This document provides an introduction to selecting data from database tables in SQL. It discusses running SQL scripts, what a database table is, the basic SELECT statement syntax to retrieve data from a table including columns, filters, grouping and having. It also covers data types, primary keys, column aliases, and unlocking other user schemas.

1. 3. Select part-1 : Getting started
• Revisit connections and scripts
• First Select ( and what is a table?! )
• All columns or some columns
• Data Types
• Aliases
• Primary keys
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2. Running scripts
SQL*Plus: @”..full_path../my_query.sql”
SQL Developer
SQLFiddle
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3. What is a table?
One of the basic database object types
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14 Rows
8 Columns

4. Select statement
Used to “read”data from the database
**No changes are being made to the data
Select [* | column_list ]
From <table_name>
Where <filter_conditions>
Group by <group columns>
Having <filters on groups>
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5. Wild card v/s columns
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*  all columns Specific columns
Structure (shift+f4)

6. Data types
Describe what kind of data a column has.
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Column Name Datatype (length/precision)

7. List of Oracle Data types
http://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm#i16209
• Character
– char (fixed length string) eg. Char(10) – “Hello “
– varchar2( variable length string) eg. Varchar2(10) – “Hello”
– and more…
• Numeric
– Number. Eg 123.50
– and more..
• Date
– Date eg. 15-aug-1947 00:02:00 AM (includes time component)
– Timestamp eg. 15-aug-1947 00:02:00.155 AM
• and more…
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8. Primary Key
• Uniquely identifies the row in a table.
Check the constraints section in the table definition.
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Use SHIFT+F4
shortcut key for
SQL Developer and
F4 if you are using
Toad.

9. (column) Aliases
• More readable, meaningful and useful column headers.
• Very useful when dealing with complex names or
generating reports
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10. (column) Aliases
• Useful when you want contextual and meaningful names
This kind of join is called a self-join where we join a table (emp) with itself. We’ll cover this
in more detail in the JOINS Chapter.
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Same column
different heading
based on
context/meaning

11. Unlocking other schemas
List of user account present in the database
Conn / as sysdba
Select username from dba_users
Demo Accounts : http://docs.oracle.com/cd/E11882_01/server.112/e10831/installation.htm
Unlocking acccounts:
Conn / as sysdba
Alter user hr identified by “hr”;
Alter user oe identified by “oe”;
Alter user pm identified by “pm”;
Alter user sh identified by “sh”;
Alter user ix identified by “ix”;
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