How to Use Functions in SQL
SQL supports simple queries like Select * from names where first = “Neil”, but you can use functions such as sum. SELECT SUM(Quantity * Price) AS total FROM Sales WHERE MONTH(Date)=2
which would select the total sales for February. This uses 2 functions, one is the SUM and the other is the MONTH which extracts just the month from a date. There are other functions such as MAX to find the maximum value, MIN to find the minimum value, AVG to find the average value.
Soundex coding is also present in SQL, and that allows you to compare strings by how they sound. For example
SELECT SOUNDEX (‘Smith’), SOUNDEX (‘Smythe’);
This returns the same value, as trailing e does not always make a difference in the sound of the word, and y and I can be confused. This allows you to find names that are close to the one you are looking for. You can use DIFFERENCE to compare 2 different strings.
You can compare if a value is null with ISNULL, which is useful for detecting possibly invalid values.
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