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SQL Basics

Joins
Constraints



Oracle SQL Basics


Oracle is a relational database. Relational databases store data in tables like this:

COUNTRY
CTRY_ID CTRY_NAME CTRY_AREA CTRY_POP POP_UPD_AT CURRENCY
14 Germany 137882 82046000 30-nov-08 Euro
48 Ghana 92100 23837000 null Cedi
53 Australia 2969907 21884000 4-sep-09 Australian Dollar
73 Greece 50949 11257285 1-Jan-09 Euro
122 Georgia 26900 4382100 1-Jan-09 Lari
123 New Zealand 104428 4320300 4-sep-09 New Zealand Dollar
147 Gambia 4361 1705000 null Dalasi
149 Gabon 103347 1475000 null CFA franc

Communication with the database is performed using Structured Query Language (SQL).

SQL is used to create, alter and destroy tables in the database and to insert, update, delete and query the data in these tables.

Applications may use APIs and frameworks such as ODBC, JDBC, JPA and Hibernate, but ultimately these will all talk to the database using SQL.

SQL consists of:
  • The SELECT statement
  • Data Manipulation Language (DML)
  • Data Definition Language (DDL)
Let's take a tour of SQL, starting with the SELECT statement.
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