{"id":503,"date":"2015-12-10T10:43:32","date_gmt":"2015-12-10T03:43:32","guid":{"rendered":"http:\/\/www.sqlitetutorial.net\/?page_id=503"},"modified":"2022-04-03T15:22:37","modified_gmt":"2022-04-03T08:22:37","slug":"sqlite-avg","status":"publish","type":"page","link":"https:\/\/www.sqlitetutorial.net\/sqlite-avg\/","title":{"rendered":"SQLite AVG"},"content":{"rendered":"\r\n

Summary<\/strong>: in this tutorial, you will learn how to use the SQLite AVG<\/code> function to calculate the average value of a set of values.<\/p>\r\n\r\n\r\n\r\n

Introduction to SQLite AVG function<\/h2>\r\n\r\n\r\n\r\n

The AVG<\/code> function is an aggregate function<\/a> that calculates the average value of all non-NULL values<\/strong> within a group.<\/p>\r\n\r\n\r\n\r\n

The following illustrates the syntax of the AVG<\/code> function:<\/p>\r\n\r\n\r\n

AVG([ALL | DISTINCT] expression);<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
By default, the AVG<\/code> function uses ALL<\/code> clause whether you specify it or not. It means the AVG function will take all non-NULL values when it calculates the average value.<\/p>\r\n\r\n\r\n\r\n
If a column stores mixed data types<\/a> such as integer, real, BLOB, and text, SQLite AVG<\/code> function interprets the BLOB that does not look like a number as zero (0).<\/p>\r\n\r\n\r\n\r\n
The value of the AVG<\/code> function is always a floating point value or a NULL<\/code> value. The AVG<\/code> function only returns a NULL<\/code> value if and only if<\/em> all values in the group are NULL<\/code> values.<\/p>\r\n\r\n\r\n\r\n
You can take a quick test to see how the SQLite function works with various data types.<\/p>\r\n\r\n\r\n\r\n
First, create a new table<\/a> named avg_tests<\/code> using the following statement:<\/p>\r\n\r\n\r\n
CREATE<\/span> TABLE<\/span> avg_tests (val);<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
Next, insert<\/a> some mixed values into the avg_tests<\/code> table.<\/p>\r\n\r\n\r\n
INSERT<\/span> INTO<\/span> avg_tests (val)\r\nVALUES<\/span>\r\n (1<\/span>),\r\n (2<\/span>),\r\n (10.1<\/span>),\r\n (20.5<\/span>),\r\n ('8'<\/span>),\r\n ('B'<\/span>),\r\n (NULL<\/span>),\r\n (x'0010'<\/span>),\r\n (x'0011'<\/span>);<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
Then, query data<\/a> from the avg_tests<\/code> table.<\/p>\r\n\r\n\r\n
SELECT<\/span> rowid<\/span>,\r\n       val\r\n  FROM<\/span> avg_tests;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
After that, you can use the AVG<\/code> function to calculate the average of the first four rows that contain only numeric values.<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\tavg<\/span>(val)\r\nFROM<\/span>\r\n\tavg_tests\r\nWHERE<\/span>\r\n\trowid<\/span> < 5<\/span>;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
Finally, apply the AVG<\/code> function to all the values in the val<\/code> column of the avg_tests<\/code> table.<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\tavg<\/span>(val)\r\nFROM<\/span>\r\n\tavg_tests;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
You have 9 rows in the avg_tests<\/code> table. The row 7 is NULL<\/code>. Therefore, when calculating the average, the AVG<\/code> function ignores it and takes 8 rows into the calculation.<\/p>\r\n\r\n\r\n\r\n
The first four rows are the integer and real values: 1,2, 10.1, and 20.5. The SQLite AVG function uses those values in the calculation.<\/p>\r\n\r\n\r\n\r\n
The 5th and 6th row are text type because we inserted the as ‘B’ and ‘8’. Because 8 looks like a number, therefore SQLite interprets B as 0 and ‘8’ as 8.<\/p>\r\n\r\n\r\n\r\n
The 8th and 9th rows are BLOB<\/code> types that do not look like numbers, therefore, SQLite interprets these values as 0.<\/p>\r\n\r\n\r\n\r\n
The AVG(cal)<\/code> expression uses the following formula:<\/p>\r\n\r\n\r\n
AVG(val) = (1 + 2 + 10.1 + 20.5 + 8 + 0 + 0 + 0 )\/ 8 = 5.2<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
Let’s see how the DISTINCT<\/code> clause works.<\/p>\r\n\r\n\r\n\r\n
First, insert a new row into the avg_tests<\/code> table with a value already exists.<\/p>\r\n\r\n\r\n
INSERT<\/span> INTO<\/span> avg_tests (val)\r\nVALUES<\/span> (10.1<\/span>);<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
Second, apply the AVG<\/code> function without DISTINCT<\/code> clause:<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\tavg<\/span>(val)\r\nFROM<\/span>\r\n\tavg_tests;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
Third, add the DISTINCT<\/code> clause to the AVG<\/code> function:<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\tavg<\/span>(DISTINCT<\/span> val)\r\nFROM<\/span>\r\n\tavg_tests;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
Because the avg_tests<\/code> table has two rows with the same value 10.1, the AVG(DISTINCT)<\/code> takes only the one row for calculation. Therefore, you got a different result.<\/p>\r\n\r\n\r\n\r\n
SQLite AVG function practical examples<\/h2>\r\n\r\n\r\n\r\n
We will use the tracks<\/code> table in the sample database<\/a> for the demonstration.<\/p>\r\n\r\n\r\n\r\n
\"\"<\/figure>\r\n\r\n\r\n\r\n
To calculate the average length of all tracks in milliseconds, you use the following statement:<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\tavg<\/span>(milliseconds)\r\nFROM<\/span>\r\n\ttracks;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
SQLite AVG function with GROUP BY clause<\/h3>\r\n\r\n\r\n\r\n
To calculate the average length of tracks for every album, you use the AVG<\/code> function with the GROUP BY<\/a><\/code> clause.<\/p>\r\n\r\n\r\n\r\n
First, the GROUP BY<\/code> clause groups a set of tracks by albums. Then, the AVG<\/code> function calculates the average length of tracks for each album.<\/p>\r\n\r\n\r\n\r\n
See the following statement.<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\talbumid,\r\n\tavg<\/span>(milliseconds)\r\nFROM<\/span>\r\n\ttracks\r\nGROUP<\/span> BY<\/span>\r\n\talbumid;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
SQLite AVG function with INNER JOIN clause example<\/h3>\r\n\r\n\r\n\r\n
To get the album title together with the albumid<\/code> column, you use the INNER JOIN<\/a> clause in the above statement like the following query:<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\ttracks.AlbumId,\r\n\tTitle,\r\n\tround<\/span>(avg<\/span>(Milliseconds), 2<\/span>) avg_length\r\nFROM<\/span>\r\n\ttracks\r\nINNER<\/span> JOIN<\/span> albums ON<\/span> albums.AlbumId = tracks.albumid\r\nGROUP<\/span> BY<\/span>\r\n\ttracks.albumid;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
Notice that we used the ROUND<\/code> function to round the floating value to 2 digits to the right of the decimal point.<\/p>\r\n\r\n\r\n\r\n
SQLite AVG function with HAVING clause example<\/h3>\r\n\r\n\r\n\r\n
You can use either the AVG<\/code> function or its column’s alias in the HAVING clause<\/a> to filter groups. The following statement only gets the albums whose average length are between 100000 and 200000.<\/p>\r\n\r\n\r\n
SELECT<\/span>\r\n\ttracks.albumid,\r\n\ttitle,\r\n\tround<\/span>(avg<\/span>(milliseconds),2<\/span>)  avg_leng\r\nFROM<\/span>\r\n\ttracks\r\nINNER<\/span> JOIN<\/span> albums ON<\/span> albums.AlbumId = tracks.albumid\r\nGROUP<\/span> BY<\/span>\r\n\ttracks.albumid\r\nHAVING<\/span>\r\n\tavg_leng BETWEEN<\/span> 100000<\/span> AND<\/span> 200000<\/span>;<\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
\"SQLite<\/figure>\r\n\r\n\r\n\r\n
In this tutorial, we have shown you how to use the SQLite AVG<\/code> function to calculate the average values of non-NULL values in a group.<\/p>\r\n
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In case you want to calculate the average value of distinct (or unique) values, you need to specify the DISTINCT<\/a> clause explicitly in expression.<\/p>\r\n\r\n\r\n\r\n