All language subtitles for 1. COUNT

Now, we will be discussing some of the aggregate functions such as count, sum, average
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Min and max
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First is the count function
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Count function will return the count of the expression that you have mentioned
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For example if you want to find out the number of sales that you have done
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You can count the number of sales lines that you have, to get the total number of sales that you are done
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Or you want to find out the count of customers with name starting with A
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Then again count function will help you
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The syntax of count function is
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You select the column names if you want
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Count will be written as count and then you give the column name
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Of the column of which you want the
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Count
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So it will count number of non null values in that column
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After it has applied the condition so if you are mentioned any where clause
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It will check the condition
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And after that if there is any non null value in that particular column which were mentioned after the count
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It will give that particular count
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Let's look at some of the examples to understand this
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So this first example where I have returned select count star from sales
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It will
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Go to the sales table
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And it will
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Look at all the records
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And it will give back the count of all the rows in that particular table
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Let it go and write this in the PG admin interface
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Select
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Count star
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Remember that I put the star
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Within the bracket
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Whatever column name you want to mention you have to put it into bracket, from sales, sales is the table name
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When I run this
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I get a count of
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9994
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This is the total count but if you notice the column name is written as count
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This may not make any sense to anyone who looks at this count that is why we will be using aliases
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And mention
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Count star as
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The total count of sales something like that
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So that we get the right column name
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Now, Imagine if you want to find out
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How many orders that particular customer has given
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And how many products that particular customer has ordered
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Go and look at the
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Sales table
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By just doing select star from sales
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So for example, this first customer with customer ID CG 12520
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It has two entries on the top those two entries have the same order ID
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Which means it was one single order
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In which two different products were ordered so the product ID in both these
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Two rows is different
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If I want to find out
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Count of all the orders that this particular customer has given
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And the count of different products that this customer has ordered
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I start typing
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Select
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And select the count of
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Order lines
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So each separate order line is giving me the number of products that that particular customer has ordered
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So I Name this as
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Number of products ordered
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Then I'll find out
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Count of
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Order IDs
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Distinct order ID
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If I do not write distinct
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Repetitive order IDS will be
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Will be counted multiple Times
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As number of orders
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And
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This will be from the table
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Sales
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Where customer ID
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Will be this CG 12520
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CG12520
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CG12520
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Select this query and run it
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You can see
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The column names are the ones
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That we provided
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And
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This particular customer
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Ordered three times
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He gave three orders
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But
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One or more of the orders has multiple products in it so
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Total number of products ordered by this customer is 5
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Next we'll look at how to use
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Sum function