There are many times where you'll want to see the relative contribution of a row (or group of rows) to the total row count. In other words, what percentage of the total count a row represents. To illustrate, let
17、避免不走索引的各种场景在下面的SQL语句中的WHERE子句不使用索引： 1）条件中有or，且or左右列并非全部由索引 Select col1 from table where key1=1 or no_key=22）like查询以%开头3）where条件仅包含复合索引非前置列Select col1 from table where key_part2=1 and key_part3=2索引包含key_part1，k...
SELECTobject_id, index_id, partition_number, row_group_id, delta_store_hobt_id, state, state_desc, total_rows, deleted_rows, size_in_bytesFROMsys.dm_db_column_store_row_group_physical_stats; 使用临时表提高性能 如果您加载数据的目的是为了在执行更多转换之前暂存它,那么将数据加载到堆表中要比加...
先建两个测试表table1和table2,两个表的数据很简单,其记录条数分别为2和4,具体如下: 假如现在要统计table1的id对应在table2中有多少条记录,保存在total字段里,这是经常会遇到的需求。如果按照常规的实现,就会先用select语句从table2中统计好数值,然后再写一个update语句更新到table1中,更新语句还得循环。这...
SELECT ProductID, QtyAvailable, UnitPrice, InventoryValue FROM dbo.Products; -- Update values in the table. UPDATE dbo.Products SET UnitPrice = 2.5 WHERE ProductID = 1; -- Display the rows in the table, and the new values for UnitPrice and InventoryValue. SELECT ProductID, QtyAvailabl...
IF DB_NAME() IN (SELECT databasename FROM #alldatabases) BEGIN INSERT #alltablesizes SELECT @@servername as servername, db_name() as databasename, s.name AS schemaname, t.name AS tablename, p.rows AS rowcounts, SUM(a.total_pages) * 8 AS totalspaceKB, SUM(a.used_pages) * 8 ...
table_name; 索引的统计信息 代码语言:javascript 代码运行次数:0 运行 AI代码解释 select INDEX_NAME, UNIQUENESS, BLEVEL BLev, LEAF_BLOCKS, DISTINCT_KEYS, NUM_ROWS, AVG_LEAF_BLOCKS_PER_KEY, AVG_DATA_BLOCKS_PER_KEY, CLUSTERING_FACTOR, GLOBAL_STATS, USER_STATS, SAMPLE_SIZE, to_char(t.last_...
7)rows MYSQL认为必须检查的用来返回请求数据的行数。 8)Extra 关于MYSQL如何解析查询的额外信息。效率最低的是Using temporary和Using filesort,意味着MYSQL根本不能使用索引,所以检索会很慢。 4、使用EXPLAIN中分析SQL性能 例1: 看左边sql语句的执行计划,看得出没有走任何索引,属于全表扫描,导致执行时间比较长。
SELECT TableName = obj.name, TotalRows = prt.rows, [SpaceUsed(KB)] = SUM(alloc.used_pages)*8 FROM sys.objects obj JOIN sys.indexes idx on obj.object_id = idx.object_id JOIN sys.partitions prt on obj.object_id = prt.object_id JOIN sys.allocation_units alloc on alloc.container_id ...
SELECTOBJECT_NAME(object_id)ASTableName,SUM(rows)ASTotalRowsFROMsys.partitionsWHEREindex_idIN(0,1)ANDOBJECT_NAME(object_id)NOTLIKE'sys%'GROUPBYOBJECT_NAME(object_id); 1. 2. 3. 4. 5. 在上面的示例中,我们使用了sys.partitions系统视图来获取数据库中所有表的数据条数。通过过滤index_id为 0 或...