This function has none of DETERMINISTIC, NO SQL..... (you *might* want to use the less safe log_bin_t

Origin of problem ：

topic ：

 surface : Employee

+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| salary      | int  |
+-------------+------+
Id Is the primary key column of the table .
 Each row of the table contains information about the employee's salary .

 

 Write a SQL Query to report  Employee  No  n  High wages . If there is no  n  A maximum wage , The query should be reported as  null .

 The query result format is as follows .

 

 Example  1:

 Input : 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
n = 2
 Output : 
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200                    |
+------------------------+

 Example  2:

 Input : 
Employee  surface :
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
+----+--------+
n = 2
 Output : 
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| null                   |
+------------------------+

 source ： Power button （LeetCode）
 link ：https://leetcode-cn.com/problems/nth-highest-salary
 Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

Explain ：

--  function 
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
    set N = N - 1;
  RETURN (
    select ifnull((select distinct Salary from Employee order by Salary desc limit N,1),null)
    as getNthHighestSalary
  );
END
--  perform 
select getNthHighestSalary(2)

Problems arise ：

Problem analysis ：

That's because it turns on bin-log journal , We must determine the following points in the function

deterministic Not sure of

no sql No, SQL sentence

reads sql data Read only data

modifies sql data Modifying data

contains sql contain SQL sentence

Because in function in , Only deterministic ,no sql,reads sql data Be supported . So open bin-log Must be after function Specify the parameters

Problem solving ：

show variables like ‘log_bin_trust_function_creators’;

set global log_bin_trust_function_creators = 1

show variables like ‘log_bin_trust_function_creators’;

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
    set N = N - 1;
  RETURN (
    select ifnull((select distinct Salary from Employee order by Salary desc limit N,1),null)
    as getNthHighestSalary
  );
END

select getNthHighestSalary(2)

Add ：

Using the above method will fail after the database is restarted , The following methods can be used for long-term effectiveness

[email protected]_zxy ~]# vim /etc/my.cnf

Add at the end

log_bin_trust_function_creators = 1