Mysql 在不带子查询的where子句中使用用户变量
我有以下情况:Mysql 在不带子查询的where子句中使用用户变量,mysql,Mysql,我有以下情况: +-----------+ | my_column | +-----------+ | A | | B | | C | | D | | E | +-----------+ 对于这个例子,我简化了下面的函数 DROP FUNCTION IF EXISTS my_function; CREATE FUNCTION my_function( phrase VARCHAR(255), co
+-----------+
| my_column |
+-----------+
| A |
| B |
| C |
| D |
| E |
+-----------+
对于这个例子,我简化了下面的函数
DROP FUNCTION IF EXISTS my_function;
CREATE FUNCTION my_function(
phrase VARCHAR(255),
column_value VARCHAR(255)
)
RETURNS FLOAT(20,10)
READS SQL DATA
SQL SECURITY INVOKER
BEGIN
IF(column_value = 'A') THEN RETURN 1.0000000000;
ELSEIF(column_value = 'B') THEN RETURN 0.7500000000;
ELSEIF(column_value = 'C') THEN RETURN 0.7500000000;
ELSEIF(column_value = 'D') THEN RETURN 0.5000000000;
ELSEIF(column_value = 'E') THEN RETURN 0.0000000000;
END IF;
END;
以下是我的主要存储过程:
DROP PROCEDURE IF EXISTS my_procedure;
CREATE PROCEDURE my_procedure(
IN phrase VARCHAR(255)
)
READS SQL DATA
SQL SECURITY INVOKER
BEGIN
SET @phrase = phrase;
SET @query = "
SELECT
my_column,
@score_var := my_function(?,my_column) as score,
@score_var
FROM my_table
ORDER BY score DESC;
";
PREPARE stmt FROM @query;
EXECUTE stmt USING @phrase;
DEALLOCATE PREPARE stmt;
END;
现在如果我调用我的程序
称我的程序为“任何东西”
结果是:
+-----------+--------------+------------+
| my_column | score | @score_var |
+-----------+--------------+------------+
| A | 1.0000000000 | 1 |
| B | 0.7500000000 | 0.75 |
| C | 0.7500000000 | 0.75 |
| D | 0.5000000000 | 0.5 |
| E | 0.0000000000 | 0 |
+-----------+--------------+------------+
+-----------+--------------+------------+
| my_column | score | @score_var |
+-----------+--------------+------------+
| A | 1.0000000000 | 1 |
| C | 0.7500000000 | 0.75 |
| E | 0.0000000000 | 0 |
+-----------+--------------+------------+
但如果我在我的\u过程的查询中添加WHERE@score\u var>0.5,结果是:
+-----------+--------------+------------+
| my_column | score | @score_var |
+-----------+--------------+------------+
| A | 1.0000000000 | 1 |
| B | 0.7500000000 | 0.75 |
| C | 0.7500000000 | 0.75 |
| D | 0.5000000000 | 0.5 |
| E | 0.0000000000 | 0 |
+-----------+--------------+------------+
+-----------+--------------+------------+
| my_column | score | @score_var |
+-----------+--------------+------------+
| A | 1.0000000000 | 1 |
| C | 0.7500000000 | 0.75 |
| E | 0.0000000000 | 0 |
+-----------+--------------+------------+
预期结果´>0.5´:
+-----------+--------------+------------+
| my_column | score | @score_var |
+-----------+--------------+------------+
| A | 1.0000000000 | 1 |
| B | 0.7500000000 | 0.75 |
| C | 0.7500000000 | 0.75 |
+-----------+--------------+------------+
我见过一些使用子查询的答案,但我的问题是:在这种情况下,我可以不使用子查询吗
也欢迎使用其他方法。当您在同一语句中读写用户变量时,该行为将被记录为未记录。换句话说,除非您阅读并理解MySQL版本的源代码,否则结果是不可预测的 然而,我认为你不必要地把事情复杂化了。我不认为有理由使用预先准备好的语句,也不认为有理由使用u用户变量。您的程序主体可以是:
SELECT
my_column,
my_function(phrase, my_column) as score,
FROM my_table
HAVING score > 0.5
ORDER BY score DESC
此外,您的函数可以用较少的代码重复编写:
RETURN
CASE column_value
WHEN 'A' THEN 1.0000000000
WHEN 'B' THEN 0.7500000000
WHEN 'C' THEN 0.7500000000
WHEN 'D' THEN 0.5000000000
WHEN 'E' THEN 0.0000000000
END
是的,先生。。。以我的尊敬回应。还感谢您提供了代码更少的示例