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SQL BASICS
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In this notes, we cover the basics of using SQL to retrieve data stored in relational databases.
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SQL BASICSBasic SQL :
In this video, we cover the basics of using SQL to retrieve data
stored in relational databases. The first thing you need to know
is how to get all the data from one table. To do this in SQL, you
use the SELECT * statement. For example, SELECT * FROM
customers; will retrieve all the data from
the customers table.
Note that there are different data types in SQL, such as strings
and integers. You can also perform aggregation functions like
getting averages or maximum/minimum values.
Filtering Data with the WHERE Clause
If you want to filter the results by a specific condition, you can
use the WHERE clause. For example, SELECT * FROM
customers WHERE customer_name='Alfred\'s
Futterkist'; will retrieve all the columns for the customer
with the name 'Alfred's Futterkist'.
You can use the % sign as a wildcard to match patterns. For
example, SELECT * FROM customers WHERE customer_name
LIKE 'Alf%'; will match any customer whose name starts
with 'Alf'.
Pattern Matching and Aggregations in SQL
SQL offers a variety of operations, including pattern matching
and aggregations, to data scientists. Pattern matching is not
case sensitive and can be used with other types of data, but is
often used with dates. For example,
selecting start from orders where order date is between
"1996" and "1997" will return all of the data from 1997 but not
from 1996. Aggregations, such as avg , count , min ,
and max , are used to compute numerical values from data.
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