Difference between revisions of "Database Queries"

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== Adding Constraints ==
== Adding Constraints ==
  '''This makes customer# the primary key  the constraint name is used so you can easily identify an error if you try to  
  '''This makes customer# the primary key  the constraint name is used so you can easily identify an error if you try to  
enter a duplicate customer'''
enter a duplicate customer'''
  ALTER TABLE customers ADD CONSTRAINT customers_customer#_pk PRIMARY KEY(customer#);
  ALTER TABLE customers ADD CONSTRAINT customers_customer#_pk PRIMARY KEY(customer#);




[[#Select Command|Back To Top]]-[[Main_Page| Home]] - [[Oracle_SQL|Category]]
[[#Select Command|Back To Top]]-[[Main_Page| Home]] - [[Oracle_SQL|Category]]

Revision as of 19:47, 11 October 2017

Select Commands

SELECT * from tableName
 - SELECT all columns FROM the table
SELECT column1, column2 FROM tableName
SELECT 2 columns FROM the tableName table
SELECT DISTINCT column FROM tableName
will display only unique results (no duplicates)
SELECT firstname || ' ' || lastname FROM tablename
will concatenate first and last name into one field (the ' ' between the || inserts a space)
SELECT fristname || ' ' || lastname "Customer Name" FROM table name
this will add a alias for the column heading called Customer Name
SELECT title AS "Title of Book", category FROM books;
This adds the column alias "Title of Book" to the results instead of using just the title as the column heading

select table_name FROM user_tables

that exact statement will list all tables

selecting column names, data type, and default values

select column_name, data_type, data_default from user_tab_columns where table_name = 'ACCTMANAGER'

Creating Calculated Fields in a Query

SELECT title, retail*cost as profit FROM books;
retail column is multiplied by cost and the result is displayed in the alias field profit

Using Concatenation

Creating a table based on another table (subquery)

CREATE TABLE cust_mkt AS (SELECT customers, city, state, zip FROM customers);


SELECT firstname || lastname FROM customers;
this will display the info but last and first names will be together eg. firstlast
to add a space between the names :
SELECT firstname || ' , ' | || lastname as "Customer Name" FROM customers;
this will add the , between the names and give it an alias heading "Customer name"

Adding Constraints

This makes customer# the primary key  the constraint name is used so you can easily identify an error if you try to 

enter a duplicate customer

ALTER TABLE customers ADD CONSTRAINT customers_customer#_pk PRIMARY KEY(customer#);


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