The number of records in the database table is:
Sql> Select COUNT (*) from table_name t;
1, using the statistical results of COUNT (*):
Sql> alter session Set Nls_language = "American";
Sql> set timing on;Sql>
How to display 0 in conditional [Group by] Report in count () SQL query
Challenge:Let me assume this: we have two tables, one is regions table with all region information (east, west, etc .) and we have another table with sales information. now, we
SQL tuning is primarily about reducing the number of consistent gets and physical reads.
COUNT (1) is compared with COUNT (*):
If your datasheet does not have a primary key, then count (1) is faster than COUNT (*)If you have a primary key, the
Case has two formats. Simple case function and case search function.--Simple case function when ' 1 ' then ' Male ' when ' 2 ' Then ' Women ' Else ' other ' end--case search function case when sex = ' 1 ' Then ' Man '
when sex = ' 2 '
Turn from: Nested transactions in SQL Server use--transaction count indicates a mismatch between the number of BEGIN and COMMIT statements--The underlying problemProblem:1. System.Data.SqlClient.SqlException (0x80131904): The transaction count after
In DB2, the sum function used to replace the count query is to calculate and sum the column values. The www.2cto.com count function accumulates the columns that meet the conditions and adds one when the conditions are met. The count function is
First, the questionToday there is a magical problem-there is data in the table, but the result of select COUNT (*) is 0.The initial manifestation of the problem is that the query report has no paging.At first, I thought it was a Java-side problem.
1.Select SUM (case if a.[status]=0 then 1 ELSE 0 End) as A1,SUM (case A.[status] When 1 then 1 ELSE 0 end) as A2,SUM (case A.[status] When 2 then 1 ELSE 0 end) as A3,A.userid,c.trainidFrom Coursewarelogmiddle A join Lessondetail BOn
MS SQL Server Query optimization methodThere are many reasons for the slow speed of queries, which are common1, no indexes, or no indexes (this is the most common problem with query slowness, is the flaw in programming)2, I/o throughput is small,
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