Fuzzy Data Matching with SQL

Chapter 1. A SELECT Review

This chapter represents a very quick review of SQL elements used throughout this book. In particular, we will cover the following topics:

• Simple SELECT statements (see the next section)

• Common table expressions (see ​)

• In CASE of emergency (see ​)

• Joins (see ​)

These will all be used in examples in the remainder of the book, so let’s take some time and get used to them here.

Simple SELECT Statements

In the beginning was the word, and the word was SELECT. To get anything out of a relational database table, you need SELECT. Here it is in its simplest form (to save space, only the first 10 rows are shown in the result set, and we’re counting DC as a state):

SELECT * FROM crm.CustomerCountByState;

	State	Total
0	AK	6
1	AL	0
2	AR	1
3	AZ	9
4	CA	72
5	CO	9
6	CT	5
7	DC	1
8	DE	0
9	FL	28

That gives us a “raw” dump of all the columns in the table (the *), in whatever order the rows may happen to be stored in the database table (database order).

Now we will switch to a bit “wider” dataset with more columns. Let’s take the top 10 by whatever states happen to sort first in the customer dataset. We’re also going to be choosy about which columns we want and not just grab them all:

SELECT TOP 10   /* Because we only want 10           */
    LastName,
    FirstName,
    City,
    State
FROM crm.NormalizedCustomer
ORDER BY State; -- This is the filter for the TOP 10

	LastName	FirstName	City	State
0	Campain	Roxane	Fairbanks	AK
1	Ferencz	Erick