Basic RDBMS-Day3
SQL
DDL statements
DML statements
Aggregate functions
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SQL
SQL is used to make a request to retrieve data from a Database.
The DBMS processes the SQL request, retrieves the requested data from the
Database, and returns it.
This process of requesting data from a Database and receiving back the
results is called a Database Query and hence the name Structured Query
Language.
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SQL
SQL is a language that all commercial RDBMS implementations understand.
SQL is a non-procedural language
We would be discussing SQL with respect to oracle syntax
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You cant write programs like the ones you would have done using C language
You can only write questions in English like language called queries which will fetch some data rows
from the database.
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Structured Query Language (SQL)
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Structured Query Language (SQL)
1979 Oracle Corporation introduces the first commercial RDBMS
1982 ANSI (American National Standards Institute) forms SQL Standards Committee
1983 IBM (International Business Machine) announces DB2 (a Database)
1986 ANSI (American National Standards Institute) SQL1 standard is approved
1987 ISO (International Organization for Standardization) SQL1 standard is approved
1992 ANSI (American National Standards Institute) SQL2 standard is approved
2000 Microsoft Corporation introduces SQL Server 2000, aimed at enterprise
applications
2004 SQL: 2003 standard is published
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Statements
DDL (Data Definition Language)
DML (Data Manipulation Language)
Create
Alter
Drop
Truncate
Insert
Update
Delete
Select
DCL (Data Control Language)
Grant
Revoke
Commit
Rollback
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SQL has three flavours of statements. The DDL, DML and DCL.
DDL is Data Definition Language statements. Some examples:
CREATE - to create objects in the database
ALTER - alters the structure of the database
DROP - delete objects from the database
TRUNCATE - remove all records from a table, including all spaces allocated for the records are
removed
COMMENT - add comments to the data dictionary
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command
DML is Data Manipulation Language statements. Some examples:
SELECT - retrieve data from the a database
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes all records from a table, the space for the records remain
CALL - call a PL/SQL or Java subprogram
EXPLAIN PLAN - explain access path to data
LOCK TABLE - control concurrency
DCL is Data Control Language statements. Some examples:
COMMIT - save work done
SAVEPOINT - identify a point in a transaction to which you can later roll back
ROLLBACK - restore database to original since the last COMMIT
SET TRANSACTION - Change transaction options like what rollback segment to use
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Data types
Number
Char
Varchar2
Long
date
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SQL supports various data types
Integers
Decimal numbers--- NUMBER, INTEGER .
Number is an oracle data type. Integer is an ANSI data type. Integer is equivalent of NUMBER(38)
The syntax for NUMBER is NUMBER(P,S) p is the precision and s is the scale. P can range from 1
to 38 and s from -84 to 127
Floating point numbers---- FLOAT
Fixed length character strings---- CHAR (len)
Fixed length character data of length len bytes. This should be used for fixed length data.
Variable length character strings --- Varchar2(len)
Variable length character string having maximum length len bytes. We must specify the size
Dates-----DATE
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NULL
Missing/unknown/inapplicable data represented as a null value
NULL is not a data value. It is just an indicator that the value is unknown
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Operators
Arithmetic operators like +, -, *, /
Logical operators: AND, OR, NOT
Relational operators: =, <=, >=, < >, < , >
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The Arithmetic operators are used to calculate something like given in the example below:
Select * from employee where sal * 1.1 > 1000 ;
The logical operators are used to combine conditions like:
Select * from employee where (sal > 1000 AND age > 25);
The above two examples also illustrate use of relational operators
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SQL-Data Definition Language
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Types Of Constraints
Column Level
Table
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Types Of Constraints
Primary Key Constraint
Foreign Key Constraint
Unique Constraint
Check Constraint
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SQL - CREATE TABLE
Syntax:
CREATE TABLE tablename
(
column_name
data_ type
constraints,
)
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Used to create a table by defining its structure, the data type and name of the various columns, the
relationships with columns of other tables etc.
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Create Table (Contd)
Implementing NOT NULL and Primary Key
EXAMPLE :
CREATE TABLE Customer_Details(
Cust_ID
Number(5)
Cust_Last_Name
VarChar2(20)
Cust_Mid_Name
VarChar2(4),
Cust_First_Name
VarChar2(20),
Account_No
Number(5)
Account_Type
VarChar2(10)
Bank_Branch
VarChar2(25)
Cust_Email
VarChar2(30)
);
CONSTRAINT Nnull1 NOT NULL,
CONSTRAINT Nnull2 NOT NULL,
CONSTRAINT Pkey1 PRIMARY KEY,
CONSTRAINT Nnull3 NOT NULL,
CONSTRAINT Nnull4 NOT NULL,
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Create Table (Contd)
Implementing Composite Primary Key
EXAMPLE :
CREATE TABLE Customer_Details(
CONSTRAINT Nnull7 NOT NULL,
Cust_ID
Number(5)
Cust_Last_Name
VarChar2(20)
CONSTRAINT Nnull8 NOT NULL,
Cust_Mid_Name
VarChar2(4),
Cust_First_Name
VarChar2(20),
Account_No
Number(5)
CONSTRAINT Nnull9 NOT NULL,
CONSTRAINT Nnull10 NOT NULL,
Account_Type
VarChar2(10)
Bank_Branch
VarChar2(25)
CONSTRAINT Nnull11 NOT NULL,
Cust_Email
VarChar2(30),
CONSTRAINT PKey3 PRIMARY KEY(Cust_ID,Account_No)
);
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Create Table (Contd)
Implementation of Unique Constraint
Create Table UnqTable(
ECode Number(6) Constraint PK11 Primary Key,
EName Varchar2(25) Constraint NNull18 NOT NULL,
EEmail Varchar2(25) Constraint Unq1 Unique
);
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Create Table (Contd)
Implementation of Primary Key and Foreign Key Constraints
CREATE TABLE EMPLOYEE_MANAGER(
Employee_ID
Number(6) CONSTRAINT Pkey2 PRIMARY KEY,
Employee_Last_Name
VarChar2(25),
Employee_Mid_Name
VarChar2(5),
Employee_First_Name
VarChar2(25),
Employee_Email
VarChar2(35),
Department
VarChar2(10),
Grade
Number(2),
MANAGER_ID
Number(6) CONSTRAINT Fkey2
REFERENCES EMPLOYEE_MANAGER(Employee_ID)
);
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Create Table (Contd)
Implementation of Check Constraint
EXAMPLE :
CREATE TABLE EMPLOYEE(
EmpNo NUMBER(5) CONSTRAINT PKey4 Primary Key,
EmpName Varchar(25) NOT NULL,
EmpSalary Number(7) Constraint chk Check (EmpSalary > 0 and EmpSalary <
1000000)
)
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Create Table (Contd)
Implementation of Default
CREATE TABLE TABDEF(
Ecode Number(4) Not Null,
Ename Varchar2(25) Not Null,
ECity char(10) DEFAULT Mysore
)
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SQL - ALTER TABLE
Add/Drop Column
Syntax:
ALTER TABLE tablename (ADD/MODIFY/DROP column_name)
ALTER TABLE Customer_Details
ADD Contact_Phone Char(10);
ALTER TABLE Customer_Details
MODIFY Contact_Phone Char(12);
ALTER TABLE Customer_Details
DROP (Contact_Phone);
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Used to modify the structure of a table by adding and removing columns
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SQL - ALTER TABLE
Add/Drop Primary key
ALTER TABLE Customer_Details
ADD CONSTRAINT Pkey1 PRIMARY KEY (Account_No);
ALTER TABLE Customer_Details
ADD CONSTRAINT Pkey2 PRIMARY KEY (Account_No, Cust_ID);
ALTER TABLE Customer_Details
DROP PRIMARY KEY;
Or
ALTER TABLE Customer_Details
DROP CONSTRAINT Pkey1;
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SQL - ALTER TABLE
Add/Drop Foreign key
ALTER TABLE Customer_Transaction
ADD CONSTRAINT Fkey1 FOREIGN KEY (Account_No)
REFERENCES Customer_Details (Account_No);
ALTER TABLE Customer_Transaction
DROP CONSTRAINT Fkey1
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SQL - DROP TABLE
DROP TABLE
Deletes table structure
Cannot be recovered
Use with caution
DROP TABLE UnqTable;
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Truncate Table
Deleting All Rows of a table
TRUNCATE TABLE Customer_Details
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Index
Indexing involves forming a two dimensional matrix completely
independent of the table on which index is created.
Here one column will hold the sorted data of the column which is been
indexed
Another column called the address field identifies the location of the record
i.e. Row ID.
Row Id indicates exactly where the record is stored in the table.
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Index
Syntax
Index on a single column
CREATE UNIQUE INDEX Cust_Idx
ON Customer_Details (Cust_ID);
Index on Multiple Column
CREATE UNIQUE INDEX ID_AccountNo_Idx
ON Customer_Details (Cust_ID, Account_No);
Drop a Index
DROP INDEX ID_AccountNo_Idx;
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Index
Advantages of having an INDEX:
Greatly speeds the execution of SQL statements with search conditions
that refer to the indexed column(s)
It is most appropriate when retrieval of data from tables are more frequent
than inserts and updates
Disadvantages of having an INDEX:
It consumes additional disk space
Additional Overhead on DML Statements
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SQL-DML
Here we will discuss about commands using which data from the tables would be extracted and
updated in different ways
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SQL - INSERT INTO
Syntax:
INSERT INTO tablename (Columnlist) VALUES (value list)
Single-row insert with values for all Columns
INSERT INTO Customer_Details
VALUES (106, 'Costner', 'A.', 'Kevin', 3350, 'Savings', 'Indus Bank',
'[e-mail]')
Inserting one row, few columns at a time
INSERT INTO Customer_Details
(Cust_ID, Cust_Last_Name, Cust_Mid_Name, Cust_First_Name, Account_No,
Account_Type, Bank_Branch)
VALUES (107, 'Robert', 'B.', 'Dan', 3351, 'Savings', 'Indus Bank')
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In the first format, we would pass values for all the columns in exactly the same order in which they
appear in the table
When we wish to insert values only for few selected columns. For e.g in a Customer table, we may
know only the Cust_Id, Cust_Last_Name, Cust_Mid_Name, Cust_First_Name, Account_No,
Account_Type Bank_Branch and but not the emailid. So, we may insert only values for Cust_Id,
Cust_Last_Name, Cust_Mid_Name, Cust_First_Name, Account_No, Account_Type and
Bank_Branch columns in this case. The value of the remaining column will be represented as NULL
by default.
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SQL - INSERT INTO
Inserting NULL Value into a Column
INSERT INTO Customer_Details
(Cust_ID, Cust_Last_Name, Cust_Mid_Name, Cust_First_Name, Account_No,
Account_Type, Bank_Branch)
VALUES (108, 'Robert', 'B.', 'Dan', 3352, 'Savings', 'Indus Bank')
Or
INSERT INTO Customer_Details
(Cust_ID, Cust_Last_Name, Cust_Mid_Name, Cust_First_Name, Account_No,
Account_Type, Bank_Branch,Cust_Email)
VALUES (108, 'Robert', 'B.', 'Dan', 3352, 'Savings', 'Indus Bank,NULL)
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SQL - INSERT INTO
Inserting Many rows from a Different Table
INSERT INTO OldCust_details
(Account_No, Transaction_Date,Total_Available_Balance_in_Dollars)
SELECT Account_No,Transaction_Date,Total_Available_Balance_in_Dollars
From Customer_Transaction
WHERE Total_Available_Balance_in_Dollars > 10000.00
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SQL - DELETE FROM
With or without WHERE clause
Syntax: DELETE FROM tablename WHERE condition
Deleting All Rows
DELETE FROM Customer_Details
Deleting Specific Rows
DELETE
FROM Customer_Details
WHERE Cust_ID = 102
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Difference Between Delete and Truncate
DELETE
TRUNCATE
Data can be recovered
Data cannot be recovered.
DML statement
DDL statement
DELETE does not do so
TRUNCATE releases the memory
occupied by the records of the table
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SQL - UPDATE
Syntax:
UPDATE tablename SET column_name =value [ WHERE condition]
Updating All Rows
UPDATE Customer_Fixed_Deposit
SET Rate_of_Interest_in_Percent = NULL;
Updating Particular rows
UPDATE Customer_Fixed_Deposit
SET Rate_of_Interest_in_Percent = 7.3
WHERE Amount_in_Dollars > 3000;
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SQL - UPDATE
Updating Multiple Columns
UPDATE Customer_Fixed_Deposit
SET Cust_Email = [e-mail] ,
Rate_of_Interest_in_Percent = 7.3
WHERE Cust_ID = 104
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Retrieving All columns from a table
To select set of column names,
SELECT column1, column2, FROM TableName
Example
SELECT *
FROM Customer_Details;
Or
SELECT Cust_ID, Cust_Last_Name, Cust_Mid_Name, Cust_First_Name,
Account_No, Account_Type, Bank_Branch, Cust_Email
FROM Customer_Details;
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Examples:
Get the first name of all the customers
SELECT Cust_First_Name FROM Customer_Details;
Get the first name and bank branch of all the customers
SELECT Cust_First_Name, Bank_Branch FROM S
Get full details for all customers in Customer_Details table
SELECT * FROM Customer_Details;
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Retrieving Few Columns
SELECT Cust_ID, Account_No
FROM Customer_Details;
Implementing Customized Columns Names
SELECT Account_No AS Customer Account No.,
Total_Available_Balance_in_Dollars AS Total Balance
FROM Customer_Transaction;
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SQL - ALL, DISTINCT
Get all Customers Name:
SELECT ALL Cust_Last_Name
FROM Customer_Details;
Or
SELECT Cust_Last_Name
FROM Customer_Details;
Get all distinct Customer Name
SELECT DISTINCT Cust_Last_Name
FROM Customer_Details;
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Distinct will filter repetitive occurrence of a particular value
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Retrieving a subset of rows
For retrieval of rows based on some condition, the syntax is
SELECT COL1,COL2,.........
FROM TABLE NAME
WHERE < SEARCH CONDITION>
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Retrieving a subset of rows (Working of WHERE Clause)
Problem Statement: To select rows which have 102 in the Manager column.
Row selection with the WHERE clause
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Relational operators
List all customers with an account balance > $10000
SELECT Account_No, Total_Available_Balance_in_Dollars
FROM Customer_Transaction
WHERE Total_Available_Balance_in_Dollars > 10000.00;
List the Cust_ID, Account_No of Graham
SELECT Cust_ID, Account_No
FROM Customer_Details
WHERE Cust_First_Name = Graham;
Relational operators = , < , > , <= , >= , != or < >
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Relational operators
List all Account_No where Total_Available_Balance_in_Dollars is atleast
$10000.00
SELECT Account_No
FROM Customer_Transaction
WHERE Total_Available_Balance_in_Dollars >= 10000.00;
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Logical operators
List all Cust_ID, Cust_Last_Name where Account_type is Savings and
Bank_Branch is Capital Bank.
SELECT Cust_ID, Cust_Last_Name
FROM Customer_Details
WHERE Account_Type = Savings AND Bank_Branch = Capital Bank;
List all Cust_ID, Cust_Last_Name where neither Account_type is
Savings and nor Bank_Branch is Capital Bank
SELECT Cust_ID, Cust_Last_Name
FROM Customer_Details
WHERE NOT Account_Type = Savings AND
NOT Bank_Branch = Capital Bank;
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Logical operators
List all Cust_ID, Cust_Last_Name where either Account_type is Savings
or Bank_Branch is Capital Bank.
SELECT Cust_ID, Cust_Last_Name
FROM Customer_Details
WHERE Account_Type = Savings OR Bank_Branch = Capital Bank;
Logical operator: AND, OR, and NOT
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Retrieval using BETWEEN
List all Account_Nos with balance in the range $10000.00 to $20000.00.
SELECT Account_No
FROM Customer_Transaction
WHERE Total_Available_Balance_in_Dollars >= 10000.00
AND Total_Available_Balance_in_Dollars <= 20000.00;
Or
SELECT Account_No
FROM Customer_Transaction
WHERE Total_Available_Balance_in_Dollars
BETWEEN 10000.00 AND 20000.00;
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Retrieval using IN
List all customers who have account in Capital Bank or Indus Bank.
SELECT Cust_ID
FROM Customer_Details
WHERE Bank_Branch = Capital Bank
OR Bank_Branch = Indus Bank;
Or
SELECT Cust_ID
FROM Customer_Details
WHERE Bank_Branch IN (Capital Bank, Indus Bank);
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Retrieval using LIKE
List all Accounts where the Bank_Branch begins with a C and has
a as the second character
SELECT Cust_ID, Cust_Last_Name, Account_No
FROM Customer_Details
WHERE Bank_Branch LIKE Ca%;
List all Accounts where the Bank_Branch column has a as the
second character.
SELECT Cust_ID, Cust_Last_Name, Account_No
FROM Customer_Details
WHERE Bank_Branch LIKE _a%;
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SQL - Retrieval using IS NULL
List employees who have not been assigned a Manager yet.
SELECT Employee_ID
FROM Employee_Manager
WHERE Manager_ID IS NULL;
List employees who have been assigned to some Manager.
SELECT Employee_ID
FROM Employee_Manager
WHERE Manager_ID IS NOT NULL;
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SQL - Sorting your results
(ORDER BY)
List the customers account numbers and their account balances, in the
increasing order of the balance
SELECT Account_No, Total_Available_Balance_in_Dollars
FROM Customer_Transaction
ORDER BY Total_Available_Balance_in_Dollars;
by default the order is ASCENDING
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Retrieval using ORDER BY
List the customers and their account numbers in the decreasing order of the
account numbers.
SELECT Cust_Last_Name, Cust_First_Name, Account_No
FROM Customer_Details
ORDER BY 3 DESC;
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Retrieval using ORDER BY
List the customers and their account numbers in the decreasing order of the
Customer Last Name and increasing order of account numbers.
SELECT Cust_Last_Name, Cust_First_Name, Account_No
FROM Customer_Details
ORDER BY Cust_Last_Name DESC, Account_No;
Or
SELECT Cust_Last_Name, Cust_First_Name, Account_No
FROM Customer_Details
ORDER BY 1 DESC, 3;
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Aggregate Functions
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SQL - Aggregate functions
Used when information you want to extract from a table has to do with the
data in the entire table taken as a set.
Aggregate functions are used in place of column names in the SELECT
statement
The aggregate functions in sql are :
SUM( ) , AVG( ) , MAX( ) , MIN( ), COUNT( )
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Aggregate function - MIN
Returns the smallest value that occurs in the specified column
Column need not be numeric type
List the minimum account balance.
SELECT MIN (Total_Available_Balance_in_Dollars)
FROM Customer_Transaction;
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Aggregate function - MAX
Returns the largest value that occurs in the specified column
Column need not be numeric type
Example:
List the maximum account balance.
SELECT MAX (Total_Available_Balance_in_Dollars)
FROM Customer_Transaction;
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Aggregate function - AVG
Returns the average of all the values in the specified column
Column must be numeric data type
Example:
List the average account balance of customers.
SELECT AVG (Total_Available_Balance_in_Dollars)
FROM Customer_Transaction;
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Aggregate function - SUM
Adds up the values in the specified column
Column must be numeric data type
Value of the sum must be within the range of that data type
Example:
List the minimum and Sum of all account balance.
SELECT MIN (Total_Available_Balance_in_Dollars),
SUM (Total_Available_Balance_in_Dollars)
FROM Customer_Transaction;
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Aggregate function - COUNT
Returns the number of rows in the table
List total number of Employees.
SELECT COUNT (*)
FROM Employee_Manager;
List total number of Employees who have been assigned a Manager.
SELECT COUNT (Manager_ID)
Manager_ID)
FROM Employee_Manager;
Employee_Manager;
Count(*)
Count(ColumnName)
=
=
No of rows
No. of rows that do not have NULL Value
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Aggregate function - COUNT
List total number of account holders in the Capital Bank Branch.
SELECT COUNT (*)
FROM Customer_Details
WHERE Bank_Branch = Capital Bank;
List total number of unique Customer Last Names.
SELECT COUNT (DISTINCT Cust_Last_Name)
Cust_Last_Name)
FROM Customer_Details;
Customer_Details;
Count(*)
Count(ColumnName)
=
=
No of rows
No. of rows that do not have NULL Value
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Summary of basic DDL and DML
Create , Alter and Drop are the DDL commands
Update, Insert into, Delete from are the basic DML commands that add or
remove data from tables
Select statement in its various flavours is used to retrieve information from the
table
Aggregate functions work on all the rows of the table taken as a group (based
on some condition optionally)
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Thank You!
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