COUNT « Aggregate Functions « SQL / MySQL
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SQL / MySQL
Get the number of items for each type of wood
Get the number of woods for each type of item
How many times did drivers travel more than 200 miles in a day?
COUNT and GROUP BY
Count by group
COUNT(expr) doesn't count NULL values is useful when producing multiple counts from the same set of values.
The different forms of COUNT( ) can be very useful for counting missing values
Put the COUNT( ) expression in a HAVING clause instead.
Tracking Down Duplicates
Queries counting duplicate records have the following form
Counting and Identifying Duplicates
Count number of rows containing duplicated names
To see which names are duplicated in the cat_mailing table, use a summary query that displays the non-unique v
Eliminating Duplicates from a Query Result
Removing Duplicates of a Particular Row
Count duplicate records
How many days did Suzi drive?
How many messages were sent by each message sender
How many states did the United States consist of at the beginning of the 20th century?
Or to count weekend versus weekday trips
Count each value and see which one is most common
Generating Frequency Distributions
Relative frequency distributions
Counting Missing Values
Count them directly using SUM(ISNULL(score)).
Count the total number of rows
Categorizing Non-Categorical Data
Total number of the table vs unique values count
To produce a count-per-author summary that includes even authors with no books in the book table, use a LEFT J
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