mysql - SQL count + join 抛出语法错误，但没有 count 也可以正常工作

Question

我在以下查询中遇到奇怪的语法错误:

SELECT COUNT (*) 
FROM a 
JOIN b ON a.id = b.a_id

但是没有 COUNT 的查询就像一个魅力:

SELECT * 
FROM a 
JOIN b ON a.id = b.a_id

添加 JOIN 规范，如 INNER、LEFT 等 - 没有帮助。

The syntax error doesn't specify exactly what's wrong, just provides certain codes: [42000][1064]

如何修复它？

编辑:

这里是:

SELECT COUNT(customers.*) 
FROM customers 
JOIN customer_behaviour ON customers.id = customer_behaviour.customer_id

删除 COUNT 使其完全有效。这真的很奇怪!

Answer 1

删除 COUNT 和 (*) 之间的空格:

SELECT COUNT(*) FROM a JOIN b ON a.id = b.a_id 
    -- COUNT (*)

<强> DBFiddle Demo

<小时/>

编辑:

SELECT COUNT(customers.*) 
FROM customers 
JOIN customer_behaviour 
  ON customers.id = customer_behaviour.customer_id

-- should be    
SELECT COUNT(*) 
FROM customers 
JOIN customer_behaviour 
  ON customers.id = customer_behaviour.customer_id

-- or
SELECT COUNT(customers.id) 
FROM customers 
JOIN customer_behaviour 
  ON customers.id = customer_behaviour.customer_id

编辑2

Now, can I add DISTINCT to it? Seems like using COUNT (DISTINCT ...) starts throwing the error again!

只需定义列名称即可:

SELECT COUNT(DISTINCT table_name.column_name) 
FROM customers 
JOIN customer_behaviour 
  ON customers.id = customer_behaviour.customer_id