Question

set @tabela='cliente';

set @campo='codigo';

set @t1 = concat('SELECT count(0) FROM information_schema.COLUMNS WHERE 
information_schema.COLUMNS.TABLE_NAME =',@tabela,' AND 
information_schema.COLUMNS.COLUMN_NAME =',@campo);

PREPARE teste FROM @t1;

execute teste;

=============================================== ================

[SQL] set @tabela='cliente'; Affected rows: 0 Time: 0.003ms

[SQL] set @campo='codigo'; Affected rows: 0 Time: 0.001ms

[SQL] 
set @t1 = concat('SELECT count(0) FROM information_schema.COLUMNS WHERE information_schema.COLUMNS.TABLE_NAME =',@tabela,' AND information_schema.COLUMNS.COLUMN_NAME =',@campo);
Affected rows: 0
Time: 0.001ms

[SQL] PREPARE teste FROM @ t1; [错误] 1054 - 未知专栏＆＃39; cliente＆＃39;在＆＃39; where子句＆＃39;

* 为什么？ *

Answer 1

您的选择如下：

SELECT count(0) FROM information_schema.COLUMNS
WHERE information_schema.COLUMNS.TABLE_NAME = cliente

它应该是这样的：

SELECT count(0) FROM information_schema.COLUMNS
WHERE information_schema.COLUMNS.TABLE_NAME = 'cliente'

添加必要的引号。我不知道确切的语法。可能是

TABLE_NAME =''',@tabela,'''

或

TABLE_NAME =\'',@tabela,'\'

编辑：我查了一下。根据{{3}}，两个版本都是正确的。

Answer 2

我认为你错过了该表名的'。

您目前正在执行的是

... WHERE information_schema.COLUMNS.TABLE_NAME = cliente AND information_schema.COLUMNS.COLUMN_NAME = codigo;

这是不正确的。

如果您已使用预准备语句，则应通过参数绑定提供这些数据。

像

这样的东西

set @t1 = SELECT count(0) FROM information_schema.COLUMNS WHERE 
    information_schema.COLUMNS.TABLE_NAME = ? AND 
    information_schema.COLUMNS.COLUMN_NAME = ?';
PREPARE teste FROM @t1;
EXECUTE teste USING @tablea, @campo;

应该有用。

Answer 3

问题是没有引用表名：

set @t1 = concat('SELECT count(0) FROM information_schema.COLUMNS WHERE 
information_schema.COLUMNS.TABLE_NAME =''',@tabela,''' AND 
information_schema.COLUMNS.COLUMN_NAME =''',@campo, '''');

Answer 4

因为你知道名字......

set @t1 = concat('SELECT count(0) FROM information_schema.COLUMNS WHERE 
information_schema.COLUMNS.TABLE_NAME ='cliente' AND 
information_schema.COLUMNS.COLUMN_NAME ='codigo');

你错过了报价。

Answer 5

请使用'''那里的varchar或文本值，看起来像你的查询：

    declare @tabela varchar(200);
    declare @campo varchar(200);
    declare @t1 varchar(200);


    set @tabela='cliente';
    set @campo='codigo';
    set @t1 = concat('SELECT count(0) FROM information_schema.COLUMNS WHERE 
    information_schema.COLUMNS.TABLE_NAME =''',@tabela,''' AND 
    information_schema.COLUMNS.COLUMN_NAME =''',@campo,'''');


    PREPARE teste FROM @t1;

    execute teste;

Answer 6

您没有用引号括起数据：

sqlfiddle！ http://sqlfiddle.com/#!2/0b900/15

（这次是正确的链接）

set @t1 = concat('SELECT count(0) FROM information_schema.COLUMNS WHERE 
information_schema.COLUMNS.TABLE_NAME ="',@tabela,'" AND 
information_schema.COLUMNS.COLUMN_NAME ="',@campo,'"');

1054 - 'where子句'中的未知列'cliente'

6 个答案: