SQL Query

SQL Query
Getting to the data …….

Objectives
 DDL vs. DML
 DML Statements

SQL Language
 DDL - DDL is abbreviation of Data Definition Language. It is used to create and modify the structure
of database objects in database.
 Examples: CREATE, ALTER, DROP statements
 DML - DML is abbreviation of Data Manipulation Language. It is used to retrieve, store, modify,
delete, insert and update data in database.
 Examples: SELECT, UPDATE, INSERT statements
 DCL - DCL is abbreviation of Data Control Language. It is used to create roles, permissions, and
referential integrity as well it is used to control access to database by securing it.
 Examples: GRANT, REVOKE statements
 TCL - TCL is abbreviation of Transactional Control Language. It is used to manage different
transactions occurring within a database.
 Examples: COMMIT, ROLLBACK statements

Data Manipulation Language (DML)
 The verbs for the basic SQL commands are:
 SELECT - to retrieve (query) data
 UPDATE - to modify existing data
 DELETE - to modify existing data
 INSERT - to add new data
 We further break down SQL commands into the following categories:
 Data Creation
 Data Manipulation
 Data Retrieval
 Advanced SQL with JOINS, Subqueries and UNIONS

Systems Development
Life Cycle
Project Identification
and Selection
Project Initiation
and Planning
Analysis
Physical Design
Implementation
Maintenance
Logical Design
Enterprise modeling
Conceptual data modeling
Logical database design
Physical database design
and definition
Database implementation
Database maintenance
Database
Development Process

SQL Database Definition
 Data Definition Language (DDL)
 Major CREATE statements:
 CREATE SCHEMA – defines a portion of the database owned by a particular user
 CREATE TABLE – defines a table and its columns
 CREATE VIEW – defines a logical table from one or more views
 Other CREATE statements: CHARACTER SET, COLLATION, TRANSLATION, ASSERTION, DOMAIN

SQL - Insert
 The SQL INSERT INTO clause is used to insert data into a SQL table. The SQL INSERT INTO is
frequently used and has the following generic syntax:
 The SQL INSERT INTO clause has actually two parts - the first specifying the table we are inserting
into and giving the list of columns we are inserting values for, and the second specifying the values
inserted in the column list from the first part.
INSERT INTO Table1 (Column1, Column2, Column3)
VALUES (ColumnValue1, ColumnValue2, ColumnValue3)

SQL - Insert
 Inserting a record with all fields
 INSERT INTO CUSTOMER_T VALUES (001, ‘Contemporary Casuals’, 1355 S. Himes Blvd.’,
‘Gainesville’, ‘FL’, 32601);
 Inserting a record with specified fields
 INSERT INTO PRODUCT_T (PRODUCT_ID, PRODUCT_DESCRIPTION, PRODUCT_FINISH,
STANDARD_PRICE, PRODUCT_ON_HAND) VALUES (1, ‘End Table’, ‘Cherry’, 175, 8);
 Inserting records from another table
 INSERT INTO CA_CUSTOMER_T SELECT * FROM CUSTOMER_T WHERE STATE = ‘CA’;

SQL – Delete
 The SQL DELETE Query is used to delete the existing records from a table.
 You can use WHERE clause with DELETE query to delete selected rows, otherwise all the records
would be deleted.
 Removes rows from a table
 Delete certain rows
 DELETE FROM CUSTOMER_T WHERE STATE = ‘HI’;
 Delete all rows
 DELETE FROM CUSTOMER_T;

SQL - Drop
 The SQL DROP TABLE statement is used to remove a table definition and all data, indexes, triggers,
constraints, and permission specifications for that table.
 NOTE: You have to be careful while using this command because once a table is deleted then all the
information available in the table would also be lost forever.
 The SQL TRUNCATE TABLE command is used to delete complete data from an existing table.
 You can also use DROP TABLE command to delete complete table but it would remove complete
table structure form the database and you would need to re-create this table once again if you wish
you store some data.

SQL - Update
 The SQL UPDATE command is used to modify data stored in database tables.
 Modifies data in existing rows
UPDATE PRODUCT_T
SET UNIT_PRICE = 775
WHERE PRODUCT_ID = 7;

SQL - Select
 SQL SELECT is without a doubt the most frequently used SQL command that's why we are starting
our tutorial with it. The SQL SELECT command is used to retrieve data from one or more database
tables.
 Clauses of the SELECT statement:
 SELECT - List the columns (and expressions) that should be returned from the query
 FROM - Indicate the table(s) or view(s) from which data will be obtained
 WHERE - Indicate the conditions under which a row will be included in the result
 GROUP BY - Indicate columns to group the results
 HAVING - Indicate the conditions under which a group will be included
 ORDER BY - Sorts the result according to specified columns

SQL Statement processing order

SQL Comparison Operators
Operator Meaning
= Equal To
> Greater Than
>= Greater Than or Equal To
< Less Than
<= Less Than or Equal To
<> Not Equal To
!= Not Equal To

SQL Aliases
 SQL aliases are used to give a database table, or a column in a table, a temporary name.
 Basically aliases are created to make column names more readable.
SELECT CUST.CUSTOMER AS NAME, CUST.CUSTOMER_ADDRESS
FROM CUSTOMER_V CUST
WHERE NAME = ‘Home Furnishings’;

SQL Aggregate Functions
 SQL aggregate functions return a single value, calculated from values in a column.
 Useful aggregate functions:
 AVG() - Returns the average value
 COUNT() - Returns the number of rows
 FIRST() - Returns the first value
 LAST() - Returns the last value
 MAX() - Returns the largest value
 MIN() - Returns the smallest value
 SUM() - Returns the sum

SQL Aggregate Functions
 Using the COUNT aggregate function to find totals
 The COUNT(column_name) function returns the number of values (NULL values will not be counted)
of the specified column:
SELECT COUNT(*) FROM ORDER_LINE_V
WHERE ORDER_ID = 1004;

SQL Boolean Operators
 AND, OR, and NOT Operators for customizing conditions in WHERE clause
 The AND operator displays a record if both the first condition AND the second condition are true.
 The OR operator displays a record if either the first condition OR the second condition is true.
SELECT PRODUCT_DESCRIPTION, PRODUCT_FINISH, STANDARD_PRICE
FROM PRODUCT_V
WHERE (PRODUCT_DESCRIPTION LIKE ‘%Desk’
OR PRODUCT_DESCRIPTION LIKE ‘%Table’)
AND UNIT_PRICE > 300;

SQL Between Operator
 The BETWEEN operator selects values within a range. The values can be numbers, text, or dates.
SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

SQL Wildcards
 In SQL, wildcard characters are used with the SQL LIKE operator.
 SQL wildcards are used to search for data within a table.
 With SQL, the wildcards are:
Wildcard Description
% A substitute for zero or more characters
_ A substitute for a single character
[charlist] Sets and ranges of characters to match
[^charlist]
or
[!charlist]
Matches only a character NOT specified within the brackets

SQL Order Clause
 The ORDER BY keyword is used to sort the result-set by one or more columns.
 The ORDER BY keyword sorts the records in ascending order by default. To sort the records in a
descending order, you can use the DESC keyword.
SELECT CUSTOMER_NAME, CITY, STATE
FROM CUSTOMER_V
WHERE STATE IN (‘FL’, ‘TX’, ‘CA’, ‘HI’)
ORDER BY STATE, CUSTOMER_NAME;

SQL Group Clause
 Categorizing results
SELECT STATE, COUNT(STATE)
FROM CUSTOMER_V
GROUP BY STATE;

SQL Having Clause
 For use with GROUP BY
SELECT STATE, COUNT(STATE)
FROM CUSTOMER_V
GROUP BY STATE
HAVING COUNT(STATE) > 1;
 Like a WHERE clause, but it operates on groups (categories), not on individual rows. Here, only
those groups with total numbers greater than 1 will be included in final result

SQL Unions
 The SQL UNION clause/operator is used to combine the results of two or more SELECT statements
without returning any duplicate rows.
 To use UNION, each SELECT must have the same number of columns selected, the same number of
column expressions, the same data type, and have them in the same order, but they do not have to
be the same length.
SELECT column1 [, column2 ]
FROM table1 [, table2 ] [WHERE condition]
UNION
SELECT column1 [, column2 ]
FROM table1 [, table2 ] [WHERE condition]

SQL Distinct
 The SQL DISTINCT keyword is used in conjunction with SELECT statement to eliminate all the
duplicate records and fetching only unique records.
 There may be a situation when you have multiple duplicate records in a table. While fetching such
records, it makes more sense to fetch only unique records instead of fetching duplicate records.
SELECT DISTINCT column1, column2,.....columnN
FROM table_name
WHERE [condition]

Summary
 The Structured Query Language (SQL) defines a standard for interacting with relational
databases
 Most platforms support ANSI-SQL 92
 Most platforms provide many non-ANSI-SQL additions
 Most important data modification SQL statements:
 SELECT: Returning rows
 UPDATE: Modifying existing rows
 INSERT: Creating new rows
 DELETE: Removing existing rows

SQL Query

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