MariaDB 10.0 和 MariaDB 10.1 存储过程中 PREPARE FROM EXECUTE 区别

前景：

　　有一个更新表分区的存储过程，在MariaDB10.1.12下，是能正常运行的。某些业务要求，我同步了这个存储过程到另一台服务器的数据库中，版本为MariaDB10.0.19，这个存储过程执行报错！

　　存储过程如下：

 CREATE  PROCEDURE `proc_accesslog_partition_add`(in dbname VARCHAR(20), in tablename VARCHAR(30), in accdate VARCHAR(20))

BEGIN -- dbname 数据库名；tablename：表名；accdate：日期 DECLARE conditionSql VARCHAR(2000);  DECLARE alterStr VARCHAR(1000);  SET conditionSql = CONCAT("SELECT * FROM information_schema.partitions where table_schema='",dbname,"' and table_name='",tablename,"' AND PARTITION_NAME='p",accdate,"'");  SET alterStr = CONCAT("ALTER TABLE ",tablename," ADD PARTITION (PARTITION p",accdate," VALUES LESS THAN (TO_DAYS('",accdate,"')))");

 SET @STR=CONCAT("IF NOT EXISTS(",conditionSql,") THEN ",alterStr,";END IF;");  PREPARE mainStmt FROM @STR;  EXECUTE mainStmt;

END

　　在10.1下，这个过程是能正常执行的。

　　但是在10.0下，它会抱如下错误：

[SQL]CALL proc_test('ad_warehouse','t_access_log_30','20160323'); [Err] 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'IF NOT EXISTS(SELECT * FROM information_schema.partitions where table_schema='a' at line 1

MySQL prepare语法： PREPARE statement_name FROM preparable_SQL_statement; /*定义*/ EXECUTE statement_name [USING @var_name [, @var_name] ...]; /*执行预处理语句*/ {DEALLOCATE | DROP} PREPARE statement_name /*删除定义*/ ;

　　重新修改存储过程：

BEGIN -- dbname 数据库名；tablename：表名；accdate：日期 DECLARE num INT;  SET @if_sql = CONCAT("SELECT count(*) INTO @record FROM information_schema.partitions where table_schema='",dbname,"' and table_name='",tablename,"' AND PARTITION_NAME='p",accdate,"'");  SET @alter_sql = CONCAT("ALTER TABLE ",tablename," ADD PARTITION (PARTITION p",accdate," VALUES LESS THAN (TO_DAYS('",accdate,"')))");  PREPARE ifStmt FROM @if_sql;  EXECUTE ifStmt;  deallocate prepare ifStmt;

 SET num=@record;  IF num=0 THEN  PREPARE alterStmt FROM @alter_sql;  EXECUTE alterStmt;  deallocate prepare alterStmt;  END IF;

END

　　这个过程能在10.0和10.1下执行成功。

　　这个结果说明

　　　　1、mariaDB10.0 的prepare from execute语法中，preparable_SQL_statement只支持简单的SQL语句，不支持if exists 等复杂语句。

　　　　2、动态SQL语法执行，需要PREPARE FROM EXECUTE 来实现。

　　　　3、在存储过程需要获取上一个结果作为条件，用INTO，但有一点需要记住，EXECUTE只把@开头的当做参数。