mysql语句性能分析（一）

1.使用explain语句去查看分析结果

如explain select * from test1 where id=1;

会出现：id  selecttype  table  type possible_keys  key key_len  ref rows  extra各列。

其中，

type=const表示通过索引一次就找到了；

key=primary的话，表示使用了主键；

type=all,表示为全表扫描；

key=null表示没用到索引。type=ref,因为这时认为是多个匹配行，在联合查询中，一般为REF。

explain mysql语句；

eg:

EXPLAIN

SELECT 
	GoodsSku.sku_id, 
	GoodsSku.barcode, 
	GoodsSku.sku_name, 
	GoodsTypeSpec1.spec_name AS sku_spec1, 
	GoodsTypeSpec2.spec_name AS sku_spec2, 
	GoodsCategory1.cat_name AS catName1, 
	GoodsCategory2.cat_name AS catName2, 
	GoodsCategory3.cat_name AS catName3, 
	GoodsUnit.sale_unit, 
	SellerBase.seller_name, 
	IFNULL(
		(
			SELECT 
				SUM(WmsBatchItem.sku_num) 
			FROM 
				wms_batch_base AS WmsBatchBase 
				INNER JOIN wms_batch_item AS WmsBatchItem ON WmsBatchItem.batch_id = WmsBatchBase.batch_id 
			WHERE 
				WmsBatchItem.sku_id = GoodsSku.sku_id
		), 
		0
	) AS qichuNum, 
	IFNULL(
		(
			SELECT 
				SUM(
					WmsBatchItem.sku_num * WmsBatchItem.sku_price
				) 
			FROM 
				wms_batch_base AS WmsBatchBase 
				INNER JOIN wms_batch_item AS WmsBatchItem ON WmsBatchItem.batch_id = WmsBatchBase.batch_id 
			WHERE 
				WmsBatchItem.sku_id = GoodsSku.sku_id
		), 
		0
	) AS qichuPrice
FROM 
	goods_sku AS GoodsSku 
	INNER JOIN goods_base AS GoodsBase ON GoodsSku.goods_id = GoodsBase.goods_id 
	LEFT JOIN goods_category AS GoodsCategory1 ON GoodsCategory1.cat_id = GoodsBase.cat_id1 
	LEFT JOIN goods_category AS GoodsCategory2 ON GoodsCategory2.cat_id = GoodsBase.cat_id2 
	LEFT JOIN goods_category AS GoodsCategory3 ON GoodsCategory3.cat_id = GoodsBase.cat_id3 
	LEFT JOIN goods_unit AS GoodsUnit ON GoodsUnit.unit_id = GoodsBase.unit_id 
	LEFT JOIN seller_base AS SellerBase ON SellerBase.seller_id = GoodsBase.seller_id 
	LEFT JOIN goods_type_spec AS GoodsTypeSpec1 ON GoodsTypeSpec1.spec_id = GoodsSku.sku_spec1 
	LEFT JOIN goods_type_spec AS GoodsTypeSpec2 ON GoodsTypeSpec2.spec_id = GoodsSku.sku_spec2;

　　

 

然后可以根据这个来设置数据表的索引