indexing

问题 Say I have a table in a SQL 2005 database with 2,000,000+ records and a few indexes. What advantage is there to using index hints in my queries? Are there ever disadvantages to using index hints in queries? 回答1: First, try using SQL Profiler to generate a .trc file of activity in your database for a normal workload over a few hours. And then use the "Database Engine Tuning Advisor" on the SQL Server Management Studio Tools menu to see if it suggests any additional indexes, composite indexes,

问题 Say I have a table in a SQL 2005 database with 2,000,000+ records and a few indexes. What advantage is there to using index hints in my queries? Are there ever disadvantages to using index hints in queries? 回答1: First, try using SQL Profiler to generate a .trc file of activity in your database for a normal workload over a few hours. And then use the "Database Engine Tuning Advisor" on the SQL Server Management Studio Tools menu to see if it suggests any additional indexes, composite indexes,

问题 How can I index the last axis of a Numpy array if I don't know its rank in advance? Here is what I want to do: Let a be a Numpy array of unknown rank. I want the slice of the last k elements of the last axis. If a is 1D, I want b = a[-k:] If a is 2D, I want b = a[:, -k:] If a is 3D, I want b = a[:, :, -k:] and so on. I want this to work regardless of the rank of a (as long as the rank is at least 1). The fact that I want the last k elements in the example is irrelevant of course, the point is

问题 How can I index the last axis of a Numpy array if I don't know its rank in advance? Here is what I want to do: Let a be a Numpy array of unknown rank. I want the slice of the last k elements of the last axis. If a is 1D, I want b = a[-k:] If a is 2D, I want b = a[:, -k:] If a is 3D, I want b = a[:, :, -k:] and so on. I want this to work regardless of the rank of a (as long as the rank is at least 1). The fact that I want the last k elements in the example is irrelevant of course, the point is

问题 For an app like iOS Messages: How should I design the server database queries & schema? Queries Create a user. Get a user's chats. Get the messages between two users. Add a message to a chat (creating the chat if it doesn't yet exist). Note : Every chat only has two users (no group chats). Every chat's id equals this unique unordered pairing function applied to user_id & with_id . How should I query a user's chats, each with its latest message? Example User Interface (UI) See my design &

问题 I need to update existing MS SQL indexed view by including additional columns values from newly created table. Indexed view: CREATE OR ALTER VIEW [dbo].[MySelectionInfo] WITH schemabinding AS SELECT C.Id id0, C.Code Code1, C.Name Name2, C.ProgramLevel Level3, C.Department Department4, C.City City10, C.STATE State11, C.StartDate StartDate12, C.Deadline Deadline13, B.ID Table_B_ID, A.Id Table_A_ID FROM dbo.Table_A A INNER JOIN dbo.Table_B B ON A.id = B.Table_A_Id INNER JOIN dbo.Table_C C ON C

问题 I have a sort of FIZZ-BUZZ problem. I have a calendar with weekdays. In the next column I put 'FIZZ' at certain rows. If there is an empty gap between two 'FIZZ' I put 'BUZZ' in between except if the weekday is 'SUN'. See the code below (I use 0.15.2 pandas version): import datetime import pandas as pd dict_weekday = {1: 'MON', 2: 'TUE', 3: 'WED', 4: 'THU', 5: 'FRI', 6: 'SAT', 7: 'SUN'} df = pd.DataFrame(pd.date_range(datetime.date(2014, 1, 1), datetime.date(2014, 1, 10), freq='D'), columns=[

问题 Are indices (indexes) defined as UNIQUE case sensitive in MySQL? 回答1: It depends on the collation of the field - if it's ci (case insensitive) or cs (case sensitive). The unique index would apply accordingly. 回答2: You can make a column case-sensitive by using this syntaxis. the unique index also will be case-sensitive. ALTER TABLE tbl_name MODIFY col_name column_definition [CHARACTER SET charset_name] [COLLATE collation_name] Example: ALTER TABLE `tablename` MODIFY `column` VARCHAR(100)

问题 Are indices (indexes) defined as UNIQUE case sensitive in MySQL? 回答1: It depends on the collation of the field - if it's ci (case insensitive) or cs (case sensitive). The unique index would apply accordingly. 回答2: You can make a column case-sensitive by using this syntaxis. the unique index also will be case-sensitive. ALTER TABLE tbl_name MODIFY col_name column_definition [CHARACTER SET charset_name] [COLLATE collation_name] Example: ALTER TABLE `tablename` MODIFY `column` VARCHAR(100)

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . I used to program in Java and Python earlier, but recently have started using MATLAB for lots of stuff (specifically computer vision algorithms). However MATLAB has indexing of arrays beginning from 1 instead of 0, which is the norm in almost every programming languages I