MySQL ROW_COUNT() 在 Prepare 语句中不起作用

Question

我在做什么。

我有一个删除行的过程。

我将var_SelectedIds 作为, 分隔UUID()

然后

SET     @var_SQLStr = '';   
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'Delete ');
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'FROM DemoTable');        
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'WHERE DemoTableId IN (''',Replace(var_SelectedIds,',',''','''),'''); ');

-- SELECT @var_SQLStr;
PREPARE stmt FROM @var_SQLStr;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

我已经尝试过了。

// This is throwing SQL Syntax ERROR.

SET     @var_SQLStr = '';   
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'Delete ');
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'FROM DemoTable');        
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'WHERE DemoTableId IN (''',Replace(var_SelectedIds,',',''','''),'''); ');
SET     @var_SQLStr = CONCAT(@var_SQLStr ,' SELECT ROWS_COUNT() INTO @var_AffectedRows; ');

-- SELECT @var_SQLStr;
PREPARE stmt FROM @var_SQLStr;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

MySQL Reference

文本必须代表单个语句，而不是多个语句。

我也试过了

START TRANSACTION;

-- Other statements here

SET     @var_SQLStr = '';   
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'Delete ');
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'FROM DemoTable');        
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'WHERE DemoTableId IN (''',Replace(var_SelectedIds,',',''','''),'''); ');

-- SELECT @var_SQLStr;
PREPARE stmt FROM @var_SQLStr;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

SELECT ROW_COUNT() INTO @var_AffectedRows
COMMIT;

SELECT @var_AffectedRows AS NoOfRowsDeleted; // 0 output

我不知道行是如何被删除的。

Answer 1

你需要在EXECUTE之后和DEALLOCATE...之前执行SELECT ROW_COUNT()

START TRANSACTION;

-- Other statements here

SET     @var_SQLStr = '';   
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'Delete ');
SET     @var_SQLStr = CONCAT(@var_SQLStr ,'FROM DemoTable');        
SET     @var_SQLStr = CONCAT(@var_SQLStr ,' WHERE DemoTableId IN (''',Replace(var_SelectedIds,',',''','''),'''); ');
/*you need an additional whitespace here---^ */


-- SELECT @var_SQLStr;
PREPARE stmt FROM @var_SQLStr;
EXECUTE stmt;
SELECT ROW_COUNT() INTO @var_AffectedRows;
DEALLOCATE PREPARE stmt;

SELECT @var_AffectedRows; /*TADAAA!*/

COMMIT;