MySQL條件取決於列值

Question

因此，我的表中或多或少具有以下列結構：

Name     Age   Operator
----     ---   --------
Jhon      35      >
Michael   30      =
Jess      27      <

基於此，我想進行這樣的查詢

SELECT * FROM mytable WHERE Name = 'John' AND Age > 40

顯然，這將不會返回任何結果，這很好，但是我的問題是我想使用Jhon的“ Operator”值（在本例中為>）來創建該條件。

可能嗎？

謝謝！

Answer 1

您還可以使用MySQL的PREPARE和EXECUTE語句來創建動態SQL。

SET @name = 'Jhon';
SET @operator = NULL;
SET @age = 10;

SELECT 
 Operator
INTO 
 @operator
FROM 
 Table1
WHERE
 Name = @name;

SET @SQL = CONCAT(
   "SELECT"
 , " * "
 , " FROM " 
 , " Table1 "
 , " WHERE "
 , "  name = '", @name, "' AND age ", @operator, ' ' , @age
);

SELECT @SQL; # not needed but you can see the generated SQL code which will be executed

PREPARE s FROM @SQL;
EXECUTE s;

參見演示https://www.db-fiddle.com/f/3Z59Lxaoy1ZXC4kdNCtpsr/1

Answer 2

您可以像這樣簡單地做到這一點：

SELECT
*
FROM Table1
WHERE Name = 'Jhon'AND CASE 
WHEN Operator = '>' THEN Age > 10
WHEN Operator = '<' THEN Age < 10
WHEN Operator = '=' THEN Age = 10
END

• 看到它在sqlfiddle中實時工作