Database Queries

Select Command

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

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

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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"