随机获取表若干行

过程执行后会随机从表中筛选指定数目的记录返回。过程包含三个参数，分别是表名，行数和主键id。过程只支持int类型单主键的表。主键可以省略为空，这样过程会自动查找主键，不过这样比较慢。 MySQL CREATE DEFINER=`root`@`%` PROCEDURE `rand_data`(IN `tbN

CREATE DEFINER=`root`@`%` PROCEDURE `rand_data`(IN `tbName` VARCHAR(50), IN `rowCnt` INT, IN `tbKey` VARCHAR(50))
	LANGUAGE SQL
	NOT DETERMINISTIC
	CONTAINS SQL
	SQL SECURITY DEFINER
	COMMENT '随机获取若干记录,只适用于单主键表'
BEGIN

	#获取主键名
	IF tbKey IS NOT NULL THEN
		SET @tbKey=tbKey;#参数里面已经有，这种情况比较快
	ELSE
		#参数里面没，从系统表查找主键，比较耗时
		SELECT @tbKey:=c.COLUMN_NAME
		FROM
	  		INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS t,
	  		INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS c
		WHERE
	  		t.TABLE_NAME = c.TABLE_NAME
	  		AND t.TABLE_SCHEMA = c.TABLE_SCHEMA
			AND t.TABLE_SCHEMA = database()
			AND t.TABLE_NAME = tbName
			AND t.CONSTRAINT_TYPE = 'PRIMARY KEY';
	END IF;
		
	#获取最大id,最小id和记录数
	SET @getMaxIdSql = CONCAT('SELECT @maxId:=MAX(', @tbKey, '),',
		'@minId:=MIN(', @tbKey, '),',
		'@totalCnt:=COUNT(', @tbKey, ')',
		' FROM `', tbName, '`;');
	PREPARE getMaxId FROM @getMaxIdSql;
	EXECUTE getMaxId;
	DEALLOCATE PREPARE getMaxId;
	
	#创建临时表
	DROP TABLE IF EXISTS rand_tt;
	SET @temTbSql = CONCAT('CREATE TEMPORARY TABLE rand_tt SELECT 0 aid,tb.* FROM `',tbName,'` tb LIMIT 0;');
	PREPARE temTb FROM @temTbSql;
	EXECUTE temTb;
	DEALLOCATE PREPARE temTb;
	
	#构建获取一条记录的sql
	SET @randRowSql = CONCAT('INSERT INTO rand_tt SELECT @cnt:=@cnt+1 aid,tb.* FROM ',
		tbName, ' tb WHERE tb.', @tbKey, '=?;');
	PREPARE addRow FROM @randRowSql;
	
	#生成随机记录
	SET @cnt=0;
	insertLoop: LOOP
		SET @id=FLOOR(RAND()*(@maxId-@minId)+@minId);
		IF NOT EXISTS (SELECT id FROM rand_tt WHERE id=@id) THEN
			EXECUTE addRow USING @id;
			IF @cnt >= rowCnt OR @cnt >= @totalCnt THEN
				LEAVE insertLoop;
			END IF;
		END IF;
	END LOOP insertLoop;	
	DEALLOCATE PREPARE addRow;
	
	#返回数据
	ALTER TABLE rand_tt DROP COLUMN aid;
	SELECT * FROM rand_tt;
END