Question

如何使用变量表示MySQL中的字符串值？下面的存储过程包含两个变量@varname和@file1。它还使用concat()从@file1创建一个字符串，但这些字符串值都没有正确填充到脚本中。（查询未加载结果，并且未创建outfile。）如何修复此代码以使其有效？

DELIMITER $$

DROP PROCEDURE IF EXISTS `parse_descriptions`$$
CREATE PROCEDURE `parse_descriptions`()
BEGIN

SET @varname='something';
SET @file1= concat('D:/mypath/','@varname');

select d.id, d.term, d.conceptid from dtablename as d 
where term like '%@varname%' 
into outfile concat('@file1','_test.txt') 
fields terminated by '\t'
optionally enclosed by ""
lines terminated by '\r\n'
;

END$$

CALL `parse_descriptions`()$$

DROP PROCEDURE IF EXISTS `parse_descriptions`$$

Answer 1

修改了你的代码。认为你在几个地方引用了错误

SET @varname='something';
SET @file1= concat('D:/mypath/',@varname);   --here

select d.id, d.term, d.conceptid from dtablename as d 
where term like concat('%', @varname, '%') -- here
into outfile concat(@file1,'_test.txt')  -- here
fields terminated by '\t'
optionally enclosed by ""
lines terminated by '\r\n'
;

Answer 2

除了在参数周围的几个地方错放引号之外，因为我已经评论过最大的问题是你试图在select ...into outfile命令中使用变量，这只能通过prepared statement完成。下面包含的样本[已测试且工作正常]。您可以根据需要进行相应的更改。

DELIMITER $$
CREATE PROCEDURE `parse_descriptions`()
BEGIN
SET @varname='harikas';
SET @file1= concat('D:/SO_Test/',@varname, '_test.txt');

SET @sql = CONCAT('select * from teachers where username like ''%', @varname, '%'' into outfile ''', @file1 , '''');
select @sql;
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END$$

准备好的语句将生成如下所示的查询

select * from teachers where username like '%harikas%' into outfile 
'D:/SO_Test/harikas_test.txt'

调用程序

call parse_descriptions()

编辑：您在该行末尾缺少'。您修改过的程序应该是

DELIMITER $$
DROP PROCEDURE IF EXISTS `parse_descriptions`$$
CREATE PROCEDURE `parse_descriptions`()
BEGIN

SET @varname='something';
SET @file1= concat('D:/mypath/',@varname, '_test.txt');

SET @sql = concat('select d.id, d.term, d.cid from dtablename as d where term like ''%', @varname, '%'' into outfile ''', @file1 , ''' fields terminated by ''\t'' optionally enclosed by "" lines terminated by ''\r\n''');
select @sql;
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END$$

在存储过程中使用变量作为字符串

2 个答案: