2nd Day, Introduction to SQL- 10-06-2025

*SQL *- Structured Query Language-

1. used in Data analysis.
2. Software development purpose
3. To manage and manipulate relational DBMS.

*Uses of SQL
*

1. Querying the data. To find a specific information.
2. To insert, update , delete the data.

**SQL commands

**
DDL- Data definition Language.

Used to define/ manage the tables.

The commands are,

1. CREATE- Create a table
2. ALTER- To modify the table structure, which was created already.
3. DROP- To delete the complete table
4. RENAME- To rename the table
5. TRUNCATE- To delete all records except the table structure.

DML- Data manipulation language.

To manipulate the data into the table.

1. INSERT- Add new data in rows.
2. UPDATE- Modify the existing data. 3.DELETE- Remove data from the row.

DQL - Data Query Language

SELECT- To retrieve a data from the table.

( Select* from table name )

DCL- Data control language

• Used for access control

GRANT- To provide access/ privileges to users.
REVOKE- To take back the privileges.

TCL- Transaction control Language

Used to manage the transactions/ data.

COMMIT- used to permanently save any transaction into the database
ROLLBACK- Used to restores the database to the last committed state. undo the changes since last commit
SAVE POINT- Set a point to rollback
SET TRANSACTION- To set the properties for transactions ( Like read only )

DATA TYPES

1. Numeric Type
**
**SMALLINT- It saves whole numbers in the specified range. Memory 2 bytes
INTEGER-It saves whole numbers in the specified range.-Memory 4 bytes
BIGINT- Memory is 8 bytes
NUMERIC @ DECIMAL
REAL@ FLOAT4- Single precision floating point number-

Single-precision floating-point format (sometimes called FP32 or float32) is a computer number format, usually occupying 32 bits in computer memory; it represents a wide dynamic range of numeric values by using a floating radix point.

DOUBLE PRECISION @FLOAT8 - Double-precision floating-point numbers are 64-bit floating-point numbers used to represent real numbers with greater precision and a wider range than single-precision floating-point numbers. This format, often referred to as FP64, is commonly used in scientific computing and other applications where high accuracy is crucial.

*2. CHARACTER
*

CHAR (n)- fixed length character string.

ex, USA,IND

VARCHAR (n)- Lengthy character string.
TEXT- Variable length characteristics.

( unlimited length )

*3. BOOLEAN TYPE
*

TRUE or FALSE.

4. DATE AND TIME TYPES

DATE- date
TIMESTAMP- (date and time )

To launch, psql -h localhost -U postgres

Create- CREATE DATABASE Students ;
drop- DROP DATABASE STUDENTS

TO view DATABASE - \L
To close- \q

alter/ edit - ALTER DATABASE Students RENAME TO Students_details;

\c Students; - to connect the DB.

CREATE TABLE students_info ( Name varchar(50), Class INTEGER, Joining_date DATE);

*to view- \dt
*