Overview of Data Analysis
After creating a table and filling it up with some
values, the next step is probably to
see what you can do with data stored in it. One of the most commonly performed operations by the
users of a database is to look for data or to isolate data that responds
to a particular criterion. Looking for data that is conform to a
criterion is referred to as querying.
As a database developer, you perform queries by
passing instructions to the SQL interpreter. This is done using some
special reserved words.
Learning: Introducing Data Analysis
- Open the MySQL prompt
- Execute the following statement:
As we learned in previous lessons, the most fundamental keyword used by SQL is SELECT.
In order to process a request, you must specify what to select. Therefore,
the SELECT keyword uses the following syntax:
SELECT What FROM WhatObject;
||As stated already, SQL is not
case-sensitive. This means that SELECT, Select, and select
represent the same word.
The What factor of our syntax is the name of
the column(s) of a table. The WhatObject factor can be the name of a
table (or a view).
Learning: Performing Data Analysis
To select everything from a table, you can use the asterisk as the range
of values. For example, to display all records, execute the following statement:
SELECT * FROM Students;
As opposed to viewing all data, you can also select one particular
column whose fields you want to view. To do this, you can replace the What
factor in the syntax with the name of the desired column. As an example, execute the following
SELECT LastName FROM Students;
When you execute the statement, it would display only the
column that contains the last names
To consider more than one column in a statement, you can
list them in the What factor of our syntax, separating them with a comma except for the last
column. The syntax you would use is:
SELECT Column1, Column2, Column_n FROM WhatObject;
As an example, to display a list that includes only the
names, gender, and home phone of records from a table called
Students, execute the following statement:
SELECT FirstName, LastName, Gender, HomePhone