What is the difference between the following two sql
statements
select count(*) from <tablename>
select count(col_name) from <tablename>
Answers were Sorted based on User's Feedback
Answer / debasis
select count(*) from <tablename> returns the number of rows
in the table.
select count(col_name) from <tablename> return number
values in the column (Ignores null value in the colum). For
example if we execute the following 2 queries then
select count(*) form emp
select count(comm) form emp
The result will be
14
4
| Is This Answer Correct ? | 34 Yes | 7 No |
Answer / kushi
for the First Qry,result is "No.of records"
for the second Qry,result is "No.of records for particular
columnname"
| Is This Answer Correct ? | 17 Yes | 0 No |
Answer / sandeep
select count(*) from <tablename>
- return number of records from table
select count(col_name) from <tablename>
- return number of records where col_name is NOT NULL
- Null value is eliminated by an aggregate or other SET
operation.
| Is This Answer Correct ? | 5 Yes | 0 No |
Answer / sql2000
There seem to be a problem with the solutions provided by
the above.
Both the counts should provide the same result which is the
no of rows in the table.
count (*) will result in a bigger table scan than count
(col_name) hence its advisable to use count(1) while
calculating the count for a table.
Correct me if I am wrong...:)
| Is This Answer Correct ? | 1 Yes | 3 No |
What is primary key and example?
Create Index myIndex On myTable(myColumn) What type of Index will get created after executing the above statement
What should be the fill factor for indexes created on tables? : sql server database administration
Which is the main third-party tool used in sql server?
What is data integrity? Explain constraints?
How can we solve concurrency problems?
What are window functions in sql server?
What is sql service broker?
What is difference between primary key and foreign key?
Do you know what is user defined datatypes and when you should go for them?
Explain query editor regions
Where are sql server usernames and passwords stored in the sql server?
Oracle (3253)
SQL Server (4518)
MS Access (429)
MySQL (1402)
Postgre (483)
Sybase (267)
DB Architecture (141)
DB Administration (291)
DB Development (113)
SQL PLSQL (3330)
MongoDB (502)
IBM Informix (50)
Neo4j (82)
InfluxDB (0)
Apache CouchDB (44)
Firebird (5)
Database Management (1411)
Databases AllOther (288)