一种方法可以完成这件事。最初的答案是sql server语法。此编辑具有mysql语法。确保不能同时访问临时表。e、 在mysql中，temp表对于连接是唯一的。同时添加错误检查。在mysql中，根据需要设置适当的varchar大小。我使用了1024全面只是为了测试的目的。

mysql语法

CREATE table test (
    id int,
    table_name varchar(1024),
    where_c varchar(1024)
);

INSERT into test(id, table_name, where_c) values
(1,'x','y=2'),
(2,'x','r=3'),
(3,'t','y=2');

DROP PROCEDURE IF EXISTS generate_sql;

DELIMITER //
CREATE PROCEDURE generate_sql()
BEGIN
DECLARE v_table_name VARCHAR(1024);
DECLARE v_where_c VARCHAR(1024);
DECLARE table_id INT;
DECLARE counter INT;
DECLARE v_SQL varchar(1024);

CREATE TEMPORARY table test_copy
SELECT * FROM test;

SET v_SQL = '';

SET counter = (SELECT COUNT(1) FROM test_copy);
WHILE counter > 0 DO
    SELECT id, table_name, where_c
    INTO table_id, v_table_name, v_where_c
    FROM test_copy LIMIT 1;

    SET v_SQL = CONCAT(v_SQL, 'SELECT * FROM ', v_table_name, ' WHERE ', v_where_c);

    DELETE FROM test_copy WHERE id=table_id;
    SET counter = (SELECT COUNT(1) FROM test_copy);

    IF counter > 0 THEN
        SET v_SQL = CONCAT(v_SQL,' UNION ');
    ELSE
        SET v_SQL = v_SQL;
    END IF;
END WHILE;

DROP table test_copy;

SELECT v_SQL;
END //
DELIMITER ;

call generate_sql()

sql server语法

CREATE table test (
    id int,
    table_name varchar(MAX),
    condition varchar(MAX)
);

INSERT into test(id, table_name, condition) values
(1,'x','y=2'),
(2,'x','r=3'),
(3,'t','y=2');

SELECT * INTO #temp FROM test;

DECLARE @SQL varchar(MAX);
SET @SQL='';

while exists (select * from #temp)
begin

    DECLARE @table_name varchar(MAX);
    DECLARE @condition varchar(MAX);
    DECLARE @table_id int;

    SELECT top 1 @table_id=id, @table_name=table_name, @condition=condition FROM #temp;

    SET @SQL += 'SELECT * FROM ' + @table_name + ' WHERE ' + @condition;

    delete #temp where id = @table_id;

    if exists (select * from #temp) SET @SQL += ' UNION ';
end

SELECT @SQL;
drop table #temp;

假设table x 以及 t 如果具有相同的定义，并且希望通过使用union而不是union all来忽略重复的结果，则应执行以下操作：

SET @sql = '';

SELECT GROUP_CONCAT(
  CONCAT('SELECT * FROM `', `table_name`, '` WHERE ', `condition`) 
  SEPARATOR ' UNION ') INTO @sql
FROM w;

SET @sql = CONCAT('SELECT * FROM ( ', @sql, ' ) a;');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

（我对你的问题稍加修改，因为你对表有两种不同的定义 x )