Question

考虑：

SET @PREFIX='DEV_';

SET @REFRESHDB=CONCAT(@PREFIX,'Refresh');

CREATE TABLE @REFRESHDB.`Metadata`
(
    `Key` VARCHAR(30) NOT NULL,
    `Value` VARCHAR(30) NOT NULL,
    PRIMARY KEY (`Key`)
) ENGINE = InnoDB;

INSERT INTO @REFRESDB.`Metadata` (`Key`, `Value`) VALUES ("Version", "0");

这似乎没有效果：mysql回来了：

您的SQL语法有错误;检查与MySQL服务器版本对应的手册，以便在“@REFRESHDB .Metadata”附近使用正确的语法

据我所知，根据the documentation，我已经完成了正确的事情。然而MySQL表示不允许这样做。这是MySQL的一些限制（不允许使用变量作为标识符）还是别的什么？

Answer 1

您必须使用prepare语句/动态sql来执行此操作。

本文详细介绍了这两个方面：

http://rpbouman.blogspot.com/2005/11/mysql-5-prepared-statement-syntax-and.html

试试这个：

SET @PREFIX='DEV_';

SET @REFRESHDB=CONCAT(@PREFIX,'Refresh');

SET @st = CONCAT('CREATE TABLE ', @REFRESHDB,'.`Metadata`
(
    `Key` VARCHAR(30) NOT NULL,
    `Value` VARCHAR(30) NOT NULL,
    PRIMARY KEY (`Key`)
) ENGINE = InnoDB');

PREPARE tStmt FROM @s;
EXECUTE tStmt;


SET @s = CONCAT('INSERT INTO ', @PREFIX, '.`Metadata` (`Key`, `Value`) VALUES ("Version", "0")');

PREPARE stmt FROM @s;
EXECUTE stmt;

Answer 2

文档说明：

“可以从一组有限的数据类型中为用户变量分配值：整数，十进制，浮点，二进制或非二进制字符串或NULL值”

您正在尝试将变量用作对象。这不受支持。

Answer 3

我建议你写一个存储过程：

DELIMITER $$
CREATE PROCEDURE (IN DBname varchar(255)
                , IN AKey varchar(255)
                , IN AValue varchar(255))
BEGIN
  DECLARE query VARCHAR(1000);
  -- First check the DBName against a list of allowed DBnames, 
  -- to prevent SQL-injection with dynamic tablenames.

  DECLARE NameAllowed BOOLEAN;
  SELECT 1 INTO NameAllowed WHERE DBName IN ('validDB1','validDB2');
  IF (NameAllowed = 1) THEN BEGIN

  -- DBName is in the whitelist, it's safe to continue.
    SET query = CONCAT('INSERT INTO '
                      ,DBName
                      ,'.MetaData (`key`,`value`) values (?,?));
    -- note the use of parameter placeholders, to prevent SQL-injection.
    PREPARE stmt FROM query;
    EXECUTE stmt USING Akey, AValue;
    DEALLOCATE PREPARE stmt; -- clears the query and its result from the cache.
  END; END IF;
END $$

DELIMITER ;

如何根据变量选择架构？

3 个答案: