PostreSQL錯誤：函數AVG（字符改變）不存在

Question

我想從一列計算平均數PostgreSQL中

SELECT AVG(col_name) 
From TableName 

它給我這個錯誤：

ERROR: function avg (character varying) does not exist 

LINE 1: SELECT AVG(col_name) 
      ^
HINT: No function matches the given name and argument types. You might need to add explicit type casts. 

Answer 1

商店號碼數字字段，整數，小數或其他。但不在文本/ varchar字段中。

查閱所有numeric data types的手冊。

---

討厭workaound：CAST一些記錄到一個數值，讓別人爲文本。例如：

/* 
create temp table foo AS 
SELECT x FROM (VALUES('x'),('1'),('2')) sub(x); 
*/ 

WITH cte AS (
SELECT 
    CASE 
     WHEN x ~ '[0-9]' THEN CAST(x AS decimal) -- cast to numeric field 
    END AS num, 
    CASE 
     WHEN x ~ '[a-zA-Z]' THEN x 
    END AS a 
FROM foo 
) 
SELECT AVG(num), COUNT(a) FROM cte;