What Can SQL do? SQL DML and DDL. What is SQL? 1. SQL stands for Structured Query Language. 2. SQL lets you access and manipulate databases

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1 What is? 1. stands for Structured Query Language 2. lets you access and manipulate databases 3. is an ANSI (American National Standards Institute) standard Note: is not case sensitive. SELECT is the same as select. What Can do? can retrieve data from a database/table 2. can insert records in a database/table 3. can update records in a database/table 4. can delete records from a database/table 5. can create new databases/table 6. can create new tables in a database/table DML and DDL can be divided into two parts:the Data Manipulation Language (DML) and the Data Definition Language (DDL). DML Commands: 1. SELECT - extracts data from a table 1 / 33

2 2. UPDATE - updates data in a table 3. DELETE - deletes data from a table 4.INSERT INTO- inserts new data into a table DDL Commands: CREATE DATABASE- creates a new database 2.CREATE TABLE- creates a new table 3.ALTER TABLE- modifies a table 4.DROP TABLE- delete a table 5.CREATE INDEX- creates an index 6. DROP INDEX- deletes an index Data Types Data type Description Max Size: VARCHAR2( size ) 2 / 33

3 Variable length character string having maximum length You must specify size size bytes minimum is 1 CHAR( size ) Fixed length character data of length size bytes Integer/INT Integer Number. DECIMAL( p,s ) 3 / 33

4 Number having precision p Magnitude 1E E125 DATETIME A date and time combination in YYYY-MM-DD HH:MM:SS format DATE A date in YYYY-MM-DD format The CREATE DATABASE Command The CREATE DATABASE statement is used to create a Database. 4 / 33

5 CREATE DATABASE Syntax CREATE DATABASE database_name CREATE DATABASE Example CREATE DATABASE KVPALAMPUR ; This command will create a Database with the name KVPALAMPUR The CREATE TABLE Command The CREATE TABLE statement is used to create a table in a database. CREATE TABLE Syntax CREATE TABLE table_name ( column_name1 data_type, column_name2 data_type,... ) The data type specifies what type of data the column can hold. CREATE TABLE Example Now we want to create a table called "Student" that contains four columns: Roll_No, Name, 5 / 33

6 Class, City. We use the following CREATE TABLE statement: CREATE TABLE Student ( Roll_No integer, Name varchar(30), Class varchar(5), City varchar(30) ) The Roll_No column is of type integer and will hold a number. The Name, Class and City columns are of type varchar and will hold character data. The empty "Student" table will now look like this: 6 / 33

7 The DROP TABLE Command The DROP TABLE statement is used to delete a table. Syntax: DROP TABLE table_name Example: Suppose if we want to drop table student, we can use DROP TABLE command like this Drop Table Student ; Note: Before using Drop Command make sure that table has no records exist. Drop command will not work on a table if it has has some records. The ALTER TABLE Command The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. 7 / 33

8 ALTER TABLE Syntax To add a column in a table, use the following syntax: ALTER TABLE table_name ADD column_name data-type To delete a column in a table, use the following syntax ALTER TABLE table_name DROP COLUMN column_name To change the data type of a column in a table, use the following syntax: ALTER TABLE table_name MODIFY column_name data-type ALTER TABLE Example Look at the "Student" table: Now we want to add a column named "DateOfBirth" in the "Student" table. 8 / 33

9 We use the following statement: ALTER TABLE Student ADD DateOfBirth date The "Student" table will now like this: Change Data Type Example Now we want to change the data type of the column named "Class" in the "Student" table. We use the following statement: ALTER TABLE Student ALTER COLUMN Class integer Notice that the "Class" column is now of type integer. 9 / 33

10 DROP COLUMN Example Next, we want to delete the column named "DateOfBirth" in the "Student" table. We use the following statement: ALTER TABLE Student DROP COLUMN DateOfBirth The "Student" table will now like this: DML Commands: Quotes Around Text Fields uses single quotes around text values (most database systems will also accept double quotes). 10 / 33

11 However, numeric values should not be enclosed in quotes. For text values: This is correct: SELECT * FROM Student WHERE Name='Abhey' This is wrong: SELECT * FROM Student WHERE Name=Abhey For numeric values: This is correct: SELECT * FROM Student WHERE Roll_No=2 This is wrong: SELECT * FROM Student WHERE Roll_No='2' The INSERT INTO Command 11 / 33

12 The INSERT INTO Command is used to insert a new record in a table. INSERT INTO Syntax We can write INSERT INTO command in two forms. The first form doesn't specify the column names where the data will be inserted, only their values: INSERT INTO table_name VALUES (value1, value2, value3,...) The second form specifies both the column names and the values to be inserted: INSERT INTO table_name (column1, column2, column3,...) VALUES (value1, value2, value3,...) INSERT INTO Example We have the following "Student" table: 12 / 33

13 Now we want to insert some records in the "Student" table. We use the following statement: INSERT INTO Student VALUES (1,'Amisha', 'XII', 'Palampur') INSERT INTO Student VALUES (2,'Usha', 'XII', 'Holta') INSERT INTO Student VALUES (3,'Sneh', 'XII', 'Palampur) INSERT INTO Student VALUES (4,'Nishant', 'XI', 'Baijnath') INSERT INTO Student VALUES (5,'Gaurav', 'XI', 'Paprola') The "Student" table will now look like this: Insert Data Only in Specified Columns 13 / 33

14 It is also possible to only add data in specific columns. The following statement will add a new row, but only add data in the "Roll_No", "Name" and the "Class" columns: INSERT INTO Student (Roll_No, Name, Class) VALUES (6, 'Abhay', 'XI') The "Student" table will now look like this: The UPDATE Statement The UPDATE statement is used to update existing records in a table. UPDATE Syntax UPDATE table_name SET column1=value, column2=value2,... WHERE 14 / 33

15 some_column=some_value Note: If you omit the WHERE clause, all records will be updated! UPDATE Example The "Student" table: Now we update the record of student "Abhey" in the "Student" table. We use the following command: UPDATE Student SET City='Sagoor' WHERE Name='Abhey' The "Student" table will now look like this: 15 / 33

16 The DELETE Statement The DELETE statement is used to delete rows in a table. DELETE Syntax DELETE FROM table_name WHERE some_column=some_value Note: If we omit the WHERE clause, all records will be deleted.be very careful when deleting records. You cannot undo this command! The SELECT Statement The SELECT statement is used to select data from a database. SELECT Syntax SELECT column_name(s) FROM table_name 16 / 33

17 and SELECT * FROM table_name SELECT Example The "Student" table: Now we select all the records from the table above. We use the following SELECT statement: SELECT * from Student ; 17 / 33

18 The use of asterisk (*) is an easy way to list all the records from a table. The result of this command will look like this: Now we select the contents of the columns named "Name" and "Class" from Student table. We use the following SELECT statement: SELECT Name,Class FROM Student ; The result will look like this: 18 / 33

19 The SELECT DISTINCT Statement In a table, some of the columns may contain duplicate values. Sometimes we want to list only the different (distinct) values from a table. The DISTINCT keyword can be used to return only distinct (different) values. SELECT DISTINCT Syntax SELECT DISTINCT column_name(s)from table_name The "Student" table: 19 / 33

20 Now above. we the want to select only thestatement: distinct values from the column named "City" from the table We following SELECT SELECT DISTINCT City FROM Persons The use result will look like this: Clause is used to extract only those records that fulfill a specified criterion. The WHERE clause WHERE Syntax SELECT column_name(s)from table_name WHERE column_name operator value WHERE Clause Example The "Student" table: 20 / 33

21 Nowuse we the want to select onlywhere thestatement: students living in the ;city "Palampur" from the table above. We following SELECT SELECT * FROM Student City='Palampur' Operators Allowed in the WHERE Clause With the WHERE clause, the following operators can be used: Operator Description = Equal 21 / 33

22 <> Not equal > Greater than < Less than >= Greater than or equal <= Less than or equal 22 / 33

23 BETWEEN Between an inclusive range LIKE Search for a pattern IN To specify multiple possible values for a column The AND & OR Operators The AND operator displays a record if both the first condition and the second condition is true. The OR operator displays a record if either the first condition or the second condition is true. AND Operator Example The "Student" table: 23 / 33

24 Now "Palampur": we the want to select only thestatement: students with the name equal to "Sneh" AND the City equal to We following SELECT * will FROM Student Name='Sneh' AND City='Palampur' The use result look likeselect this:where OR Operator Example Now we want to select only those students with the name equal to "Nishant" OR City equal to "Sagoor": We use the following SELECT statement: SELECT * FROM Student WHERE Name='Nishant' OR City='Sagoor' The result will look like this: 24 / 33

25 The ORDER BY Keyword The ORDER BY keyword is used to sort the result by a specified column. The ORDER BY keyword sort the records in ascending order by default. If we want to sort the records in a descending order, we can use the DESC keyword. ORDER BY Syntax SELECT column_name(s) FROM table_name ORDER BY column_name(s) ASC DESC ORDER BY Example The "Student" table: 25 / 33

26 Now we select all records from the table above, however, we want to sort the students by their name. We use the following SELECT statement: SELECT * FROM Student ORDER BY Name The result will look like this: The GROUP BY Statement The GROUP BY statement is used in conjunction with the aggregate functions to group the result-set by one or more columns. GROUP BY Syntax SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name 26 / 33

27 GROUP BY Example We have the following "Order" table: Now we want to find the total sum of each Customer. We will have to use the GROUP BY clause to group the items. We use the following statement: SELECT Cname,SUM(Price) FROM Order GROUP BY Customer The result will look like this: 27 / 33

28 The HAVING Clause The HAVING clause was added to because the WHERE keyword could not be used with aggregate functions. HAVING Syntax SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value HAVING Example We have the following "Order" table: 28 / 33

29 Now we the want to findlike if any of the customers have a total order of HAVING greater than We use following SELECT CName,SUM(Price) FROM Order GROUP BY CName SUM(Price)>25000 The result will look this:statement: Nowadd we an want to findlike if the "Ayan" or "Abhay" have a total OR order of more than We ordinary WHERE clause to the statement: SELECT GROUP BY CName,SUM(Price) CName HAVING FROM SUM(Price)>30000 Order WHERE CName='Ayan' CName='Abhay' The result will look this:customers The IN Operator The IN operator allows you to specify multiple values in a WHERE clause. IN Syntax SELECT coumn_name(s)from table_name WHERE column_name IN (value1,value2,...) IN Operator Example The "Order" table: 29 / 33

30 Now we want to select all the records with IName equal to "TV" or "AC" from the table above. We use the following SELECT statement: SELECT * FROM Order WHERE IName IN ('TV','AC') The result will look like this: 30 / 33

31 The BETWEEN Operator The BETWEEN operator selects a range of data between two values. The values can be numbers, text, or dates. BETWEEN Syntax SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2 BETWEEN Operator Example The "Order" table: Now we want to select the orders with Price between and from the table above. We use the following SELECT statement: 31 / 33

32 SELECT * FROM Order WHERE Price BETWEEN AND The result will look like this: Date Data Types My comes with the following data types for storing a date or a date/time value in the database: - DATE - format YYYY-MM-DD DATETIME - format: YYYY-MM-DD HH:MM:SS TIMESTAMP - format: YYYY-MM-DD HH:MM:SS YEAR - format YYYY or YY Note: The date types are chosen for a column when you create a new table in your database! Working with Dates The "Order" table: 32 / 33

33 Now we want to select the records with an OrderDate of " " from the table above. We use the following SELECT statement: SELECT * FROM Order WHERE OrderDate=' ' The result will look like this: 33 / 33