What's the syntax for getting the total number of rows in a particular table in a MySQL database?
I've always done
SELECT count(*) FROM table
The above will you give you the total count of all rows.
You could just as easily tack on a WHERE clause to get the count of some subset
SELECT count(*) FROM table WHERE foo = 'bar'
SELECT count(*)
FROM table_name
Related
I have a nested query. Any suggestion on how i can rewrite the nested query so that I am able to create a view with it
Here is the query
select *
from (select * from tracking_table order by id desc) x
group by labref);
There doesn't seem to be any need for the nested query. It can just be:
SELECT *
FROM tracking_table
GROUP BY labref
ORDER BY id DESC
But both queries probably don't do what you want. All the columns will be chosen from unpredictable rows in each group, and there's no guarantee that different columns will come from the same row. You're also not guaranteed to get the highest ID in each group.
If you want the row with the highest ID for each labref, see SQL select only rows with max value on a column
I'm trying to get distinct values from a table. When I ran select distinct count(id) from table I got over a million counts. However if I ran select count(distinct id) from table I've got only around 300k counts. What was the difference of the two queries?
Thanks
When you do select distinct count(id) then you are basically doing:
select distinct cnt
from (select count(id) as cnt from t) t;
Because the inner query only returns one row, the distinct is not doing anything. The query counts the number of rows in the table (well, more accurately, the number of rows where id is not null).
On the other hand, when you do:
select count(distinct id)
from t;
Then the query counts the number of different values that id takes on in the table. This would appear to be what you want.
If id is the pk the count with distinct count(id) will match the no of rows returned with count(distinct id).
If id is not the pk but has a unique constraint(on id alone, not in combination with any other column), the no of rows returned with count(distinct id) will be equal to the count with distinct count(id), as in the case of pk.
If id is just another column, select count distinct count(id) from table will return one row with the no of records where the id column is NOT NULL where as select count count(distinct id) from table will return 'one column' with all non NULL unique ids in the table.
In no case will the count or the no of rows returned exceed the total no of rows in your table.
The second select is definitely what you want, because it will aggregate the id's (if you have 10 records with id=5 then they will all be counted as one record) and the select will return "how many distinct id's were in the table".
However the first select will do something odd, and i'm not entirely sure what it will do.
Exist a better way to do what the following SQL query does? I have the feeling that table1 will be searched twice and may be that can be avoided with some trick and increase the efficient of the query, but I just can't figure out how ;( Here is the query (in MySQL):
SELECT a, SUM(count)
FROM table1
GROUP BY a
HAVING SUM(count) = (SELECT SUM(count) as total FROM table1 GROUP BY a ORDER BY total DESC LIMIT 1)
The goal is return the number(s) with the major accumulate, with its accumulate.
being table1 a two field table like:
a,count
1,10
1,30
1,0
2,1
2,100
2,4
3,10
4,50
4,55
The result with that data sample is:
2,105
4,105
Thanks in advance.
SELECT a, total FROM
(SELECT a AS a, SUM(COUNT) AS total
FROM table1
GROUP BY a) AS xyz
HAVING total = MAX(total)
Hope this will work for you
This sub-query is executed only once, and you don't have to bother with creating any pre-query as other answers may suggest (although doing so this is still correct, just not needed). Database engine will realise, that the sub-query is not using any variable dependent on the other part of the query. You can use EXPLAIN to see how the query is executed.
More on the topic in this answer:
https://stackoverflow.com/a/658954/1821029
I think you could probably do it by moving your HAVING sub-select query into its on prequery. Since it will always include a single row, you won't require any "JOIN", and it does not have to keep recomputing the COUNT(*) every time the HAVING is applied. Do it once, then the rest
SELECT
a,
SUM(count)
FROM
table1,
( SELECT SUM(count) as total
FROM table1
GROUP BY a
ORDER BY total DESC
LIMIT 1 ) PreQuery
GROUP BY
a
HAVING
SUM(count) = PreQuery.Total
This query return one row with two columns:
1- a list of comma separated values of "a" column, which have the biggest "Total"
2- and the biggest Total value
select group_concat(a), Total
from
(select a, sum(count) as Total
from table1
group by a) OnTableQuery
group by Total
order by Total desc
limit 1
Note that it queries table1 just one time. The query was already tested.
I wish to find the total number of distinct records in a table.
I have a table with the following columns
id, name, product, rating, manufacturer price
This has around 128 rows with some duplicates based on different column names.
I only want to select distinct rows:
select distinct name, product, rating, maufacturer, price from table
This returns 47 rows
For pagination purposes, I need to find the total number of distinct records, so I have another satatement:
select distinct count(name), product, rating, maufacturer, price from table
But this returns 128 instead of 47.
How can I get the total number of distinct rows? Any help will be much appreciated. Thanks
You have the distinct and count reversed.
SELECT COUNT(DISTINCT column_name) FROM table_name
Also, I would drop the extra fields when counting, your results will be unexpected for those other fields.
It is not quite clear if you want to get the count in the SAME query with the results or if you want to run a different query. Here go both solutions. In the result as a new column:
select distinct name, product, rating, manufacturer, price, (
select count(*) from (
select distinct name, product, rating, manufacturer, price from table1
) as resultCount) as resultCount
from table1
Notice the previous solution will repeat the count(*) for each row, which is not very efficient, not even visually appealing. Try running two queries one getting the actual data and the other one to get the amount of records in the table that match that data:
select distinct name, product, rating, manufacturer, price from table1
select count(*) from (
select distinct name, product, rating, manufacturer, price from table1
) as result
Hope this helps
Try adding GROUP BY name, product, rating, maufacturer, price clause
It would require running your actual query TWICE... an INNER for distinct and then get the count of those as a single row returned, and then join that to the original select distinct...
select distinct
t1.product,
t1.rating,
t1.maufacturer,
t1.price,
JustTheCount.DistCnt
from
table t1,
( select count(*) as DistCnt
from ( select distinct
t2.product,
t2.rating,
t2.maufacturer,
t2.price
from
table t2 )
) JustTheCount
In the following query, you're getting rows with distinct names since the DISTINCT clause precedes the name column:
SELECT DISTINCT name, product, rating, maufacturer, price FROM table
However, to get the count of the same records, use the following format:
SELECT COUNT(DISTINCT name) FROM table
Notice that DISTINCT goes inside of the COUNT function so that you're counting the distinct names. You probably don't want to include the other columns in the count query because they will be a random sample from the set. Of course, if you want a random sample, then include them.
Most applications will run the count query first, followed by the query to return the results. Also keep in mind that COUNT(*) is only an estimate, and the value may differ from the actual number of records returned.
SELECT DISTINCT COUNT(name), product FROM table isn't even a valid query in MySQL 4.x. You can't mix aggregate and non-aggregate columns. IN 5.x, it'll run, but the values for the non aggregate columns will be a random sample from the set.
At the risk of sparking some flames here.. you could always use:
SQL_CALC_FOUND_ROWS as the first part of your SQL. This is very mysql specific though.
http://dev.mysql.com/doc/refman/5.0/en/information-functions.html
mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name
-> WHERE id > 100 LIMIT 10;
mysql> SELECT FOUND_ROWS();
I am trying to select of the duplicate rows in mysql table it's working fine for me but the problem is that it is not letting me select all the fields in that query , just letting me select the field name i used as distinct , lemme write the query for better understading
mysql_query("SELECT DISTINCT ticket_id FROM temp_tickets ORDER BY ticket_id")
mysql_query("SELECT * , DISTINCT ticket_id FROM temp_tickets ORDER BY ticket_id")
1st one is working fine
now when i am trying to select all fields i am ending up with errors
i am trying to select the latest of the duplicates let say ticket_id 127 is 3 times on row id 7,8,9 so i want to select it once with the latest entry that would be 9 in this case and this applies on all the rest of the ticket_id's
Any idea
thanks
DISTINCT is not a function that applies only to some columns. It's a query modifier that applies to all columns in the select-list.
That is, DISTINCT reduces rows only if all columns are identical to the columns of another row.
DISTINCT must follow immediately after SELECT (along with other query modifiers, like SQL_CALC_FOUND_ROWS). Then following the query modifiers, you can list columns.
RIGHT: SELECT DISTINCT foo, ticket_id FROM table...
Output a row for each distinct pairing of values across ticket_id and foo.
WRONG: SELECT foo, DISTINCT ticket_id FROM table...
If there are three distinct values of ticket_id, would this return only three rows? What if there are six distinct values of foo? Which three values of the six possible values of foo should be output?
It's ambiguous as written.
Are you looking for "SELECT * FROM temp_tickets GROUP BY ticket_id ORDER BY ticket_id ?
UPDATE
SELECT t.*
FROM
(SELECT ticket_id, MAX(id) as id FROM temp_tickets GROUP BY ticket_id) a
INNER JOIN temp_tickets t ON (t.id = a.id)
You can use group by instead of distinct. Because when you use distinct, you'll get struggle to select all values from table. Unlike when you use group by, you can get distinct values and also all fields in table.
You can use DISTINCT like that
mysql_query("SELECT DISTINCT(ticket_id), column1, column2, column3
FROM temp_tickets
ORDER BY ticket_id");
use a subselect:
http://forums.asp.net/t/1470093.aspx