SqlServer 索引

BranchInfo 表索引设置

--表扫描,索引无效
SELECT * FROM dbo.BranchInfo WHERE LEN(PoiId)>0

--索引扫描
SELECT * FROM dbo.BranchInfo WHERE PoiId<>''

--索引扫描
SELECT * FROM dbo.BranchInfo WHERE PoiId IS NOT NULL AND PoiId<>''

--表扫描,索引无效
SELECT * FROM dbo.BranchInfo WHERE PoiId IS NULL OR PoiId=''

--索引扫描
SELECT * FROM dbo.BranchInfo WHERE ISNULL(PoiId,'')<>''

--表扫描,索引无效
SELECT * FROM dbo.BranchInfo WHERE PoiId IS NULL
UNION
--索引扫描
SELECT * FROM dbo.BranchInfo WHERE PoiId =''

SqlServer执行计划