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