Guide to Oracle SQL (University at Buffalo Version)

Maintaining a Database using SQL Statements

Oracle uses the Structured Query Language (SQL) to create and maintain the database and tables. SQL [rovides statements that allow database administrators and users to perform create, read, update, and delete (CRUD) operations on a database. SQL is broken down into four (4) areas: a data query language (DQL), a data definition language (DDL), a data control language (DCL), and a data manipulation language (DML). SQL statements are not case-sensitive. I almost always try to upper case my SQL statements just for readability. I also try to use camel-case fo my database, table, and field names. For example, employeeTable and firstName.

To use Oracle on your local machine, you need to download Oracle Database Express 18c page. After you install 18c, then you can download and install SQL Developer.

If you are using SQL Developer, then right-click on your connection in the SQL developer Connections window. To create a new connection, click the "plus-sign" icon in the "Oracle Connections" pane. Then, you may have to change the connect type from "Basic" to "TNS".

Then choose Open SQL Worksheet. This is where you can enter SQL statements.

The CREATE Statement

The SQL CREATE statement can be used to create a new database or a new table within an existing database if you have permissions that allow you to create a new database.

The CREATE DATABASE Statement

The SQL CREATE DATABASE databaseName statement can be used to create a new database.

  CREATE DATABASE jimTest;
  
  Database JIMTEST created.
  

The CREATE TABLE Statement

The SQL CREATE TABLE tableName statement can be used to create a new table within an existing database.

CREATE TABLE jimTable (
  jimID NUMBER(9),
  firstName VARCHAR2(25) NOT NULL,
  lastName VARCHAR2(25) NOT NULL,
  CONSTRAINT pk_jimID PRIMARY KEY (jimID)
  );
  
  Table JIMTABLE created.

The DROP TABLE Statement

The SQL DROP TABLE tableName statement can be used to delete a within an existing database.

DROP TABLE jimTable
  
  Table "JIMTABLE" dropped.

The DESCRIBE Statement

In SQL Developer pressing the SHIFT-F4 key displays the table structure.

DESCRIBE jimTable;
  
    COLUMN_NAME DATA_TYPE         NULLABLE DATA_DEFAULT COLUMN_ID Comments  
1 JIMID       NUMBER(9,0)          No                      1 
2 FIRSTNAME   VARCHAR2(25 BYTE)    No                      2 
3 LASTNAME    VARCHAR2(25 BYTE)    No                      3

The INSERT Statement

The INSERT statement is used to add a record to a table. String (VARCHAR2) values should be enclosed in single quotes (''). In SQL Developer, if you are entering multiple statements you need to highlight all the statements before clicking the run icon ().

INSERT INTO jimTable 
(jimID, firstName, lastName)
VALUES
(1, 'Jim', 'Gerland');
INSERT INTO jimTable
(jimID, firstName, lastName)
VALUES
(2, 'Phil', 'Phailure');
INSERT INTO jimTable 
(jimID, firstName, lastName)
VALUES
(3, 'Sally', 'Smart');
  
1 row inserted.
  
1 row inserted.
  
1 row inserted.

In SQL Developer, click the Commit () icon to apply the results of your INSERT query to your database.

The SELECT Statement

The SELECT statement is used to retreive information from the database.

Using the SELECT Statement To Retreive Records

The asterisk (*) is used as a wildcard. It is used to retreive all the fields in the table.

SELECT * 
FROM jimTable;
  
  JIMID FIRSTNAME LASTNAME  
1 1     Jim       Gerland
2 2     Phil      Phailure
3 3     Sally     Smart

If you click the run script icon () in SQL developer you get a different type of output.

SELECT * 
FROM jimTable;
  

Using the SELECT Statement To Retrieve Certain Fields

You can also name the fields you would like return using the SELECT field[s] statement.

SELECT firstName, lastName 
FROM jimTable

  FIRSTNAME LASTNAME  
1 Jim       Gerland
2 Phil      Phailure
3 Sally     Smart
  

The UPDATE Statement

The UPDATE statement can be used to modify an existing record in a table.

UPDATE jimtable 
SET firstName = 'James' 
WHERE jimID = 1;

1 row updated.

The DELETE Statement

The DELETE statement can be used to remove an existing record from a table.

DELETE FROM jimtable 
WHERE jimID = 1;

1 row deleted.

The TRUNCATE Statement

The TRUNCATE statement is used to remove all the records in a table but keep the strucure (fields) of the table intact.

TRUNCATE TABLE jimTable;
  
TABLE JIMTABLE truncated.

SQL Comments

It is important to comment your SQL code. This helps you when you need to go back and modify your code and it helps other devlopers who will need to maintain you code after you move on to new, more challenging projects. SQL provides two (2) types of comments. single line comments (--) and multiple line comments (/* */).

-- This is a single line comment
/* 
  This is a 
  multiple line 
  comment
*/
SELECT * FROM countries;

   COUNTRY COUNTRY_NAME                    REGION_ID
---------- ------------------------------ ----------
         1 Argentina                               2
         2 Brazil                                  2
         3 Canada                                  2
         4 United States                           2
         5 Mexico                                  2