THIS TOPIC APPLIES TO: SQL Server (starting with 2008) Azure SQL Database Azure SQL Data Warehouse Parallel Data Warehouse. Updates query optimization statistics on. CREATE STATISTICS (Transact- SQL) | Microsoft Docs. THIS TOPIC APPLIES TO: SQL Server (starting with 2. Azure SQL Database. Azure SQL Data Warehouse Parallel Data Warehouse Creates query optimization statistics on one or more columns of a table, an indexed view, or an external table. For most queries, the query optimizer already generates the necessary statistics for a high- quality query plan; in a few cases, you need to create additional statistics with CREATE STATISTICS or modify the query design to improve query performance. To learn more, see Statistics. Transact- SQL Syntax Conventions. Syntax- - Syntax for SQL Server and Azure SQL Database. Create statistics on an external table. CREATE STATISTICS statistics_name. For Microsoft SQL Server, it's not recommended you use STATISTICS_NORECOMPUTE on indexes, but there are cases when you might be able to better control the updating of. If you're like me, you have a SQL Agent job in place to rebuild or reorganize only the indexes in your databases that truly require such actions. If you rely on the. Performance tuning is one of the major that database administrators need to perform when supporting very large databases. Analysis of present index usage is an. To keep SharePoint running with optimal performance, it's recommended to run the following maintenance tasks for your SharePoint databases: Check database. I am new to SQL Server statistics. Could you please describe what are the benefits of using the Auto Create Statistics and Auto Update Statistics options? I am also. ON { table_or_indexed_view_name } ( column [ .. WITH FULLSCAN ] . Create statistics on a regular table or indexed view. CREATE STATISTICS statistics_name. ON { table_or_indexed_view_name } ( column [ .. WHERE < filter_predicate> ]. FULLSCAN. [ [ , ] PERSIST_SAMPLE_PERCENT = { ON | OFF } ]. SAMPLE number { PERCENT | ROWS }. PERSIST_SAMPLE_PERCENT = { ON | OFF } ]. STATS_STREAM = stats_stream ] ]. NORECOMPUTE ]. [ [ , ] INCREMENTAL = { ON | OFF } ]. AND < conjunct> ]. IN (constant ,…). IS | IS NOT | = | < > | != | > | > = | !> | < | < = | !<. Syntax for Azure SQL Data Warehouse and Parallel Data Warehouse. CREATE STATISTICS statistics_name. ON [ database_name . WHERE < filter_predicate> ]. FULLSCAN. | SAMPLE number PERCENT. AND < conjunct> ]. There can be a situation where you have to use a cursor, even though the experts say not to use cursors or to avoid them as much as possible. But if you look closely. IN (constant ,…). IS | IS NOT | = | < > | != | > | > = | !> | < | < = | !<. Argumentsstatistics_name. Is the name of the statistics to create. Is the name of the table, indexed view, or external table on which to create the statistics. To create statistics on another database, specify a qualified table name. One or more columns to be included in the statistics. The columns should be in priority order from left to right. Only the first column is used for creating the histogram. All columns are used for cross- column correlation statistics called densities. You can specify any column that can be specified as an index key column with the following exceptions: Xml, full- text, and FILESTREAM columns cannot be specified. Computed columns can be specified only if the ARITHABORT and QUOTED_IDENTIFIER database settings are ON. CLR user- defined type columns can be specified if the type supports binary ordering. Computed columns defined as method invocations of a user- defined type column can be specified if the methods are marked deterministic. WHERE < filter_predicate>. Specifies an expression for selecting a subset of rows to include when creating the statistics object. Statistics that are created with a filter predicate are called filtered statistics. The filter predicate uses simple comparison logic and cannot reference a computed column, a UDT column, a spatial data type column, or a hierarchy. ID data type column. Comparisons using NULL literals are not allowed with the comparison operators. Use the IS NULL and IS NOT NULL operators instead. Here are some examples of filter predicates for the Production. Bill. Of. Materials table: WHERE Start. Date > '2. 00. AND End. Date < = '2. WHERE Component. ID IN (5. WHERE Start. Date IN ('2. AND End. Date IS NOT NULLFor more information about filter predicates, see Create Filtered Indexes. FULLSCANCompute statistics by scanning all rows. FULLSCAN and SAMPLE 1. PERCENT have the same results. FULLSCAN cannot be used with the SAMPLE option. When omitted, SQL Server uses sampling to create the statistics, and determines the sample size that is required to create a high quality query plan SAMPLE number { PERCENT | ROWS }Specifies the approximate percentage or number of rows in the table or indexed view for the query optimizer to use when it creates statistics. For PERCENT, number can be from 0 through 1. ROWS, number can be from 0 to the total number of rows. The actual percentage or number of rows the query optimizer samples might not match the percentage or number specified. For example, the query optimizer scans all rows on a data page. SAMPLE is useful for special cases in which the query plan, based on default sampling, is not optimal. In most situations, it is not necessary to specify SAMPLE because the query optimizer already uses sampling and determines the statistically significant sample size by default, as required to create high- quality query plans. SAMPLE cannot be used with the FULLSCAN option. When neither SAMPLE nor FULLSCAN is specified, the query optimizer uses sampled data and computes the sample size by default. We recommend against specifying 0 PERCENT or 0 ROWS. When 0 PERCENT or ROWS is specified, the statistics object is created but does not contain statistics data. PERSIST_SAMPLE_PERCENT = { ON | OFF }When ON, the statistics will retain the creation sampling percentage for subsequent updates that do not explicitly specify a sampling percentage. When OFF, statistics sampling percentage will get reset to default sampling in subsequent updates that do not explicitly specify a sampling percentage. The default is OFF. Applies to: SQL Server 2. SP1 CU4. STATS_STREAM =stats_stream Identified for informational purposes only. Not supported. Future compatibility is not guaranteed. NORECOMPUTEDisable the automatic statistics update option, AUTO_STATISTICS_UPDATE, for statistics_name. If this option is specified, the query optimizer will complete any in- progress statistics updates for statistics_name and disable future updates. To re- enable statistics updates, remove the statistics with DROP STATISTICS and then run CREATE STATISTICS without the NORECOMPUTE option. Warning Using this option can produce suboptimal query plans. We recommend using this option sparingly, and then only by a qualified system administrator. For more information about the AUTO_STATISTICS_UPDATE option, see ALTER DATABASE SET Options (Transact- SQL). For more information about disabling and re- enabling statistics updates, see Statistics. INCREMENTAL = { ON | OFF }When ON, the statistics created are per partition statistics. When OFF, stats are combined for all partitions. The default is OFF. If per partition statistics are not supported an error is generated. Incremental stats are not supported for following statistics types: Statistics created with indexes that are not partition- aligned with the base table. Statistics created on Always On readable secondary databases. Statistics created on read- only databases. Statistics created on filtered indexes. Statistics created on views. Statistics created on internal tables. Statistics created with spatial indexes or XML indexes. Applies to: SQL Server 2. SQL Server 2. 01. Permissions Requires one of these permissions: ALTER TABLE User is the table owner Membership in the db_ddladmin fixed database role SQL Server can use tempdb to sort the sampled rows before building statistics. Statistics for external tables When creating external table statistics, SQL Server imports the external table into a temporary SQL Server table, and then creates the statistics. For samples statistics, only the sampled rows are imported. If you have a large external table, it will be much faster to use the default sampling instead of the full scan option. Statistics with a filtered condition Filtered statistics can improve query performance for queries that select from well- defined subsets of data. Filtered statistics use a filter predicate in the WHERE clause to select the subset of data that is included in the statistics. When to Use CREATE STATISTICS For more information about when to use CREATE STATISTICS, see Statistics. Referencing Dependencies for Filtered Statistics The sys. Consider the operations that you perform on table columns before creating filtered statistics because you cannot drop, rename, or alter the definition of a table column that is defined in a filtered statistics predicate. Limitations and Restrictions. Updating statistics is not supported on external tables. To update statistics on an external table, drop and re- create the statistics. You can list up to 6. Examples. Examples use the Adventure. Works database. A. Using CREATE STATISTICS with SAMPLE number PERCENT The following example creates the Contact. Mail. 1 statistics, using a random sample of 5 percent of the Business. Entity. ID and Email. Promotion columns of the Contact table of the Adventure. Works. 20. 12database. CREATE STATISTICS Contact. Mail. 1. ON Person. Person (Business. Viewing the Last Updated Date for Statistics. Question: You talked about when statistics get updated last week. How can I see when the statistics were last updated? Answer: Actually, this question is much more interesting than it seems. Most people think the only way to access the "last modified date" for a statistic is to access it through the header information using DBCC SHOW_STATISTICS: DBCC SHOW_STASTISTICS ('tablename', 'index or statistics name'). It's true that the first result set shows the "header" information including when the statistics were last updated (second column in first result set) but how can you use this data programmatically? Related: Update the Statistics on Recently Modified Tables Only. In SQL Server 2. 00. STAT_HEADER (as well as DENSITY_VECTOR and HISTOGRAM) as options to DBCC SHOW_STATISTICS. Each of these, when added, will produce ONLY that particular tabular data set. As a result, you can INSERT/EXEC the output from the statistics header (or any of the others) into a table. Once the data's in a table then you can programmatically analyze it. For example, you could run automation routines that do things like: If the stats are more than a week old. ORIf the stats were last updated using a sampling (rows sampled < rows)then, update statistics with a fullscan. How can you programmatically analyze the statistics header? You need to pre- create the table and then use dynamic string execution. CREATE TABLE Statistics. Header. Name sysname. Updated datetime. Rows] bigint. Rows. Sampled bigint. Steps tinyint. Density decimal(9,5). Average. Key. Length decimal(9,5). String. Index nchar(3). Filter. Expression nvarchar(1. Unfiltered. Rows bigint. INSERT Statistics. Header. EXEC ('DBCC SHOW_STATISTICS (''tablename'', ''index/statistics name'') WITH stat_header')go. SELECT * FROM Statistics. Headergo. With the Statistics. Header table you can analyze all aspects of when the statistics were last created/updated as well as whether or not it was handled through a fullscan or a sampling. This really allows for a lot of automation options! But, if you just want the date (and date alone), I have a far easier way to get it. I just need the date! Isn’t there an easier way? There’s a simple (but not well- known) function called stats_date that’s been around since the 6x days. However, where you use it has changed over the years. When column- level statistics first came out (in SQL Server 7. IDs with indexes. In total, you could not have more than 2. AND column- level statistics. To find information about statistics, you’d use sysindexes. Related: Making the Most of Automatic Statistics Updating. In SQL Server 2. 00. IDs for column- level statistics from nonclustered index IDs and created a catalog view to see them: sys. However, sys. stats shows ALL statistics – even those on indexes. As a result, if you’re looking for last updated date for all of your statistics then just query sys. SELECT OBJECT_NAME(object_id) AS Object. Name,STATS_DATE(object_id, stats_id) AS Statistics. Date,*FROM sys. stats. Related: The Importance of SQL Server Statistics.
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