mysql - 程序mysql中cursol中的错误查询

Question

我对 curosr 有疑问，完全是查询：SELECT Crc32 FROM tableName。我想从 Crc32 列中读取所有行，并根据前四个字符找到一个与四个数字同名的表

错误：

0   12:58:57    call ShowNewUserComments("User66")  Error Code: 1146. Table 'comments.tableName' doesn't exist

调用程序：

call ShowNewUserComments("User66");

代码

DELIMITER $$
DROP PROCEDURE IF EXiSTS ShowNewUserComments $$
CREATE PROCEDURE `ShowNewUserComments`(tableName varchar(255)/*, Date TIMESTAMP*/)
BEGIN


             DECLARE recordNotFound INTEGER DEFAULT 0;
             DECLARE oneRow VARCHAR(10) DEFAULT "";
             DECLARE getCrc32,i int (11);
             DECLARE myCursor CURSOR FOR SELECT Crc32 FROM tableName;    
             DECLARE CONTINUE HANDLER FOR NOT FOUND SET recordNotFound = 1; 
             OPEN myCursor;
            set i = 0;
             allRows: LOOP
                FETCH myCursor INTO oneRow;
                   set  i = i + 1;
                     IF recordNotFound THEN
                        LEAVE allRows;
                     END IF;

             END LOOP allRows;
             CLOSE myCursor;

END

Answer 1

您不能直接将变量中的表名替换为 MySQL 中的查询，因为您需要像这样使用动态 sql PREPARE：

DELIMITER $$
DROP PROCEDURE IF EXiSTS ShowNewUserComments $$
CREATE PROCEDURE `ShowNewUserComments`(tableName varchar(255)/*, Date TIMESTAMP*/)
BEGIN

     DECLARE recordNotFound INTEGER DEFAULT 0;
     DECLARE oneRow VARCHAR(10) DEFAULT "";
     DECLARE getCrc32,i int (11);
     DECLARE myCursor CURSOR FOR SELECT Crc32 FROM temp_table;
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET recordNotFound = 1;


    DROP TEMPORARY TABLE IF EXISTS temp_table;

    SET @query1 = CONCAT('CREATE TEMPORARY  TABLE temp_table AS
                            SELECT Crc32
                            FROM ',tableName,' ');
    PREPARE stmt FROM @query1; EXECUTE stmt; DEALLOCATE PREPARE stmt;


     OPEN myCursor;
     set i = 0;
     allRows: LOOP
        FETCH myCursor INTO oneRow;
           set  i = i + 1;
             IF recordNotFound THEN
                LEAVE allRows;
             END IF;

     END LOOP allRows;
     CLOSE myCursor;

    DROP TEMPORARY TABLE IF EXISTS temp_table;
END