20120810 tsql tips
- 1. by Anney 09/04/12 1
- 2. • COUNT(*) •8 • COUNT(Name) •6 • COUNT(DISTINCT Name) •4 09/04/12 2
- 3. • COUNT(*) • returns the number of items in a group. This includes NULL values and duplicates. • COUNT(ALL expression) • evaluates expression for each row in a group and returns the number of nonnull values. • COUNT(DISTINCT expression) • evaluates expression for each row in a group and returns the number of unique, nonnull values. • Tips • If return values greater than 2^31-1, COUNT produces an error. • COUNT_BIG() 09/04/12 3
- 4. • REPLICATE • REPLICATE('0', 4 - LEN(3)) + CONVERT(varchar(4), 3) • POWER • RIGHT(CONVERT(varchar(10), POWER(10, 4) + 3), 4) • 10000 + 3 => ‘10003’ • Tips: • POWER ( float_expression , y ) • 數值轉型兩次 (int -> float, float -> varchar) • RIGHT • RIGHT('0000' + CONVERT(varchar(4), 3), 4) • ‘0000’ + ‘3’ => ‘00003’ 09/04/12 4
- 5. • sp_who2 procedure • 所有連線狀況 , 也可以看到連線是否有被卡住 (Blocked) 的狀況。 09/04/12 5
- 6. • sys.dm_exec_requests • sys.dm_exec_sql_text(sql_handle | plan_handle) 09/04/12 6
- 7. • http:// msdn.microsoft.com/en-us/library/ms175997(SQL.105). aspx • http://msdn.microsoft.com/en-us/library/ms174276.aspx • http://blog.miniasp.com/post/2010/05/19/T-SQL-Tips-Fixed-Le • http://blog.miniasp.com/post/2010/10/13/How-to-get- current-executing-statements-in-SQL-Server.aspx • http://msdn.microsoft.com/en-us/library/ms177648.aspx • http://msdn.microsoft.com/en-us/library/ms181929.aspx 09/04/12 7
- 8. 09/04/12 8