sql - 截断表和更新统计信息

Question

调用 Truncate table 后是否需要更新表统计信息，或者它会自动更新？

问:截断表后是否需要调用“UPDATE STATISTICS”？

Answer 1

在再次需要统计数据之前，统计数据不会自动更新。也就是说，TRUNCATE 不会执行此操作。 所以“不”。

最初的答案是"is"，因为它不是自 Action 为 TRUNCATE 的一部分。这取决于您如何阅读问题:-)

请记住，统计信息会在查询需要时自动更新(例如行更改数)。来自 BOL 中的“Index Statistics”

A statistics update is initiated whenever the statistics used in a query execution plan fail a test for current statistics

使用 STATS_DATE 进行验证的一种方法...

SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id)
FROM
   sys.indexes 
WHERE
   object_id = OBJECT_ID('MyTruncatedTable')

编辑:我想确定一下:-)

您将看到统计信息仅由 SELECT 语句更新，而不是由 INSERT、DELETE 或 TRUNCATE 更新

IF OBJECT_ID('dbo.foo') IS NOT NULL DROP TABLE dbo.foo
CREATE TABLE dbo.foo (
    bar int NOT NULL IDENTITY (1, 1) PRIMARY KEY,
    thing int NOT NULL
)
CREATE INDEX IX_thing ON dbo.foo (thing)

INSERT dbo.foo (thing) SELECT c1.object_id FROM sys.columns c1, sys.columns c2
SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id) AS AfterLoad
FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo')

SELECT DISTINCT thing FROM dbo.foo ORDER BY thing DESC
SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id) AS AfterFirstQuery
FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo')

DELETE TOP (50000) dbo.foo
SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id) AS AfterDelete
FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo')

SELECT DISTINCT thing FROM dbo.foo ORDER BY thing DESC
SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id) AS After2ndQuery
FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo')

TRUNCATE TABLE dbo.foo
SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id) AS AfterTruncate
FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo')

SELECT DISTINCT thing FROM dbo.foo ORDER BY thing DESC
SELECT
   name AS index_name, 
   STATS_DATE(object_id, index_id) AS After3rdQuery
FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo')