guidelines called Syntax. This tutorial gives you a quick start with SQL by listing all the basic SQL Syntax: • All the SQL statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon (;).
- 4. 4 SQL Syntax • Important point to be noted is that SQL is case insensitive, which means SELECT and select have same meaning in SQL statements, but MySQL makes difference in table names. So if you are working with MySQL, then you need to give table names as they exist in the database.
- 5. 5 SQL Statements Most of the actions you need to perform on a database are done with SQL statements. Semicolon after SQL Statements? Some database systems require a semicolon at the end of each SQL statement. Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.
- 6. 6 SQL DML and DDL SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language (DDL).
- 7. 7 DDL - Data Definition Language: The DDL part of SQL permits database tables to be created or deleted. It also defines indexes (keys), specifies links between tables, and imposes constraints between tables. The most important DDL statements in SQL are: CREATE DATABASE - creates a new database ALTER DATABASE - modifies a database CREATE TABLE - creates a new table
- 8. 8 DDL - Data Definition Language: ALTER TABLE - modifies a table DROP TABLE - deletes a table CREATE INDEX - creates an index (search key) DROP INDEX - deletes an index
- 9. 9 DML - Data Manipulation Language: The query and update commands form the DML part of SQL: SELECT - extracts data from a database UPDATE - updates data in a database DELETE - deletes data from a database INSERT INTO - inserts new data into a database
- 10. 10 1. SQL SELECT Statement The SELECT statement is used to select data from a database. The result is stored in a result table, called the result-set. SQL SELECT Syntax: SELECT column_name(s) FROM table_name And SELECT * FROM table_name Note: SQL is not case sensitive. SELECT is the same as select.
- 11. 11 Example: SELECT Table Name: Students StudentsID LastName FirstName Address City 1 Cabuso Fernan San Pedro Puerto Princesa 2 Porras Ellen Grace Alfonso XIII Quezon 3 Dela Cruz Steven Tabon Quezon Now we want to select the content of the columns named "LastName" and "FirstName" from the table above. We use the following SELECT statement: SELECT LastName, FirstName FROM Students
- 12. 12 Example: SELECT Table Name: Students The result-set will look like this: LastName FirstName Cabuso Fernan Porras Ellen Grace Dela Cruz Steven
- 13. 13 Example: SELECT Table Name: Students Now we want to select all the columns from the “Students" table. We use the following SELECT statement: SELECT * FROM Students Or SELECT * FROM Students Tip: The asterisk (*) is a quick way of selecting all columns!
- 14. 14 Example: SELECT Table Name: Students The result-set will look like this: StudentsID LastName FirstName Address City 1 Cabuso Fernan San Pedro Puerto Princesa 2 Porras Ellen Grace Alfonso XIII Quezon 3 Dela Cruz Steven Tabon Quezon
- 15. 15 2. SQL SELECT DISTINCT Statement In a table, some of the columns may contain duplicate values. This is not a problem, however, sometimes you will want to list only the different (distinct) values in a table. The DISTINCT keyword can be used to return only distinct (different) values. SQL SELECT DISTINCT Syntax: SELECT DISTINCT column_name(s) FROM table_name
- 16. 16 Example: SELECT DISTINCT Table Name: Students Now we want to select only the distinct values from the column named "City" from the table above. StudentsID LastName FirstName Address City 1 Cabuso Fernan San Pedro Puerto Princesa 2 Porras Ellen Grace Alfonso XIII Quezon 3 Dela Cruz Steven Tabon Quezon
- 17. 17 Example: SELECT DISTINCT Table Name: Students We use the following SELECT statement: SELECT DISTINCT City FROM Students The result-set will look like this: City Puerto Princesa Quezon
- 18. Thank you